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1
Lewallen, Melissa A. « The Metabolic Physiology of Planarian Flatworms ». Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538679/.
Texte intégralRésumé :
Using a high throughput closed respirometry method to measure oxygen consumption, I determined metabolic rates in asexual and sexual Schmidtea mediterranea and Girardia dorotocephala, as a function of temperature, taxon, stressors, reproductive mode, age, regeneration, and specific dynamic action. This study has shown that oxygen consumption can reliably be measured in planaria using optode closed respirometry, and also provided a reliable method for measuring wet mass in planaria, which has been a challenge to researchers in the past. This research revealed that oxygen consumption in S. mediterranea is 1.5-2.1X greater in the sexual strain over the asexual strain at 13-18°C. Within the sexual strain, oxygen consumption is 1.5 -2.2X greater in sexually mature adults over the sexually immature groups (hatchlings, juveniles, and regenerating sexuals). Furthermore, I was able to quantify differences in sexual morphology between these groups exhibiting significant differences in oxygen consumption. The results of this research supports a theory of higher metabolic costs with sexual maturity in S. mediterranea. Therefore, this study has established sexual and asexual S. mediterranea as simple, yet attractive models for investigating energetic costs between sexual and asexual phenotypes. This research also provided quantitative values for specific dynamic action in planaria, with a maximum increase in oxygen consumption of 160% induced by feeding, as well as metabolic relationships in planaria involving temperature, age, and regeneration. These values establish planaria as one of the simplest animal models in which common metabolic patterns, such as SDA and poikilothermic temperature sensitivity, have been demonstrated. Therefore, this research has contributed to the overall knowledge of the basic physiology in this animal, providing the framework for future metabolic studies in planaria involving environmental factors, reproduction, regeneration, development, and aging. Information from this study may supplement interpretation and understanding of modern cellular, molecular, and genomic studies in planaria.
2
Mustonen, Katie Lynn. « Endocannabinoid System in a Planarian Model ». Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc33188/.
Texte intégralRésumé :
In this study, the presence and possible function of endocannabinoid ligands in the planarian is investigated. The endocannabinoids ananadamide (AEA) and 2-arachidonoylglycerol (2-AG) and entourage NAE compounds palmitoylethanolamide (PEA), stearoylethanolamide (SEA) and oleoylethanolamide (OEA) were found in Dugesia dorotocephala. Changes in SEA, PEA, and AEA levels were observed over the initial twelve hours of active regeneration. Exogenously applied AEA, 2-AG and their catabolic inhibition effected biphasic changes in locomotor velocity, analogous to those observed in murines. The genome of a close relative, Schmidtea mediterranea, courtesy of the University of Utah S. med genome database, was explored for cannabinoid receptors, none were found. A putative fatty acid amide hydrolase (FAAH) homolog was found in Schmidtea mediterranea.
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An, Yang. « Genome analysis of the planarian Dugesia japonica ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199140.
Texte intégral
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Tan, Thomas Ching-Jen. « Telomere biology in the freshwater planarian Schmidtea mediterranea ». Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12308/.
Texte intégralRésumé :
Freshwater planarian Schmidtea mediterranea is an emerging model for studying in vivo gene functions and regulation in native cell niches. The obligate asexual strain of this species reproduces by fission, in which succession of soma occurs without passing through the germline. To achieve this somatic immortality the somatic stem cells need to overcome the end replication problem. Therefore it can be hypothesised that somatic telomere maintenance in asexual S. mediterranea must possess a germ-like property, with which age-related erosions can be adequately repaired. In this PhD project, the telomere repeat unit in S. mediterranea was confirmed to be the vertebrate-like TTAGGG. Attrition of whole body telomere length was found in ageing sexual worms and also in asexual worms which had not gone through recent fission events. Opposite telomere length dynamics were observed in regenerated samples of the two strains, with erosion in the sexuals and reset in the asexuals. The telomere maintenance was found to increase during regeneration in both strains, with a higher level of increase in asexual worms. A homolog of the telomerase reverse transcriptase subunit, Smed_Tert, was identified and characterised in this organism. High level of Smed_Tert expression was seen in germ cells in mature sexual worms and adult stem cells in asexual worms. Knockdown of Smed_Tert expression by RNA interference caused progressive telomere erosion, however effects on cell proliferation and viability have not been observed in knockdown samples. Four alternate splice isoforms of Smed_Tert were identified. The enhanced telomerase activity during regeneration correlates with a proportional increase in the full-length isoform and a decrease in isoforms with a truncated TRBD domain, suggesting a dominant negative regulation of telomerase by alternative splicing. Significant increase in the expression of the full-length isoform was seen in regenerating asexual samples but not in sexual strains, which correlates with their telomere length dynamics. It is hoped that the comparative studies between the sexual and asexual strains can improve our understanding of how soma can evolve to become an effective inheritable unit.
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Shen, Yun, et 沈筠. « The role of extracellular matrix in planarian regeneration ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206722.
Texte intégral
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Lapan, Sylvain William. « Regeneration and maintenance of the planarian nervous system ». Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/87912.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references
Planarians can regenerate all tissues, including the central nervous system and the eyes. This process depends on a population of cells in the adult, the neoblasts, that includes pluripotent stem cells. Whether the neoblast population also includes progenitors specialized for forming specific lineages has not been demonstrated. This thesis describes the identification of progenitors that contribute to eyes during regeneration. Expression and functional analyses identified the genes eyes absent, six- 1/2 and ovo as critical for the formation of all cells of the eye. otxA and soxB were specifically required for photoreceptor regeneration, and sp6-9 and dlx were required for regeneration of the optic pigment cup. Expression analysis of these transcription factors in situ revealed that eye progenitors were distributed in mesenchymal trails extending posteriorly from the regenerating eye. These progenitors originate in the neoblasts, and promixity to the eye primordium correlates with increased differentiation. The spatial and genetic identification of a progenitor population in planarians elucidates migratory and morphogenetic mechanisms underlying organ regeneration in these animals. RNA sequencing of eye tissue also identified hundreds of genes with highly enriched expression in the eye, including numerous orthologs of eye pathology-related gene as well as likely components of key visual processes such as phototransduction and optic pigment cell function. The planarian brain is composed of dozens of cell types with regionalized distribution. The function of the planarian hedgehog gene in the patterning of CNS regions was investigated. hedgehog was expressed in the medial planarian brain, flanked by nkx2 and nkx6, then pax6b, and finally dlx-1 and msx at the most distal positions. This organization is similar to the expression domains of orthologous transcription factors in the vertebrate neural tube. However, in contrast to vertebrates, the expression of nkx2, nkx6, and pax6b in planarians was not affected by loss of hedgehog expression. RNA sequencing analysis identified a strong effect of Hedgehog signaling genes on a medially positioned cell with glia-like features. Therefore, Hedgehog signaling affects formation of at least one cell type in the planarian brain, but does not broadly regulate transcription factor expression domains and cell type identity.
by Sylvain William Lapan.
Ph. D.
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Kravarik, Kellie M. (Kellie Marie). « Neoblast specialization during regeneration of the planarian S. mediterranea ». Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115681.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2018.Cataloged from PDF version of thesis. "Due to the condition of the original material, there are unavoidable flaws in this reproduction. Table 3.1 is missing from page 167"-- Disclaimer Notice page.
Includes bibliographical references (pages 175-186).
Planarians are well known for their ability to regenerate an entire animal from small tissue fragments. Planarian regeneration requires a population of dividing cells called neoblasts that are distributed throughout the body. Historically, neoblasts have been considered a homogeneous population of stem cells capable of differentiating into all cell types. Most studies, however, analyze neoblasts at the population rather than the single cell level, making it difficult to determine how heterogeneous the neoblast population is. A bulk RNA sequencing approach with expression screening identified 33 new transcription factors transcribed in specific differentiated cells that were also expressed in small fractions of neoblasts during regeneration. Transcription factors of distinct differentiated tissues were expressed in different subsets of neoblasts, whereas transcription factors expressed in the same differentiated tissues were expressed in the same neoblasts. These results suggest roles for neoblast-expressed transcription factors in the specification of distinct tissues. Furthermore, the transcription factors klf, Pax3/7, and FoxA were required for the differentiation of cintillo-expressing sensory neurons, dopamine- beta-hydroxylase-expressing neurons, and the pharynx, respectively. The planarian nervous system is comprised of numerous different cell types, providing an opportunity to study how neoblasts acquire the diverse cell fates that comprise a particular tissue. We used single-cell sequencing to identify the transcriptomes of hundreds of planarian neurons and neoblasts. Using computational analysis of these data we identified the transcriptomes of several specific types of planarian neuronal cells, including cholinergic, dopaminergic, and serotonergic neurons, as well as glial cell types. In neoblasts, we identified a population of cells that expressed both markers of differentiated neurons and transcription factors expressed in various neural cell types, which we hypothesize to be neural specialized neoblasts. We found a number of unique populations of neural neoblasts that correspond with specific neural sub-types. Interestingly, however, these neural specialized neoblasts do not express a detectable unified gene regulatory network. These results are consistent with direct specification of neural sub-types in neoblasts and suggest that neoblasts do not differentiate down a highly hierarchical lineage path as has been described for many developmental lineages.
by Kellie M. Kravarik.
Ph. D.
8
Cote, Lauren E. (Lauren Esther). « The instructive roles of muscle cells in planarian regeneration ». Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122066.
Texte intégralRésumé :
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2019
Cataloged from student-submitted PDF version of thesis. Vita.
Includes bibliographical references.
Regeneration requires both new cell production and patterning information to correctly place new tissue. Planarians are flatworms with remarkable capacity to regenerate after nearly any injury and to indefinitely maintain tissue homeostasis. Dividing cells, neoblasts, are the source of all new tissue, whereas positional information is hypothesized to be harbored by post-mitotic muscle, including the subepidermal body wall musculature. Single-muscle-cell mRNA sequencing along the anterior-posterior axis revealed regional gene expression within muscle cells. The resulting axial gene expression map included FGF receptor-like (FGFRL) homologs and genes encoding components of Wnt signaling. Two distinct FGFRL-Wnt circuits, involving juxtaposed anterior FGFRL and posterior Wnt expression domains, controlled head and trunk patterning.
Inhibition of FGFRL-Wnt circuit components led to the formation of ectopic posterior eyes or secondary pharynges, indicating their importance in maintaining the anterior-posterior axis. Inhibition of different myogenic transcription factors specifically ablated orthogonal subsets of the body wall musculature. Longitudinal fibers, oriented along the anterior-posterior axis, are required for regeneration initiation. Circular fibers maintained medial-lateral patterning during head regeneration. During early regeneration, transcriptional changes in muscle cells comprised part of a generic wound response displayed by all injuries, from incisions to decapitations. The sole exception to this generic response was the expression in body-wall muscle of the Wnt inhibitor notum, which occurs preferentially at anterior-facing wounds in longitudinal muscle fibers. Therefore, anterior-posterior polarity, the choice of head or tail regeneration, involves longitudinal body wall muscle fibers.
Planarian muscle were found to be highly secretory. Combining an in silico definition of the planarian matrisome and recent whole animal single-cell transcriptome data revealed that muscle is a major source of extracellular matrix (ECM). Inhibition of hemicentin-1 (hmcn-1), which encodes a highly conserved ECM glycoprotein expressed in body wall muscle, resulted in ectopic localization of internal cells, including neoblasts, outside of the muscle fiber layer. ECM secretion and maintenance of tissue separation indicated that muscle functions as planarian connective tissue. Whereas muscle is often viewed as a strictly contractile tissue, these findings reveal that planarian muscle has specific regulatory roles in axial patterning, wound signaling, and tissue architecture to enable correct regeneration.
by Lauren E. Cote.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Biology
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Abnave, Prasad. « Exploring mammalian immunity against intracellular bacteria through planarian flatworms ». Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM5049.
Texte intégralRésumé :
Les interactions hôte-pathogène sont un jeu vaste et complexe entre agent pathogène et hôtepour la victoire de la bataille de la pathogenèse. Plusieurs organismes modèles sont étudiéspour illustrer les mécanismes impliqués dans ces interactions. Dans ma thèse, j'ai utilisé lesplanaires comme un organisme modèle pour explorer les interactions hôte-pathogène. Comme les différents organismes modèles peuvent mettre enévidence les différentes caractéristiques de l'immunité, j'ai décidé de tirer avantage del'absence de connaissances sur l'immunité des planaires en explorant l'inexplorée. Dans monprojet, j'ai infecté les planaires avec 16 bactéries pathogènes : les planaires y sont très résistantes. Pour en explorer lemécanisme j'ai effectué un profilage du transcriptome à partir deplanaires infectées, suivie par un criblage par ARN interférence des gènes up-régulés. J'aidécouvert les gènes qui régissent la résistance antibactérienne dans les planaires, et de façonintéressante, le criblage a permis de mettre en évidence un gène, MORN2, dont la fonctionimmunologique était complètement inconnue. L'induction et l'extinction de l'expression de MORN2dans les macrophages ont révélé que MORN2 contrôle l'internalisation, la réplication et letrafic des bactéries à l'intérieur de la cellule. Dans mon étude, j'ai démontré que MORN2 estun composant de la phagocytose associée à LC3 et qu'il peut surmonter le blocage de lafusion phagolysosomale imposée par les bactéries pathogènes. Ainsi ma thèse met en avantl'importance d'utiliser des organismes modèles inhabituels afin de dévoiler des mécanismesinexplorées et des molécules impliquées dans les interactions hôte-pathogèneHost-pathogen interaction is a vast and complex interplay between pathogen and hostto conquer the battle of pathogenesis. Several model organisms are being studied to illustratethe mechanisms involved in these interactions. In my thesis I have used planarians as a modelorganism to explore host-pathogen interactions. As different model organismscan highlight different features of immunity I decided to take advantage of lack of knowledgeabout planarian immunity and get benefits from exploring unexplored. In my project I haveinfected planarians with 16 pathogenic bacteria and I found that in contrary to othercommonly used model organisms such as Drosophila, C. elegans and zebrafish the planariansare highly resistant to bacterial infections. To explore the mechanism behind this resistance Iperformed infection induced transcriptome profiling followed by RNA interference screeningof up-regulated gens. I discovered genes governing antibacterial resistance in planarians andinterestingly the screening highlighted a gene MORN2 of which the immunological functionwas completely unknown. The human ortholog of MORN2 is then further assessed for itsantimicrobial function. Induced expression and down regulation of MORN2 in macrophagesrevealed that MORN2 controls uptake, replication and trafficking of bacteria inside the cell.In my study I demonstrated that MORN2 is a component of LC3-associated phagocytosis andit can overcome phagosome maturation blockage imposed by pathogenic bacteria. Thus mythesis propounds the importance of using unusual model organisms to unveil unexploredmechanisms and molecules involved in host-pathogen interactions
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Baptista, Vanessa dos Anjos. « Estrutura e composição de comunidades de tricladidos terrestres (Platyhelminthes : Tricladida : Terricola) em áreas de floresta estacional decidual do sul do Brasil ». Universidade do Vale do Rio do Sinos, 2007. http://www.repositorio.jesuita.org.br/handle/UNISINOS/2302.
Texte intégralRésumé :
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Previous issue date: 30Bolsa para curso e programa de Pós Graduação
As planárias terrestres formam um grupo relativamente numeroso em espécies (cerca de 800 espécies) com distribuição mundial, principalmente pan-tropical. Muitas espécies de planárias terrestres são especialistas de hábitat e, em geral, apresentam capacidade de locomoção reduzida, havendo assim, muitas espécies endêmicas. Sua utilização em estudos de diversidade, visando determinar áreas prioritárias para conservação, é indicada por serem predadores de topo de cadeia alimentar no seu microhábitat. No Brasil, um grande número de espécies de planárias terrestres foi registrado em áreas originalmente cobertas por floresta ombrófila densa localizadas nos estados de Santa Catarina, São Paulo e Rio de Janeiro. Estudos recentes da composição e da estrutura de comunidades de Terricola, realizados no Rio Grande do Sul, têm se concentrado na região do Planalto das Araucárias, no nordeste do estado, em áreas de floresta ombrófila, registrando um elevado número de espécies de planárias terrestres em diferentes localidades
Land flatworms constitute a relatively species rich zoological group, being distributed world wide, but mainly pan-tropical. They show very strict habitat requirements and a reduced locomotion capacity, so that there are many endemic species. Their use as indicator-taxa in conservation and biodiversity studies is recomended because land planarians are top-predatores within their soil ecosystem. In Brazil, the diversity of land planarians is better known in areas that were originally covered by the southeastern dense ombrophilous forest, located in the states of São Paulo, Rio de Janeiro e Santa Catarina. Recent studies on the composition and structure of land planarian communities, mainly done in the region of the Planalto das Araucárias, located at the northeast of Rio Grande do Sul state, in areas of mixed and dense ombrophilous forest, have registered high species richness in various localities, many of the species being new taxa and/or endemic for each type of forest. The caducifolious forest is one of th
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Felix, Daniel André. « PBC and MEIS class genes in the planarian Schmidtea mediterranea ». Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.575479.
Texte intégralRésumé :
Planarians have outstanding regenerative capabilities which depend on the presence of a pool of somatic stem cells. In addition planarians keep perfect proportion of the body while degrowing during starvation. While the establishment and maintenance of the anteroposterior (AlP) axis has been shown to depend on Wnt and Hedgehog signalling, not much is known about the subsequent patterning events. PBC and MEIS class genes are evolutionary conserved TALE homeobox genes with important functions in patteming and cell differentiation. They are well known co-factors of the Hox genes however they also have other Hox-independent functions. The aim of this study was to identify the planarian orthologs of the PBC and MEIS class genes and to examine their putative role in anteroposterior patteming. Here one PBC class gene, Smed-pbx, and the three MEIS class genes Smed-meis I , Smed-meis2 and Smed-prep were identified and orthology established through phylogenetic analyses. Smed-prep was found to define the cephalic area in which the anterior structures are formed, most prominently the brain. In anterior regenerating Smed-prep(RNAi) worms a reduction or even complete absence of the brain and anterior markers was observed. Importantly, the differentiation of stem cells into nerve cells was shown not to be dependent on Smed-prep. In step with its function the Smed-prep gene was found to have an anteroposterior bias in expression, being highly expressed in the head. While both Smed-meis genes were found to be important for regeneration and maintenance of the eyes and for the adaptation of the body to the new size of the animal after amputation, Smed-pbx was found to have pleiotropic functions, phenocopying aspects of all three MEIS class genes upon RNAi interference, and also producing additional phenotypes. This study has found that the four planarian orthologs of PBC and MEIS class genes are important players in regeneration. Two genes, Smed-pbx and especially Smed-prep, have been found to be necessary for anteroposterior patterning. This is the first time that a homeobox transcription factor has been directly implicated in anteroposterior patterning in planarians.
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Sheng, Wanhui. « AN EXTENSION OF PLANARIAN BEHAVIORAL MODEL : CANNABINOID PHYSICAL DEPENDENCE AND WITHDRAWAL ». Master's thesis, Temple University Libraries, 2016. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/402376.
Texte intégralRésumé :
Pharmaceutical SciencesM.S.
Background: Planarians have mammalian-like neurotransmitter systems and have been established as a novel in vivo model for neuropharmacology. In previous research, planarians exposed to the cannabinoid receptor (CB-R) agonist WIN 55,212-2 (10 μmol/L) for 1 h displayed a significant (p < 0.05) decrease in spontaneous locomotor velocity (pLMV) when subsequently tested in drug-free, but not in drug-containing, water. This demonstrated abstinence-induced withdrawal from a CB-R agonist as a manifestation of the development of physical dependence. Purpose: The purpose of the present study was to extend previous work and to further establish a cannabinoid behavioral model with planarians. Specifically, the goals included (i) confirm the work with WIN 55,212-2 and extend to a second agonist (ii) interfere with agonist-induced physical dependence using several CB-R antagonists, (ii) demonstrate antagonist-induced precipitated withdrawal behavior, and (iii) try to induce withdrawal behavior from CB-R agonists using UV light. Methods: Two CB agonists (WIN 55,212-2 and JWH251) and four CB antagonists (AM251, AM281, SLV319 and SR144528) were used. Planarians were placed individually in CB-R agonist or agonist + antagonist mixtures for 20 and 30 min of exposure (with or without UV radiation), and withdrawal was quantified by measuring pLMV in drug-free vs drug-containing water (with or without UV light irradiation). Results: (i) Four different CB1-R antagonists (AM251, AM281, SLV319 and SR144528) dose-relatedly blocked development of physical dependence induced by two different CB-R agonists (WIN 55,212-2 and JWH251). (ii) None of the same four antagonists (AM251, AM281, SLV319 and SR144528) precipitated withdrawal. (iii) Short wavelength (254 nm), but not long wavelength (366 nm), UV light attenuated abstinence-induced withdrawal from WIN 55,212-2, while short wavelength UV light induced moderate withdrawal behavior. Conclusions: The results confirm the use of a planarian model as a simple yet robust way to study development of physical dependence to cannabinoid agonists. The model is more rapid and sensitive than the usual rodent models. The effect of UV irradiation adds to the supposition that the results are receptor-related. The results also give rise to the surprising suggestion, within the limitations of the methodology, that development of cannabinoid physical dependence and antagonist-induced precipitated withdrawal might be separable phenomena in planarians.
Temple University--Theses
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Fincher, Christopher T. (Christopher Terry). « Comprehensive single-cell transcriptional profiling of the regenerative planarian Schmidtea mediterranea ». Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129053.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references.
Animals can contain hundreds of cell types, each of which has a distinct morphology and function. The transcriptome of a cell dictates this unique cell biology. Recent approaches for high throughput single-cell RNA sequencing have made it possible to generate transcriptomes easily and affordably for tens of thousands of single cells, raising the possibility that transcriptomes could be generated for all cell types and cell states in a complete animal. Planarians are freshwater flatworms renowned for their capacity for whole-body regeneration. They possess a complex body plan with multiple distinct tissues. They also possess a population of dividing cells, called neoblasts, which contain pluripotent stem cells and are the source of all new tissue, with all cell types being turned over throughout the life of the animal. Planarians also constitutively express an arrangement of regionally expressed genes in their muscle that serve as patterning information for the animal.
As such, at a single time point in the adult, pluripotent stem cells, all differentiated cells, and all associated transition states from stem cell to differentiated cell can be recovered, including patterning information expressed in muscle. This makes planarians ideally suited to generating an atlas of transcriptomes for all cell types and cell states in a whole animal. We used the single- cell RNA sequencing technology Drop-seq to determine the transcriptomes for 66,783 cells from adult planarians. In doing so, we identified a number of known and novel cell populations, including a novel class of phagocytic cells. We also uncovered novel neoblast subpopulations and putative transition state populations between neoblasts and differentiated cells, as well as a number of genes with regional expression in muscle.
Through the identification of known rare cell types in the data, we conclude that we have obtained near-to-complete cell type saturation for all cell types and cell states in the adult planarian. We now have full transcriptomes for each of these cell populations, which can be utilized to assay their roles in planarian biology. This approach can also be applied widely to diverse animal species, including those with limited molecular tools available.
by Christopher T. Fincher.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Biology
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Rojo, Laguna José Ignacio. « Proliferative and positional instructions underliying planarian regeneration and tissue renewal = Instrucciones proliferativas y posicionales subyacentes a la regeneración y el recambio tisular en planaria ». Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/406952.
Texte intégralRésumé :
Some animals have incredible regenerative abilities which kept researchers fascinating during decades. How these animals are able to regenerate missing parts and restore damaged tissues can give researchers insights in the regenerative medicine field. Here, we use the planarian Schmidtea mediterranea, specie which is able to fully regenerate every missing part, to deeper understand the regeneration and the tissue renewal processes. Both processes share several mechanisms which are essentials for their correct development. In this Thesis, we described some aspect of the balance between proliferation and apoptosis, the stem cell differentiation and the positional instructions required all of them to properly regenerate any structure and produce the tissue turn over required during the normal homeostasis of the animals.
To study the balance between proliferation and apoptosis, we were focused in the description of Krüppel-like factor 10/11, which in other organisms is also involved in these mechanisms. Here we show that klf10/11 is required for the proper regulation of proliferation and apoptosis in regeneration and that they are essential for the correct remodelling of the organism structures, probably downstream c-Jun N-terminal kinase.
On the other hand, we have been focused on the study of the transcriptional complex Nuclear Factor Y in order to understand its role during differentiation events in planarian. We have shown that planarian NF-Y is essential for regeneration and homeostasis and that its inhibition generates neoblast accumulation and absence of epidermal progenitors which demonstrates that NF-Y is involved in the early differentiation of epidermal lineage progenitors.
Finally, the positional instructions which are essential for the correct positioning of cells and organs during regeneration and homeostasis have been studied. Here, we have been focused in the control of the medio-lateral organization of the central nervous system in planarian, where Wnt5 and Slit play an essential role. Wnt5, Slit and their receptors create a self-regulatory system to establish the medio-lateral pattern in planarians which guide the CNS to be positioned in this axisAlgunos animales tienen habilidades regenerativas increíbles, las cuales han mantenido a los investigadores fascinados durante décadas. Cómo estos animales son capaces de regenerar partes perdidas y recuperar los tejidos dañados podría dar a los investigadores claves en el campo de la medicina regenerativa. Aquí, nosotros usamos la planaria Schmidtea mediterránea, una especie que es capaz de regenerar completamente cada parte perdida, para entender más profundamente el proceso de regeneración y recambio tisular. Ambos procesos comparten varios mecanismos los cuales son esenciales para su correcto desarrollo. En esta Tesis, describimos algunos aspectos del balance entre la proliferación y la apoptosis, la diferenciación de células madre y las instrucciones posicionales, requeridas todos ellos para regenerar cualquier estructura y producir el recambio tisular requerido durante la homeostasis normal de los animales. Para estudiar el balance entre la proliferación y la apoptosis, nos hemos centrado en la descripción del factor Krüppel-like 10/11, el cual se ha relacionado con estos procesos en otros organismos. Aquí hemos visto que, klf10/11 se requiere durante la regeneración para la correcta regulación de la proliferación y de la apoptosis y que es necesario para el correcto remodelaje de las estructuras del organismo, probablemente aguas abajo de la kinasa c-Jun N-terminal. Por otra parte, nos hemos centrado en el estudio del complejo transcripcional Nuclear Factor Y para así comprender su papel durante los eventos de diferenciación en la planaria. Hemos visto que el NF-Y presente en planaria es esencial para la regeneración y homeostasis y que su inhibición produce la acumulación de neoblastos y la pérdida de progenitores epidérmicos, lo cual demuestra que NF-Y está involucrado en la diferenciación temprana de los progenitores tempranos epidérmicos. Finalmente, se han estudiado las instrucciones posicionales, las cuales son esenciales para el correcto posicionamiento de las células y órganos durante la regeneración y homeostasis. Aquí, nos hemos centrado en el control de la organización medio-lateral del sistema nervioso central en la planaria, donde Wnt5 y Slit juegan un papel esencial. Wnt5, Slit y sus receptores crean un sistema auto-regulativo para establecer el patrón medio-lateral en las planarias, el cual guía al SNC para ser posicionado en este eje.
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Arseni, Varvara. « MicroRNAs and the canonical microRNA biogenesis pathway in the planarian Schmidtea mediterranea ». Thesis, University of Nottingham, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581999.
Texte intégralRésumé :
miRNAs are an important class of small non-protein coding RNAs whose specific functions in animals are rapidly being elucidated. miRNAs regulate the expression of many animal genes by post-transcriptional gene silencing and play vital roles in stem cell maintenance, differentiation and apoptosis. In this study, planarians were used as a model system in order to study whether miRNAs have a regulatory role in their stem cell dynamics. Planarians are well known for their remarkable regenerative ability and their amazing capacity for constant re-patterning owing to a population of somatic pluripotent stem cells known as neoblasts. In particular, the aim of the study was to investigate the regulatory role miRNAs may have in planarian stem cell self renewal, proliferation and differentiation. Recently, the differential spatial patterns of expression of miRNAs in whole and regenerating planarians have been characterized by in situ hybridization to nascent miRNA transcripts. These miRNA expression patterns were the first to be determined for a Lophotrocozoan animal. The expression patterns of 42 miRNAs in adult planarians have been characterized, constituting a complete range of tissue specific expression patterns. The majority of planarian miRNAs were expressed either in areas where stem cells (neoblasts) are located and/or in the nervous system. Some miRNAs were definitively expressed in stem cells and dividing cells and moreover miRNAs were found to be expressed in germ stem cells of the sexual strain. Taken the facts that cellular proliferation and differentiation must be controlled during planarian regeneration and tissue homeostasis as well as that miRNAs have been implicated in the control stem cell functions in other organisms, aim of this study was to disrupt the canonical miRNA biosynthesis pathway. In that way, information about the global impact of miRNA regulation in planarian regeneration and tissue homeostasis would be gained.
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Guo, Longhua. « Establishing the foundations for genetic analysis in the sexual planarian Schmidtea mediterranea ». Thesis, The University of Utah, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10159126.
Texte intégralRésumé :
We propose to establish a free-living, fresh water flatworm species from the superphylum Lophotrochozoa, Schmidtea mediterranea, to be a genetic model system. S. mediterranea has been vigorously investigated as a powerful system to study adult stem cells and organ regeneration. Its sexual biotype has also been established as a system to understand the inductive mode of germ cell formation that is broadly shared by a lot of species including mammals. However, little is known about the sexual reproduction and genetics in this organism, which limited the availability of genetic approaches. As the sexual planarian is found scattered but with relative abundance in Sardinia, its natural history also presents us the opportunity to study inbreeding?s effect on genetic variability and species survival. Therefore, to study sexual reproduction and genetic inheritance in S. mediterranea will provide us unique opportunities to understand whole body regeneration, inductive germ cell formation, and inbreeding. In this dissertation, progresses in the establishment of the foundation for genetic analysis in S. mediterranea were presented. Though a simultaneous hermaphrodite, the anatomical and genotyping studies concluded that S. mediterranea cross-fertilize. One worm (line S2) was inbred for 10 generations by taking one progeny from each generation and crossing this individual to its regenerated clones. Whole genome sequencing of four different generations in this inbreeding pedigree revealed ~300Mb of the genome maintained their heterozygosity. Further sequencing analysis of the male and female gametes found these regions had low recombination rates, and maintained as two haplotypes (J-/V- haplotypes). Failure of gametes of the same haplotype to form progeny is unlikely due to embryonic lethality as the arrested embryos were significantly less than hatchlings. Additional analysis of two lines (D5D/D5I) with 90% of these regions homozygous as the J-haplotype suggested failure in fertilization between gametes of the same haplotype. Hence, we propose that haplotype incompatibility is the driving mechanisms to maintain genome heterozygosity in the planarian genome. Understanding of the genetic strategies in S. mediterranea will help the development of genetic approaches to study regeneration and germ cell specification. Our findings also suggest S. mediterranea can be a model system to study the evolution of sex and gamete incompatibility.
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Magley, Robert Alan. « A planarian Tau Tubulin Kinase homolog is required for spermatogenesis and epithelial ciliogenesis ». Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright153546883070243.
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Domingues, Vasco Filipe de Castro. « Toxicity of silver nanoparticles and silver nitrate to the freshwater planarian Dugesia tigrina ». Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/17016.
Texte intégralRésumé :
Mestrado em Toxicologia e EcotoxicologiaAtualmente, as nanopartículas de prata (AgNP) são bastante utilizadas em vários produtos devido às suas propriedades únicas e excecionais, nomeadamente a sua potente atividade antibacteriana. Algumas das suas aplicações comuns são em têxteis, produtos cosméticos e tintas. Deste modo, é esperada a presença de AgNP nos sistemas aquáticos. Tendo isto em consideração, o objetivo deste trabalho é descrever os efeitos tóxicos de AgNP de diferentes tamanhos, e comparar estes efeitos com os induzidos pela exposição a AgNO3 usando as características comportamentais das planárias da espécie Dugesia tigrina. Foram efetuados testes de exposição aguda (96 h) e testes de exposição crónica (8 dias) onde foram avaliados parâmetros como a sobrevivência, a locomoção, alimentação e regeneração cefálica. Foram selecionadas AgNP de diferentes tamanhos (AgNP de 10-25 nm e AgNP 3-8 nm) e comparados os efeitos com os da exposição a AgNO3, de modo a analisar se a toxicidade tem origem na libertação de iões Ag ou se é devida às propriedades das diferentes nanopartículas. Os resultados mostraram que os valores de LC50 para as 24, 48, 72 e 96 h não variaram ao longo do tempo para AgNP (10-25 nm) (76.62 μg L-1) e para AgNO3 (109.1 μg L-1). As planárias experienciaram nas primeiras 24 h várias alterações morfológicas na zona da cabeça como aurículas suprimidas e principalmente dissolução da cabeça. Estes efeitos notaram-se principalmente na AgNP (10-25 nm) e AgNO3. Em relação à exposição crónica, as planárias apresentaram uma redução significativa na locomoção e na alimentação na exposição a todas as nanopartículas estudadas, sendo estes parâmetros os mais sensíveis para D. tigrina. Relativamente à capacidade de regeneração não houve efeitos significativos à exposição a Ag. A fonte de toxicidade pode estar relacionada com as propriedades das AgNP que interferem com o sistema nervoso das planárias, causando a sua morte. Este estudo demonstrou que as planárias são um organismo adequado para estudos ecotoxicológicos comportamentais e devem ser considerados em metodologias de avaliação de risco ambiental.
Currently, silver nanoparticles (AgNP) are widely used in several products because of their unique and exceptional properties, particularly its potent antibacterial activity. Thus, AgNP are very often applied in textiles, cosmetics and paints. Under those circumstances, AgNP is expected to be present in aquatic systems. Taking this into consideration, the objective of the present work is to describe the toxicity of AgNP of different sizes and compare to the toxicity from AgNO3 exposure using behavioral endpoints of the planarian Dugesia tigrina. Acute exposure tests (96 h) and chronic exposure tests (8 days) were performed, in which parameters such as survival, locomotion, feeding and regeneration were evaluated. Therefore, AgNP of different sizes were selected (AgNP of 10-25 nm and AgNP 3-8 nm) and effects from exposure were compared to those from AgNO3, in order to analyze whether the source of toxicity was originated by release the ionic form of Ag or related to the inherent properties of nanoparticles. The results showed that LC50 values at 24, 48, 72 and 96 h were equal over time for AgNP (10-25 nm) (76.62 μg L-1) and for AgNO3 (109.1 μg L -1). In the first 24 h, planarians experienced several morphological alterations at the head region such as suppressed auricles and mainly head dissolution. These effects were noted mainly in AgNP (10-25 nm) and AgNO3 exposures. Regarding chronic exposure, planarians presented a significant reduction in locomotion and feeding activity upon both AgNP exposures. These endpoints revealed to be the most sensitive to D. tigrina. There were no significant effects on the regeneration test. The source of toxicity may be related to the properties of AgNP that interfere with nervous system of planarians consequently causing their death. This study demonstrated that planarians are an adequate organism for behavioural ecotoxicological studies and should be considered in environmental risk assessment methodologies.
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Sayson, Steven Gobinsing. « Investigation of Exoribonuclease-1 function in regulation of stem cells during planarian regeneration ». Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1454426814.
Texte intégral
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Curry, Haley Nicole. « Characterization of a Conserved Transient Receptor Potential Channel Supporting Spermatogenesis in Planarian Flatworms ». Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1589976835122505.
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Christman, Donovan. « A Planarian Kinesin Associated Protein 3 Homolog is Required for Spermatogenesis and Ciliogenesis ». Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright159016711952782.
Texte intégral
22
Murugan, Nirosha J. « PHYSICAL AND CHEMICAL CHANGES IN PLANARIAN AND NON-LIVING AQUEOUS SYSTEMS FROM EXPOSURE TO TEMPORALLY PATTERNED MAGNETIC FIELDS ». Thesis, Laurentian University of Sudbury, 2013. https://zone.biblio.laurentian.ca/dspace/handle/10219/2125.
Texte intégralRésumé :
Planarian maintained in spring water and exposed for two hours to temporally patterned, weak (1 to 5 μT) magnetic field in the dark displayed diminished mobility that simulated the effects of morphine and enhanced this effect at concentrations associated with receptor subtypes. A single (5 hr) exposure to this same pattern following several days of exposure to a very complex patterned field in darkness dissolved the planarian and was associated with an expansion of their volume. Spectral power density analyses of direct measurements of the spring water only following exposure to this field in darkness showed emission spectra that were displayed from control conditions by ~10 nm and associated with an energy increment of ~10-20 J. This value is an intrinsic solution for the physical properties of the water molecule. “Shielding” the exposed water with plastic, aluminum foil or copper foil indicated that only the latter eliminated a powerful spike in photon emission around 280 nm. Continuous measurement of pH indicated that the slow shift towards alkalinity over 12 hours of exposure was associated with enhanced transient pH shifts of .02 units with typical durations between 20 and 40 ms. These results indicate that the appropriately patterned and amplitude of magnetic field that affects water directly could mediate some of the powerful effects displayed by biological aquatic systems.
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Tran, Thao Anh [Verfasser], et Heiko [Akademischer Betreuer] Zimmermann. « Characterization of the ground state pluripotency in planarian / Thao Anh Tran ; Betreuer : Heiko Zimmermann ». Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://d-nb.info/1196089817/34.
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Wang, Irving E. « Identification of pluripotent stem cells and characterization of glia in the planarian Schmidtea mediterranea ». Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92648.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Given their regenerative capacity, the planarian Schmidtea mediterranea has emerged as a model system for the study of stem cell biology, tissue specification, and axis formation. Many aspects of the regenerative machinery have yet to be characterized. Although it is known that neoblasts, the population of all proliferative cells in the adult planarian, are the source of new tissue during regeneration, it is unknown whether neoblasts consist of multiple subpopulations of lineage-restricted multipotent stem cells or if there exists a pluripotent stem cell type. We developed two methods for performing clonal analysis to determine the potential of neoblasts: sublethal irradiation and single-cell transplantation. Colonies consisting of both self-renewed neoblasts expressing stem cell markers and differentiated cells expressing specialized tissue markers from single cells that we have termed clonogenic neoblasts. These cells are capable of generating all differentiated cell types in the adult animal and restoring regeneration in hosts where endogenous neoblasts have been ablated. These findings provide insight into the overall process of regeneration and the regulation of pluripotent adult stem cells during regeneration. Regeneration and homeostasis, the gradual turnover and replacement of cells in the adult planarian, both require the formation of new cells and signaling pathways to control their specification and function. The Hedgehog signaling pathway has been implicated in anterior-posterior polarity specification, but no role in planarian nervous system regeneration has been described despite that hedgehog is expressed in neurons in the brain. Although Hedgehog signaling is critical for central nervous system development in vertebrates and Drosophila, our data indicate that it is not involved in patterning the planarian brain. Instead, Hedgehog signaling regulates gene expression in a cell type identified as planarian glia from its localization to the axon-rich neuropil, expression of planarian orthologs of astrocyte genes, and branching morphology in close association with neurons. Evidence of both the existence of planarian glia and their regulation by Hedgehog signaling offers the opportunity to dissect glial cell biology in a highly regenerative model organism and understand the evolution of the cell type.
by Irving E. Wang.
Ph. D.
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Wagner, Daniel Elger. « Cellular and genetic mechanisms of new tissue production in the regenerating planarian Schmidtea mediterranea ». Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70394.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references.
Regeneration of missing body parts is biologically fascinating, yet poorly understood. Many instances of regeneration, such as the replacement of amphibian limbs or planarian heads, require both a source for new cellular material as well as mechanisms to specify, differentiate, and pattern the regenerate. The planarian Schmidtea mediterranea is a classic system for studies of regenerative biology in which proliferating cells known as "neoblasts" provide the source of new cellular material for regeneration. Stem cells that might be present within the neoblast population, however, have not yet been defined. Such cells could therefore be either pluripotent or, alternatively, a heterogeneous collection of lineage-restricted cell types. In order to distinguish these models experimentally, methods for clonal analysis were developed here and used to assess descendants of individual neoblasts. Individual cells, termed "Clonogenic Neoblasts" (cNeoblasts) were identified that gave rise to large descendant cell colonies in vivo. Individual cNeoblasts generate descendants spanning multiple germ layers and, in single cell transplantation experiments, all cells of the adult body. These data indicate that adult pluripotent stem cells (cNeoblasts) are the source of new tissue for planarian regeneration. Despite a sequenced genome and the availability of RNAi, the genetic basis for stem cell regulation in Schmidtea mediterranea has remained largely unexplored. Using microarrays, a genome-scale approach was taken to identify and characterize genetic factors specifically expressed in proliferating cells (neoblasts) of adult planarians. Genes identified by microarray were RNAi screened using quantitative assays (developed here) for expansion and differentiation of cNeoblast descendants. Several genes encoding proteins with conserved roles in germ cell biology (e.g. Vasa) and chromatin regulation (e.g. Polycomb proteins Ezh, Sz12, and Eed) were identified as required for proliferative cell expansion and/or differentiation, along with additional genes encoding three zinc finger proteins, two transcription factors, and two candidate RNA-binding proteins. These experiments suggest that cNeoblast regulation involves mechanisms shared with germ cells and embryonic stem cells, and provide a powerful framework for future investigations of planarian stem cell function.
by Daniel Elger Wagner.
Ph.D.
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Li, Dayan J. « Establishment and maintenance of pattern at the ends of the planarian anterior-posterior axis ». Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111302.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references.
How cellular and molecular processes are orchestrated to generate complex tissues and anatomical patterns is a longstanding question in biology. Planarians, flatworms capable of remarkable whole-body regeneration, are well suited for the study of patterning. They are adept at establishing pattern in new tissues during regeneration and maintaining pattern of existing tissues during homeostasis. We focused our study of patterning along the planarian anterior-posterior (AP) axis spanning the head and the tail. Located at the ends of the AP axis are the anterior and posterior poles. As putative organizers, the anterior and posterior poles are regions defined by their expression of genes required for head and tail patterning, respectively. Using transplantation, we tested the organizing activity of the head tip region containing the anterior pole and demonstrated its ability to induce outgrowths containing a new AP axis and a midline. Furthermore, we studied the formation of the anterior pole during regeneration and determined that its location is set by three landmarks in pre-existing tissue - a polarized AP axis, the midline, and the dorsal-ventral median plane. By organizing regenerating tissue around a location determined by preexisting tissue, the anterior pole links existing positional cues to the establishment of new pattern. To better understand pole function, we characterized the anterior and posterior pole transcriptomes by RNA sequencing. We identified several new genes highly expressed in the poles, including ones encoding transcription factors, cell surface receptors, and a secreted factor produced by both poles. Among them was nr4A, a nuclear receptor gene predominantly expressed in the body-wall muscle and found to regulate the expression of other muscle-enriched genes. Inhibition of nr4A during homeostasis resulted in both head and tail patterning defects characterized by a posterior shift of the anterior pole and an anterior shift of the posterior pole. This was accompanied by similar changes in the expression domains of head and tail patterning genes, and was followed by loss of muscle fibers at the head tip and the appearance of ectopic differentiated tissues normally restricted to the head and tail tip periphery. These results identified nr4A as a new planarian patterning gene that maintains head and tail identities, as well as anterior and posterior pole locations, at the ends of the planarian AP axis.
by Dayan J. Li.
Ph. D.
27
Tran, Thao Anh Verfasser], et Heiko [Akademischer Betreuer] [Zimmermann. « Characterization of the ground state pluripotency in planarian / Thao Anh Tran ; Betreuer : Heiko Zimmermann ». Saarbrücken : Saarländische Universitäts- und Landesbibliothek, 2019. http://nbn-resolving.de/urn:nbn:de:bsz:291--ds-283706.
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Hwang, Byulnim. « Two distinct roles of the yorkie/yap gene during homeostasis in the planarian Dugesia japonica ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199147.
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Mihaylova, Yuliana. « Epigenetic control of planarian stem cell potency limits stem activity and accurately defines differentiation programs ». Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/32929/.
Texte intégralRésumé :
Planarian flatworms are gaining popularity in regenerative medicine research due to the fact that they have unparalleled regeneration capacity. Their tissue recovery abilities are dependent on a pool of adult stem cells (neoblasts). Studies in the recent years have shown that epigenetic mechanisms have an important role in neoblasts’ self-renewal and differentiation properties. This thesis focuses on the study of trithorax-related genes and their function in neoblast regulation. Despite the fact that mammalian trithorax-related genes Mll3 and Mll4 are among the most frequently mutated genes in cancer, trithorax-related genes are the least well-studies members of the trithorax gene group (TrxG) of histone modifiers. The current study traced the evolutionary history of trithorax-related genes and concluded that they have undergone a number of independent gene fission events across phyla. In planarians, there are three partial orthologue of the mammalian Mll3 and Mll4 genes – Smed-LPT (corresponding to the N-terminus of Mll3/4), Smed-trr-1 and Smed-trr-2 (both corresponding to the C-terminus of Mll3/4). The three planarian trithorax-related genes are expressed in stem cells and control neoblast differentiation down certain lineages (brain, gut, eyes, pharynx, epidermis). Down-regulation of Smed-LPT results in hyperproliferation of stem cells, leading to tumour-like outgrowth formation. It was shown that trithorax-related genes’ function in stem cell regulation correlates with histone modification changes, specifically alterations in H3K4me1, H3K4me3 and H3K27me3. Future studies will focus on examining this correlation further via Next-Generation sequencing techniques.
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Shaffer, Traci R. « The Effects of Betadine®, Polyvinylpyrrolidone (PVP), and Iodine on Regeneration in the Planarian Dugesia tigrina ». Digital Commons @ East Tennessee State University, 2010. https://dc.etsu.edu/etd/2247.
Texte intégralRésumé :
The freshwater planarian has a great capacity to regenerate and is an ideal animal model in the study of stem cell and regeneration biology. In this study planarian regenerating new tails were exposed to nonlethal doses of Betadine®, Polyvinylpyrrolidone (PVP), and Iodine. Betadine® is a topical antiseptic commonly used in the healthcare setting and may have a detrimental effect on wound healing. PVP is linked to iodine to create povidone-iodine, the active ingredient in Betadine®. Initially, a preliminary test was performed on the worms to determine the nonlethal concentrations of these chemicals . After this nonlethal concentration was determined, tails were amputated and a designated number of worms were placed in the Betadine®, PVP, and Iodine solutions. Spring water was used as a control. This study determined that Betadine® and PVP showed no significant impact on regrowth rate and wound healing in the planarian, while Iodine did.
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Jipoulou, José Horacio Grau. « Relações filogenéticas entre os gêneros de Geoplaninae (Platyhelminthes, Tricladida) inferidas de caracteres morfológicos ». Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/41/41133/tde-12052010-103936/.
Texte intégralRésumé :
Este trabalho consiste em uma caracterização morfológica das espécies-tipo da maioria dos gêneros que compõem a subfamília Geoplaninae, e quatro espécies destinadas a servir como grupos externos (Pelmatoplanini, Anzoplanini, Caenoplanini, Bipaliinae). A estudo morfológico das espécies resultou em 69 caracteres morfológicos que foram inseridos em uma matriz de dados e preparados para análise filogenética. Quinze espécies adicionais de outros gêneros de Geoplaninae também foram incluídos na análise. Os resultados corroboram o monofiletismo da subfamília Geoplaninae. De acordo com a hipótese de Meixner, o clado formado pelos gêneros Enterosyringa e Xerapoa, que compartilha características morfológicas com espécies do grupo externo, é o grupo de irmãos de todas as demais espécies de Geoplaninae. Descobrimos que as características anatômicas do aparelho copulador, como a presença e o tipo de papila peniana mostraram possuir muitas reversões e não se mostraram filogeneticamente informativas. Caracteres do sistema muscular podem ser usados de forma mais efetiva para a definição de grupos taxonômicos dentro do Geoplaninae e como indicadores de suas relações evolutivas. Nenhum dos aspectos diagnóstico atuais de da Geoplaninae correspondeu a caracteres autopomórficos em nossa análise. Nossos resultados sugerem que vários gêneros de Geoplaninae representam grupos não naturais, i.e., Geoplana e Notogynaphallia, com alguns caracteres diagnósticos sendo homoplásicos.This work consists of a morphological characterization of the type species of most of the genera that compose Geoplaninae, and four species intended to serve as outgroups (Pelmatoplanini, Anzoplanini, Caenoplanini, Bipaliinae). The morphological study of the species resulted in 69 morphological characters that were entered into a data matrix and prepared for phylogenetic analysis. Fifteen additional species from other Geoplaninae genera were also included in the analysis. The results corroborate the monophyletic status of the subfamily Geoplaninae. According with Meixner\'s hypothesis, the clade formed by Enterosyringa and Xerapoa species, sharing morphological characteristics with outgroup species, is the sister group of all other Geoplaninae species. We found that anatomical features of the copulatory apparatus, such as the presence and type of penis papilla showed many reversions and were not phylogenetically informative. Characters of the muscular system can be used much better for defining taxonomic groups within the Geoplaninae and as indicators of their evolutionary relationships. None of the present diagnostic features of the Geoplaninae formed autapomorphic characters in our analysis. Our results suggest that several genera of Geoplaninae represent unnatural groups, viz., Geoplana and Notogynaphallia, with some diagnostic characters being homoplasic.
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Wenemoser, Danielle [Verfasser]. « Identification of mechanisms that govern regeneration initiation, using the planarian Schmidtea mediterranea as a model / Danielle Wenemoser ». Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1027815103/34.
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Stewart, Valerie I. « The biology of the terrestrial planarian Artioposthia triangulata (Dendy, 1894) and its genetic variation in colonized habitats ». Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241527.
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Pascual, Carreras Eudald. « Autonomous and non-autonomous regulation on planarian growth and regeneration : Smed-bls, canonical Wnt signalling and Fox family ». Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/668674.
Texte intégralRésumé :
Development requires an increment of cell growth and cell number, concomitant to a tightly control of cell differentiation. Thanks to cell communication, cells can be spatiotemporal patterned to acquire the required fate. Planarians are a unique model to study developmental processes due to their ability to regenerate and modulate their body size according to the nutrient availability. This body plasticity is based on the presence of pluripotent adult stem cells (neoblasts) and the continuous activation of the intercellular communication mechanisms. This active regulation of stem cells fate make them perfect models to study processes as growth, patterning, differentiation cell proliferation or cell death. In this thesis we have studied different molecular mechanisms that control planarian growth and pattern.
We have described a novel gene family, blitzschnell (bls), formed by de novo and taxonomically restricted genes, which control cell number trough the regulation of cell proliferation and cell death. Nutrient intake controls its expression suggesting that bls family have evolved in planarians as a mechanism by which to restrict cell number in nutrient-fluctuating environments. During growth and regeneration, planarians are not only able regulate their body and organ size accordingly but they also maintain a proper pattern. This regulation is mediated by different signalling centres that specify different regions along the 3 body axes (AP, DV and ML). Particularly, after an amputation, the anterior and the posterior planarian tips behave as organizers (signalling centre), specifying the fate of each planarian pole. The anterior organizer is defined by notum (a Wnt inhibitor) and the posterior by wnt1 expression. The inhibition of any of those elements leads to a shift in polarity. During the first hours of regeneration both notum and wnt1 are expressed in both poles, and it’s around 36 hours that their expression becomes restricted to their respective tip. To decipher the molecular interactions that restrict the expression of wnt1 to the posterior tip and confer the organizing activity we used genome wide approaches. ATAC-seq and RNA-seq analysis of regenerating wild-type and wnt1 (RNAi) planarians allowed the identification of specific Cis-Regulatory Elements (CREs) of posterior regeneration. We found that already at 12 hours of regeneration the accessible CREs in posterior and anterior blastemas have essentially changed, indicating that specific posterior chromatin changes induced by amputation occur much earlier than the formation of the organizers. Furthermore, we have identified specific transcription factors (TF) of the Otx and Fox families, which are enriched in posterior CREs. Particularly, pitx and foxG regulates wnt1+ cells and are essential for the specification of the posterior cells.
TFs regulate patterning events and developmental specification, particularly the Fox Family exerts crucial roles defining cell types of all germ cell layers or regulating cell cycle. Before this Thesis, poorly was known about the Fox family in Schmidtea mediterranea (Smed) neither in the Lophocotrozoan clade. In this study we have identified 27 Fox genes in Smed, classified in 13 families: A, At, C, D, E, G, L1t, QD, J1, N2/3, Nt, O and P. We have performed an extensive phylogenetic study of the family to understand the evolution of the Fox family in this clade. Furthermore, we have studied the sequence, expression and function of several planarian Fox genes.
Overall, we studied different molecular mechanisms that regulate planarian growth and regeneration, and that provide novel data concerning development and evolution.
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Collins, Erica Leighanne. « The Effect of Caffeine and Ethanol on Flatworm Regeneration ». Digital Commons @ East Tennessee State University, 2007. https://dc.etsu.edu/etd/2028.
Texte intégralRésumé :
Flatworms, or planarian, have a high potential for regeneration and have been used as a model to investigate regeneration and stem cell biology for over a century. Chemicals, temperature, and seasonal factors can influence planarian regeneration. Caffeine and ethanol are two widely used drugs and their effect on flatworm regeneration was evaluated in this experiment. Non-toxic levels of caffeine, a stimulant, and ethanol, a depressant, were determined. The tails of the flatworms were removed and the regeneration stage was analyzed every 3 days for 15 days to see the effect of these drugs alone and in combination on regeneration. For day 3 and day 6, there was a significant difference between the ethanol treatment and the other treatments (positive control, caffeine treatment, and combined treatment). The ethanol treatment showed a delay in the initiation of regeneration but caught up to the other treatments by day 15.
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Ribeiro, Alyson Rogério 1986. « Potencial do uso de planárias na avaliação de contaminantes ambientais=Potential use of planarians for environmental contaminants evaluation ». [s.n.], 2012. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267776.
Texte intégralRésumé :
Orientador: Gisela de Aragão UmbuzeiroDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Tecnologia
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Resumo: As planarias de água doce possuem vasta distribuição geográfica, plasticidade biologica, facilidade de cultivo em laboratório, sensibilidade a contaminantes diversos e capacidade regenerativa, por isso vem sendo utilizadas como organismos-teste em ensaios ecotoxicologicos. Porem, ainda não ha normatização internacional ou nacional que padronize esses ensaios. O objetivo deste trabalho foi verificar o potencial do uso de planarias de agua doce (Girardia tigrina) na avaliação de alguns contaminantes e amostras ambientais utilizando protocolos padronizados avaliando-se mortalidade e atraso na regeneração encefálica. Foram empregados 15 organismos por concentração-teste nos ensaios de mortalidade de filhotes (96h) e 20 planarias adultas regenerantes por concentração-teste nos ensaios de regeneração encefálica (120h). Avaliou-se cromo e zinco como substancias de referencia e empregou-se cobre, azo corante têxtil Disperse Red 1, herbicida atrazina, nanotubos de carbono de parede múltipla, alem de amostras da ETE Carioba e do Ribeirão dos Cristais. Carta controle com substancia de referencia foi realizada, sendo estabelecido um protocolo para o monitoramento da sensibilidade das culturas de G. trigrina. O zinco foi a substancia mais apropriada que o cromo, com a vantagem do ensaio de sensibilidade poder ser finalizado em 24h. Os métodos utilizados para realização do ensaio de regeneração encefálica e de mortalidade de filhotes foram eficazes para a observação de efeitos adversos das substancias analisadas. Todas as amostras testadas apresentaram toxicidade as planarias, exceto os nanotubos de carbono. Atraso na regeneração encefálica foi o endpoint mais sensível para os contaminantes avaliados. Os protocolos utilizados neste estudo podem ser utilizados como subsídios na elaboração futura de normas técnicas de testes ecotoxicologicos com planarias de agua doce
Abstract: Freshwater planarians are worldwide distributed, have biological plasticity and a unique body regenerative capacity. They are easily maintained under laboratorial conditions and are sensitive for several compounds. For these reasons they have been used in ecotoxicological testing although the lack of national or international guidelines. This research aimed to verify the potential use of freshwater planarians (Girardia tigrina) in mortality and regeneration delay endpoints to assess the toxicity of environmental contaminants using standardized protocols. The culture sensitivity of G. tigrina was monitored with zinc, which was the most suitable substance for this purpose, providing responses in only 24h. The adopted protocols for regeneration and mortality tests were efficient to assess the adverse effects of the chemical agents (copper, an azo textile dye, atrazine), carbon nanotubes and wastewater and water samples from Carioba WWTP and Cristais River. The regeneration test was the most sensitive endpoint and all analyzed substances showed toxicity for planarians, except carbon nanotubes. The methods adopted in this research can be used as basis for the development of a testing guideline using freshwater planarians
Mestrado
Tecnologia e Inovação
Mestre em Tecnologia
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Torre, Cédric. « Résistance des planaires à l'infection bactérienne : caractérisation de la mémoire immunitaire innée ». Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0528.
Texte intégralRésumé :
Mon travail de Thèse a porté sur la description de l’immunité antibactérienne de la planaire, et plus particulièrement la mémoire immunitaire innée.La mémoire immunitaire innée constitue une ligne de défense de l’hôte à la réinfection qui ne fait intervenir que des composants de l’immunité innée. Présente chez les vertébrés et les invertébrés, ces derniers constituent un modèle de choix car dépourvus d’immunité acquise. La planaire dispose d’une mémoire immunitaire innée envers S. aureus, qui, suite à une réinfection, se traduit par une élimination exacerbée. La déplétion des planaires en cellules souches et la greffe tissulaire ont permis de mettre en avant les cellules souches comme acteurs principaux de cette réponse immunitaire. Un criblage RNAi associé à un profilage transcriptomique ont fait ressortir des gènes en les hiérarchisant au sein d’une voie de signalisation impliquant un récepteur au peptidoglycane (pgrp-2), une histone méthyltransférase (setd8.1), et un mécanisme effecteur dans l’élimination bactérienne (p38 et morn2). Setd8.1, histone méthyltransférase, se placerait au cœur du processus en déposant des marques épi-génétiques sur des loci de l’ADN, garantissant l’expression accrue des gènes effecteurs suite à la réinfection. Ce mécanisme, décrit chez l’Homme, n’avait jusqu’alors jamais impliqué des cellules souches, ni ce type d’histone méthyltransférase comme acteurs dans la mémoire immunitaire innée.Collectivement, l’investigation du système immunitaire de la planaire a permis la découverte de mécanismes de défense antibactérienne inédits, dont le transfert à l’Homme pourrait compléter l’approche actuelle du traitement des maladies infectieusesMy Thesis work has focused on the description of the planarian antibacterial immunity, and more precisely the innate immune memory.The innate immune memory forms a host defense line to the reinfection which only involves components from innate immunity. Present in vertebrates and invertebrates, invertebrates are a model of choice because devoid of acquired immunity. The planarian has an innate immune memory against S. aureus, which, after a reinfection, displays an exacerbated elimination. The depletion of stem cells from planarians and tissue graft highlighted stem cells as the main actors of this immune response. An RNAi screening combined with a transcriptomic profiling brought out genes and classified them within a signaling pathway involving a peptido-glycan receptor (pgrp-2), a histone methyltransferase (setd8.1), and an effector mechanism of the bacterial elimination (p38 and morn2). Setd8.1, histone methyltransferase, would be the core of the process putting epigenetic marks on DNA loci, ensuring the increased expression of effector genes after reinfection. This mechanism, described in humans, has neither involved stem cells, nor this type of histone methyltransferase as actors in the innate immune memory.Collectively, the investigation of the planarian immune system allowed the discovery of new antibacterial defense mechanisms, and transferring it to humans could complete the actual approach of the infectious disease treatment
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Fowler, Joe. « Unlabled Level Planarity ». Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195812.
Texte intégralRésumé :
Consider a graph G with vertex set V in which each of the n vertices is assigned a number from the set {1, ..., k} for some positive integer k. This assignment phi is a labeling if all k numbers are used. If phi does not assign adjacent vertices the same label, then phi partitions V into k levels. In a level drawing, the y-coordinate of each vertex matches its label and the edges are drawn strictly y-monotone. This leads to level drawings in the xy-plane where all vertices with label j lie along the line lj = {(x, j) : x in Reals} and where each edge crosses any of the k horizontal lines lj for j in [1..k] at most once. A graph with such a labeling forms a level graph and is level planar if it has a level drawing without crossings.We first consider the class of level trees that are level planar regardless of their labeling. We call such trees unlabeled level planar (ULP). We describe which trees are ULP and provide linear-time level planar drawing algorithms for any labeling. We characterize ULP trees in terms of two forbidden subdivisions so that any other tree must contain a subtree homeomorphic to one of these. We also provide linear-time recognition algorithms for ULP trees. We then extend this characterization to all ULP graphs with five additional forbidden subdivisions, and provide linear-time recogntion and drawing algorithms for any given labeling.
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Furlan, Alan. « Laserspektroskoppie von Edelgasclustern mit planaren und nicht-planaren Aromaten / ». [S.l : s.n.], 1993. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
Texte intégral
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Sousa, Nidia de. « Role of the Hippo pathway in planarians ». Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/406086.
Texte intégralRésumé :
A successful cell renewal, which occurs throughout the life of an organism, relies on multiple events, including proliferation and differentiation of progenitor cell populations, and death of unnecessary cells. Out of the multiple molecular mechanisms involved in the control of cellular renewal, the Hippo signaling pathway currently appears as a hub. Although it was first identified as a key regulator of organ size through the control of cell death and proliferation, growing evidence suggests that it also plays pivotal roles in coordinating stem cell maintenance, cell differentiation, cell-fate decisions and cell survival.
To further understand the role of the Hippo pathway in driving adult cellular renewal and, specifically, in promoting cellular sternness, we studied its function in planarians. Due to the presence of a population of pluripotent adult stem cells (neoblasts), planarians have the ability to constantly grow and degrow depending on food availability, and to regenerate any missing body part within a few days. This active and continuous regulation of the stem cell and post-mitotic cell compartments makes planarians an ideal ' in vivo' context to gain an integrated view of the different events underlying homeostatic cell renewal and tissue regeneration.
Here, we address whether downregulation of Hippo signaling exerts its sternness promoting function by increasing the proliferation of resident stem cells or promoting cell dedifferentiation. We show that inhibition of Smed-hippo (to simplify, hippo) in planarians reduces apoptotic activity and increases mitotic rates. However, this imbalance between cell death and mitotic activity does not lead to an increase in planarian body size or cell number, since hippo (RNAi) does not increase the number of cycling cells but blocks mitotic exit. hippo (RNAi) animals develop overgrowths and extensive regions composed of undifferentiated cells, accompanied by a general decrease in the number of differentiated cells throughout their body. A detailed study of the epidermal lineage reveals that hippo is required to determine the hierarchical transitions required for proper epidermal differentiation, from epidermal-restricted
stem cells to differentiated epidermal cells. We also demonstrate that hippo is required to maintain the differentiated state in planarian cells, since hippo inhibition promotes dedifferentiation of post-mitotic cells. Overall, these results in di cate that thE overgrowths and undifferentiated regions observed after hippo inhibition in planarians are not caused by the unbalance between cell death and proliferation but to the inability of cells to reach and maintain the appropriate fate.
Furthermore, during this study we demonstrate that the Hippo-Yki signaling cascade is conserved in planarians and plays a role in cell differentiation during planarian regeneration. We further show the conservation of the up-stream regulators of the Hippo pathway in planarians since the inhibition of Hippo up-stream regulators, as lg/- 2, phenocopies the hippo (RNAi) phenotype. Transcriptomic analysis of hippo (RNAi) animals allowed the identification of several putative Hippo pathway targets in planarians, which silencing reproduces the formation of overgrowths.
Overall, we propose an essential role for Hippo signaling in restricting cell plasticity and thus in preventing tumoral transformation.La renovación celular, que tiene lugar durante toda la vida en los organismos adultos, depende de multiples eventos, incluyendo el control de la proliferación, la diferenciación de las celulas progenitoras y la muerte de células innecesarias. La vía de señalización de Hippo ejerce un papel central en el control de todos estos procesos. A pesar de haber sido primeramente identificada como una vía reguladora clave en el control del tamaño de los órganos a través de la regulación de la proliferación y la muerte, evidencias recientes sugieren que esta vía puede estar también involucrada en el mantenimiento de las células madre, en la diferenciación celular, en el mantenimiento del estado diferenciado y en la supervivencia de las células. Para profundizar en el conocimiento del papel de la vía de Hippo durante la renovación celular en tejidos adultos, específicamente en su función reguladora del estado pluripotente de las células, abordamos su estudio en planarias. Debido a la presencia de una población de células pluripotentes adultas, los neoblastos, las planarias poseen la capacidad de crecer y decrecer dependiendo de la disponibilidad de alimento, así como de regenerar cualquier parte de su cuerpo en apenas algunos días. Esta activa y continua regulación de las células madre y de los compartimentos postmitóticos convierte a las planarias en un contexto "in vivo" ideal para obtener una vision integrada de los diferentes mecanismos que controlan la renovación celular durante la homeostasis y la regeneración de los tejidos. En esta tesis hemos abordado la cuestión de si el silenciamiento de la vía de señalización de Hippo afecta a la promoción del estado indiferenciado, concretamente a través del control de la proliferación de células madre o bien promoviendo la desdiferenciación celular. Los resultados obtenidos demuestran que la inhibición de Smed-hippo (para simplificar, hippo) en planarias reduce la actividad apoptótica y aumenta los índices mitóticos. Sin embargo, este desequilibrio entre muerte celular y actividad mitótica no conduce al aumento del tamaño de las planarias ni al aumento del número de células. Uno de los motivos es que la inhibición de hippo no aumenta el numero de células que ciclan si no que bloquea la salida de mitosis. Sin embargo, aunque no hay un incremento en el numero de células, el silenciamiento de hippo produce la aparición de sobrecrecimientos, precedidos por la aparición de amplias regiones compuestas por células no diferen ciadas, yla reducción del numero de células diferenciadas en todo el animal. El estudio detallado del linaje epidermico, demuestra que hippo es necesario para determinar las transiciones jerarquicas requeridas para una correcta diferenciación de las células epidermicas. Ademas, demostramos que hippo es necesario para mantener el estado diferenciado de las células, ya que su inhibición promueve la desdiferen ciación de células postmitóticas. En conjunto, estos resultados indican que los sobrecrecimientos y regiones indiferenciadas observadas despues de la inhibición de hippo no son causados por el desequilibrio entre la muerte celular y la proliferac ión sino por la incapacidad de las células adquirir y mantener su estado diferenciado. Ademas, durante este estudio hemos demostrado que la cascada de sena lización Hippo-Yki esta conservada en planarias y desempeña un papel fundamental durante la regeneración. También hemos visto que los mecanismos reguladores "up-stream " de la via Hippo parecen estar conservados en planarias, ya que la inhibición de algunos elementos, como lg/2, fenocopia el fenotipo de los animales hippo (RNAi). A su vez, el analisis transcriptómico de los animales hippo (RNAi) ha permitido identificar genes diana de la vía Hippo en planarias. El silenciamiento de algunos de estos genes candidatos también promueve la aparición de sobrecrecimientos. Para finalizar, nuestros estudios nos permiten proponer que el papel principal de Hippo en las planarias es restringir la plasticidad celular y así prevenir la transformación tumoral.
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LoCascio, Samuel Alexander. « Mechanisms of tissue-specific regeneration in planarians ». Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/113952.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references.
How animals establish and maintain the sizes of myriad tissues and organs in tight proportion to one another is a fundamental question of developmental biology. Planarian flatworms regenerate from diverse injuries, in each case precisely restoring body parts to their appropriate proportions. Underlying this ability is a pluripotent population of dividing cells called neoblasts, which are required for homeostatic maintenance and regeneration of all planarian tissues. Whether neoblasts restore proportion by sensing and responding to the presence or absence of specific tissues during regeneration is unknown. We used the planarian eye lineage to address this problem. Following decapitation, neoblasts normally give rise to a large number of eye progenitors, facilitating eye regeneration. Remarkably, we found that eye absence alone was not sufficient to induce this response. Tissue-specific eye regeneration was achieved by homeostatic eye progenitor production accompanied by a decreased rate of cell death specifically in the regenerating eye. Conversely, large head wounds were sufficient to increase eye progenitors, even in the presence of intact eyes. Therefore, eye absence is not sufficient or necessary for neoblasts to increase eye progenitor production. Our findings suggest a "target-blind" model for planarian regeneration in which progenitor production by neoblasts does not depend on feedback from the presence or absence of specific target tissues to be regenerated.
by Samuel Alexander LoCascio.
Ph. D.
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Hayer, Matthias. « Testing planarity in linear time ». Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30483.
Texte intégral
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Bachmaier, Christian. « Circle planarity of level graphs ». [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=973953985.
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Estrella, Balderrama Alejandro. « Simultaneous Embedding and Level Planarity ». Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/195738.
Texte intégralRésumé :
Graphs are a common model for representing information consisting of a set of objects or entities and a set of connections or relations between them. Graph Drawing is concerned with the automatic visualization of graphs in order to make the information useful. That is, a good drawing should be helpful in the application domain where it is used by capturing the relationships in the underlying data. We consider two important problems in automated graph drawing: simultaneous embedding and level planarity. Simultaneous embedding is the problem of drawing multiple graphs while maintaining the readability of each graph independently and preserving the mental map when going from one graph to another. In this case, each graph has the same vertex set (same entities) but different edge sets (different relationships). Level planarity arises in the layout of graphs that contain hierarchical relationships. When drawing graphs in the plane, this translates to a restricted form of planarity where the vertical order of the entities is pre-determined. We consider the computational complexity of the simultaneous embedding problem. In particular, we show that in its generality the simultaneous embedding problem is NP-hard if the edges are drawn as straight-lines. We present algorithms for drawing graphs on predetermined levels, which allow the simultaneous embedding of restricted types of graphs, such as outerplanar graphs, trees and paths. Finally, our practical contribution is a tool that implements known and novel algorithms related to simultaneous embedding and level planarity and can be used both as a visualization software and as an aid to study theoretical problems.
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Taylor, Martyn G. « Planarity testing by path addition ». Thesis, University of Kent, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580367.
Texte intégralRésumé :
The first linear-time planarity testing algorithm was developed in 1974 by Hopcroft and Tarjan (H&T) [32] using a method to split a biconnected graph up into edge disjoint paths and then sequentially embed them to test for planarity (a path addition method). Shortly afterwards Booth and Leuker [5] developed an alternative vertex addition linear-time planarity test, based on the earlier work of Lempel, Evan and Cederbaum [47], using a new PQ-Tree data structure. Since then there have been many developments in PQ- Tree vertex addition (and related PC-Tree edge addition) methods including authors such as: Chiba et al. [14]; Shih & Hsu [35, 69]; Boyer and Myrvold [10, 11]; and Haeupler and Tarjan [29]. In comparison, path addition has changed very little from the original algorithm. In 1984, Williamson [84] showed how H&T's algorithm can be extended to find Kuratowski sub-graphs in the event of a non-planar graph; and, in 1993, Mehlhorn, Mutzel and Naher [53] produced an implementation (in C) of H&T's algorithm and extended it to create a planar embedding of a graph. This has remained the state-of-the-art in path addition algorithms for over a decade. Recently", de Fraysseix formulated an algorithm [15, 17], based on Tremaux Trees and a characterisation of planarity by W. Wu [87]; this may prove to be a highly optimised version of H&T's algorithm but is difficult to definitively prove as only an outline of its planarity testing phase is provided. These authors represent the majority of the work on path addition methods of planarity testing and embedding; indicating that it receives little attention compared to vertex or edge addition methods This thesis attempts to reinvigorate the field of path addition and demonstrates: • How Trernaux Trees, which allow undirected connected graphs to be represented as a simple partial order relationship are fundamentally related to H&T-‘^planarity testing algorithm and includes some related invariant properties of these trees; • That the restriction on H&T's planarity testing algorithm to test undirected biconnected graphs can be relaxed to undirected connected graphs; • How to generate all possible embeddings of a biconnected component and how to extend this to generate all possible embeddings of separable graphs; and • Empirical Testing of various graph types and sizes to validate these results.
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Tassion, Vincent. « Planarité et Localité en Percolation ». Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2014. http://tel.archives-ouvertes.fr/tel-01061007.
Texte intégralRésumé :
Cette thèse s'inscrit dans l'étude mathématique de la percolation, qui regroupe une famille de modèles présentant une transition de phase. Des avancées majeures au cours des quinze dernières années, notamment l'invention du SLE et la preuve de l'invariance conforme de la percolation de Bernoulli critique, nous permettent aujourd'hui d'avoir une image très complète de la percolation de Bernoulli sur le réseau triangulaire. Cependant, de nombreuses questions demeurent ouvertes, et ont motivé notre travail.La première d'entre elle est l'universalité de la percolation plane, qui affirme que les propriétés macroscopiques de la percolation plane critique ne devraient pas dépendre du réseau sous-jacent à sa définition. Nous montrons, dans le cadre de la percolation Divide and Color, un résultat qui va dans le sens de cette universalité et identifions, dans ce contexte, des phénomènes macroscopiques indépendants du réseau microscopique. Une version plus faible d'universalité est donnée par la théorie de Russo-Seymour-Welsh (RSW), et sa validité est connue pour la percolation de Bernoulli (sans dépendance) sur les réseaux plans suffisamment symétriques. Nous étudions de nouveaux arguments de type RSW pour des modèles de percolation avec dépendance. La deuxième question que nous avons abordée est celle de l'absence d'une composante connexe ouverte infinie au point critique, une question importante du point de vue physique, puisqu'elle traduit la continuité de la transition de phase. Dans deux travaux en collaboration avec Hugo Duminil-Copin et Vladas Sidoravicius, nous montrons que la transition de phase est continue pour la percolation de Bernoulli sur le graphe Z^2x{0,...,k}, et pour la percolation FK sur le réseau carré avec paramètre q inférieur ou égal à 4. Enfin, la dernière question qui nous a guidés est la localité du point critique : la donnée des boules de grands rayons d'un graphe suffit-elle à identifier avec une bonne précision la valeur du point critique? Dans un travail en collaboration avec Sébastien Martineau, nous répondons de manière affirmative à cette question dans le cadre des graphes de Cayley de groupes abéliens.
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Antunes, Michelle Bicalho. « Influência de variáveis ecológicas na ocorrência de planárias terrestres (Platyhelminthes : Tricladida : Terricola) em áreas de floresta ombrófila mista ». Universidade do Vale do Rio do Sinos, 2008. http://www.repositorio.jesuita.org.br/handle/UNISINOS/2304.
Texte intégralRésumé :
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A influência de fatores ecológicos na ocorrência de planárias terrestres é pouco conhecida. Estudos da estrutura de comunidades de planárias demonstram que estes organismos realizam seleção de habitat, apresentando baixa diversidade em habitats perturbados. O presente estudo objetiva testar se a ocorrência de planárias terrestres é influenciada por características do microhabitat, tais como características estruturais do ambiente, características edáficas e disponibilidade de presas. O estudo foi desenvolvido em duas áreas de Floresta Ombrófila Mista, na Floresta Nacional de São Francisco de Paula (FLONA-SFP), no Sul do Brasil. Em cada área, foi demarcada uma extensão de meio hectare, subdividido em quadrantes de 10m2. Em 100 parcelas distribuídas aleatoriamente, foram registradas a ocorrência e abundância de tricladidos, além de variáveis ecológicas. Foram analisadas seis características estruturais do ambiente (número de rochas, número e tamanho dos troncos e galhos caídos, altura do folhiço, densidade de a
In general, the influence of ecological factors on the occurrence of land planarians is poorly known. Studies on flatworm community structure verified that these organisms show habitat selection, exhibiting low diversity in disturbed habitats. The aim of this study is to test if the occurrence of land planarians are influenced by microhabitat traits, such as habitat structural traits, soil features and prey availability. The study was developed in two Araucaria Forest areas in the São Francisco de Paula National Forest (FLONA-SFP), southern Brazil. In each area, a grid of 0.5 hectares, subdivided in 10m2 plots, was established. In 100 randomly selected plots, the occurrence and abundance of each land planarian species were recorded. For each plot, we also recorded information on six habitat structural traits (number of stones, number and size of fallen trunks, shrub density, litter height, canopy openness), 21 soils features (physical and chemical variables), and 15 prey availability traits (total abundance o
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Tewari, Aneesha G. (Aneesha Ghanhi). « Pattern formation and essential responses for regeneration in planarians ». Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122068.
Texte intégralRésumé :
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
The fundamental requirements for regeneration are poorly understood. Planarians can robustly regenerate all tissues after injury, involving stem cells, patterning cues and a set of cellular and molecular responses collectively called the "missing tissue" or "regenerative" response. The missing tissue response has long been considered a fundamental requirement of planarian regeneration. follistatin, which encodes an extracellular Activin inhibitor, is required for the missing tissue response after head amputation, and for subsequent regeneration. We found that follistatin is required for the missing tissue response regardless of the wound context, but only causes regeneration failure after head amputation. This head regeneration failure involves follistatin-mediated regulation of Wnt signaling at wounds, and is not a consequence of a diminished missing tissue response.
We found that all tested contexts of regeneration, including head regeneration, could occur with a defective missing tissue response, however, at a slower pace. Our findings suggest that in the absence of major cellular and molecular programs induced by large injuries, regulation of wound-induced Wnt signaling to enable regenerative re-patterning along with continuous tissue turnover can mediate successful regeneration in essentially any wound context. Wnt signaling regulates primary body axis formation across the Metazoa, with high Wnt signaling specifying posterior identity. Whether a common Wnt-driven transcriptional program accomplishes this broad role is poorly understood. We identified genes acutely affected after Wnt signaling inhibition in the posterior of two regenerative species, the planarian Schmidtea mediterranea and the acoel Hofstenia miamia, which are separated by >550 million years of evolution.
Wnt signaling was found to maintain positional information in muscle and regional gene expression in multiple differentiated cell types. sp5, Hox genes, and Wnt pathway components are down-regulated rapidly after [beta]-catenin RNAi in both species. brachyury, a vertebrate Wnt target, also displays Wnt-dependent expression in Hofstenia. Planarian sp5 inhibits Wnt-dependent expression of trunk genes in the tail, promoting separate tail-trunk body domains. We propose that common regulation of a small gene set - Hox, sp5, and brachyury - might underlie the widespread utilization of Wnt signaling in primary axis patterning across the Bilateria.
by Aneesha G. Tewari.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Biology
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Mangione, Federica. « The Dachsous/Fat/Four-jointed Signalling Coordinates the Uniform Orientation of Planar Cell Alignement in the Drosophila Abdominal Epithelium ». Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/402714.
Texte intégralRésumé :
Within multicellular organism, mature tissues and organs reach high degrees of order in the arrangement of their constituent cells. During morphogenesis the emergence of long-range order is subjected to multiple and multilevel developmental constrains. Complex series of temporal and spatial instructions must be integrated to account for reproducible and stereotyped mature tissue arrangements. A remarkable example is given by mature epithelial monolayers were cells are ringed together in specific morphologies via cell-cell adhesion and show highly organized planar patterns. Cells in epithelial tissues acquire a precise planar geometry that is often, if not always, evenly aligned with the tissue axes.
Little is still known on the cellular mechanisms governing the axial orientation of cell arrangement and planar polarity.
The research presented in this Thesis addressed these issues through the analysis of the developing abdominal epithelium of Drosophila melanogaster.
We found that the abdominal epithelial cells reach their final arrangement within about 2 days of pupation. During this time, the abdominal epithelial tissue undergoes extensive morphogenesis by tissue expansion and cellular remodelling. During expansion, epithelial cells divide randomly relative to the tissue axis while migrating dorsally, while during remodelling cell adjust their final position within the plane of the epithelium while migrating anteriorly. When cell movements arrest, a stable arrangement of the cells within the plane of the segmental field is attained. At this time, epithelial cells are oriented and aligned among each other and throughout the tissues invariably in parallel to the A/P axis. We indicated as uniform orientation of planar cell alignment (PCA). We found that the axis orientation of PCA is evolving in a spatiotemporal precise manner along the A/P axis, and that this dynamic oriented behaviour was progressively modulated through expansion and remodelling. We found that the Dachsous/Fat/Four-jointed planar polarity pathway was specifically involved in the orientation of PCA. The steps followed to reach the axial orientation of PCA over developmental times correlates with the pattern of expression of the Dachsous/Fat/Four- jointed pathway. Such correlation was sustained by genetic interferences with the pathway components.
We found that both the dynamics of the axis orientation of PCA and the attainment of its uniformity along the A/P axis were disrupted rearrangements in dachsous, fat or four-jointed mutants. We further found that loss of the axial uniform orientation of PCA in these mutants is accompanied by an overall reduction in mutual cell alignment and in cell shape elongation. These effects were also sustained through local interference in the activity of the pathway through clonal analyses. Local changes in pathway components induce the mutant clones to minimize cell-cell contacts with surrounding wild-type cells, suggesting differential adhesive properties between dachsous, fat, four-jointed mutant cells and the rest of the tissue. Surprisingly, we found that this effect was also directional and that Dachsous has an instructive role in driving the axis orientation of PCA, possibly by regulating the Fat localization across the cells/tissue.
Therefore, from these findings, we propose that the Dachsous/Fat/Four-jointed pathway guide the orientation of PCA by favouring oriented cell-cell contact adhesiveness between abdominal epithelial cells. In particular, different adhesive properties imposed throughout the cell perimeter by Ds-Ft heterodimeric interaction at opposite edges of the cell might align epithelial cells changing and orienting their shape. Over time this biased interaction responding to the Dachsous gradient would be reinforced in response to the activity of Dachsous and Four-jointed onto Fat.En los organismos multicelulares, tejidos y órganos tienen una disposición altamente organizada de las células que los constituyen. En particular, los tejidos epiteliales están constituidos por células que se disponen de manera ordenada con respecto a los ejes del cuerpo aunque los mecanismos que gobiernan esta disposición ordenada son poco conocidos. En esta tesis nos hemos focalizado en el estudio de los mecanismos que guían la orientación del eje celular en el plano de un epitelio en crecimiento. El epitelio abdominal de Drosophila constituye un sistema modelo para estudiar in vivo las dinámicas celulares que ocurren a lo largo de la morfogénesis tisular. Nuestros resultados demuestran que las células del epitelio abdominal empiezan a orientarse progresivamente llegando a una disposición espacial altamente ordenada. En esta disposición las células demuestran una preferencia en alinearse con el eje anteroposterior del tejido dando lugar a una orientación uniforme del alineamiento celular. Por otro lado, hemos descubierto que la vía de señalización de Dachsous/Fat/Four-jointed está involucrada en guiar el eje de orientación celular con respecto a el eje anteroposterior. Nuestros datos indican que los patrones de expresión de los genes dachsous, fat y four-jointed juegan un papel clave para el correcto alineamiento celular con el eje anteroposterior. De hecho, mutaciones en estos genes alteran el alineamiento espacial y afectan la elongación celular. Además, alteraciones locales en la actividad de cada uno de estos genes indican que están involucrados en la modulación orientada de los contactos adhesivos entre células vecinas. En resumen, estos resultados sugieren que la vía de señalización de Dachsous/Fat/Four- jointed tiene un papel clave en el alcance de una orientación celular uniforme a lo largo del tejido abdominal y, posiblemente, en otros epitelios.
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Klein, Philip N. (Philip Nathan). « An efficient parallel algorithm for planarity ». Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/34303.
Texte intégralRésumé :
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: leaves 56-57.
by Philip Nathan Klein.
M.S.