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1
Kaptan, Damla. "Metabolic Transition in Caenorhabditis elegans Dauer Larva." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-223034.
Full textAbstract:
Under unfavorable environmental conditions Caenorhabditis elegans larvae enter a dauer stage which is a specialized non-feeding larval stage. In the dauer stage, worms display astonishingly low metabolism, which allows them to adapt themselves to environmental stress and to dwell without food for several months. Dauer larvae can enter into the reproductive larval stage, when environmental conditions become favorable. In this study, the metabolic transition of dauers into the reproductive larval stage is analyzed in detail:
a. During the exit of dauers, several metabolic traits were examined. Primarily, dauer larva initiates the metabolic transition by activating feeding, which is followed by upregulated oxygen consumption and mitochondrial remodeling, as well as enhanced protein synthesis.
b. To better understand the metabolic transition, inhibitors of the dauer exit were introduced. Lithium ions were shown to inhibit the transition of dauers to reproductive larvae and prevent the upregulation of metabolic activities required for this process.
c. In liquid culture, the transition from the dauer to the reproductive larva is also inhibited, presumably because of the hypoxic character of the liquid culture. Thus, hypoxia has a negative effect on the metabolic transition.
d. In the course of our investigation we discovered that the dauer larva is not a closed system but indeed, it can dwell on the externally available ethanol as a carbon source by incorporating it into the energy metabolism. This allows dauers to survive for longer periods in the absence of bacteria, the preferred food of worms.
These findings clarify the nature of dauers, how they utilize distinct pathways during the metabolic transition and how they take advantage of the externally available carbon source. These results may in the future enable us to elucidate the complex pathways of metabolism, as well as the ways in which it can be regulated.
2
Ailion, Michael Edward. "Dauer formation at high temperatures in Caenorhabditis elegans /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/5070.
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Schackwitz, Wendy. "Genetic and neural processing of the dauer pheromone response in Caenorhabditis elegans /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10280.
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Estevez, Annette Orene Zager. "The role of the daf-8 gene in Caenorhabditis elegans dauer larva development /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9841284.
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Ludewig, Hanno Andreas. "Nuclear receptor pathways in Caenorhabditis elegans: DIN-1, a DAF-12 coregulator of dauer diapause and developmental arrest." [S.l.] : [s.n.], 2003. http://www.diss.fu-berlin.de/2003/265/index.html.
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Jensen, Victor L. "Novel components of the dauer larva developmental signaling pathway in Caenorhabditis elegans." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/30446.
Full textAbstract:
In harsh conditions Caenorhabditis elegans arrests development to enter a nonaging,
resistant diapause state called the dauer larva. Olfactory sensation modulates the
TGF-β and insulin-like signaling pathways to control this developmental decision. The
dauer pheromone is required for formation of dauer larvae. This thesis shows that
bacterial pathogenesis is an input into dauer formation in addition to the known inputs of
starvation, overcrowding and high temperature. This was first suggested by the overabundance
of innate immunity genes found in a screen for novel synthetic dauer
formation mutants. A total of 21 genes were identified in this screen, only one of which,
srh-100, was previously identified to influence dauer formation. This work also
characterizes new genes and functions that define early, middle, and late steps in the
dauer pathway. Epistasis analysis and a GFP-tagged reporter places DAF-25 (abnormal
DAuer Formation) function in the sensory cilia. DAF-25 was shown to be required for
DAF-11 cilia localization as well as proper olfaction to various cues. daf-25 and daf-11
mutants have similar phenotypes and epistatic order. Intraflagellar transport is not
defective in daf-25 mutants although the ciliary localization of DAF-25 itself is altered in
a mutant that is defective in retrograde IFT. A Daf-c enhancing mutant originally isolated
as a double mutant with a novel daf-2 allele was also identified. m708 is allelic with sdf-9
(Synthetic Dauer Formation). Epistasis analysis and allele-specific interactions place it in
the daf-2 pathway as a possible DAF-2 interactor. The molecular lesion in m708 was
identified to be an insertion of the mariner transposon Cemar1. This is the first identified
hopping event described for this transposon family, the largest in C. elegans. Finally, zip-
5 (initially identified as a candidate DAF-16/FOXO target by serial analysis of gene
expression) was shown to be a basic-leucine zipper transcription factor (bZIP) that is
down regulated in a daf-2 background. zip-5 mutants show an extension of life span that
is dependent on SKN-1, a bZIP-like transcription factor. ZIP-5 expression is dependant
on the longevity-associated DAF-16 transcription factor and the zip-5 GATA binding
sites.
7
Xie, Meng. "AMPK-dependent regulation of lipid metabolism in the C. elegans dauer larva." Thesis, McGill University, 2014. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=123178.
Full textAbstract:
Caenorhabditis elegans can enter an alternative dormant state called "dauer" to circumvent harsh environmental conditions. During this stage they cease their reproductive developmental program and food intake, while remaining fully viable and motile. During this stage increased levels of AMP-activated kinase (AMPK) blocks the exhaustion of the cellular energy depot by directly inhibiting a critical triglyceride lipase called ATGL-1. By performing a whole genome RNAi survey for genes that, when compromised, enhance the survival of AMPK mutant dauers I revealed that catalase genes were somehow involved in dauer survival in the mutants. I showed that increased hydrogen peroxide, to an optimal level, can alter both the abundance and the nature of the fatty acid content through HIF-1 transcription factor-dependent expression of several fatty acid biosynthetic enzymes. In addition, I showed that the AMPK-dependent phosphorylation of ATGL-1 not only signals its polyubiquitylation and subsequent proteasome-dependent degradation, but also generates a 14-3-3 binding site, which is recognized by PAR-5, the C. elegans 14-3-3 protein homologue. This association sequesters ATGL-1 away from cellular lipid droplets thereby reducing its accessibility to substrate. By studying the C. elegans CGI-58 protein, I provide evidence that in addition to its previously characterised role as a co-activator of ATGL in mammals, it also functions to maintain lipid droplet structure and prevents lipid exchange and fusion events among the lipid droplets. In summary, my work characterizes several regulators of the lipolysis pathway that can shed light on development of novel therapeutic treatments for diseases associated with abnormal lipid storage, hydrolysis or general homeostasis.<br>Les Caenorhabditis elegans ont la capacité d'entrer dans une phase de dormance alternative appelée 'dauer', afin d'échapper à des conditions environnementales difficiles, pendant laquelle ils cessent de se développer et de se nourrir, tout en restant mobile, et accroissent leur capacité de résistance au stress, si bien qu'ils sont capables de vivre quatre fois plus longtemps que les animaux adultes normaux. Les animaux dont la signalisation des insuline est en danger entrent dans une phase 'dauer' à une température restrictive, où la proteine AMPK agit comme un interrupteur qui limite la délivrance du dépôt d'énergie en ralentissant directement l'ATGL, l'enzyme restraignant le taux de tout le processus de lipolyse. En uitlisant des RNA interférants pour realiser une étude du génome, à la recherche de gènes, qui, lorsqu'ils sont compromis, améliorent la survie des AMPK mutantes dormantes, je révèle que le péroxyde d'hydrogène, lorsqu'il est augmenté à un niveau optimal, peut modifier à la fois l'abondance et la nature de la teneur en acide gras, à travers l'expression de facteur de transcription HIF-1 dépendant de plusieurs enzymes clés impliquées dans la biosynthèse des acides gras. De plus, je démontre que la phosphorylation catalysée par l'AMPK de l'ATGL-1 signale non seulement sa poly-ubiquitination, suivie de sa dégradation liée aux protéasomes, mais génère également un site de liaison 14-3-3. Ce dernier est reconnu par PAR-5, la protéine homologue de 14-3-3 des C. elegans, qui éloigne l'ATGL-1 des goutelettes lipidiques cellulaires, et donc décroit sa possibilité de former un substrat. En étudiant la protéine CGI-58 des C. elegans, j'apporte la preuve qu'en plus de son rôle de co-activateur de la protéine ATGL, observé chez les mammifères, elle agit également pour maintenir une structure de gouttelettes lipidiques normale et empêcher tout échange de lipides et toute fusion entre les gouttelettes lipidiques. En résumé, mon travail met en lumière plusieurs régulateurs de l'action de lypolyse qui peuvent avoir des conséquences sur le développement de traitements thérapeutiques novateurs pour les maladies associées aux lipides.
8
Abu, Sharkh Sawsan E. "Spectroscopic & thermodynamic investigations of the physical basis of anhydrobiosis in caenorhabditis elegans dauer larvae." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-164661.
Full textAbstract:
Anhydrobiotic organisms have the remarkable ability to lose extensive amounts of body water and survive in an ametabolic, suspended animation state. Distributed to various taxa of life, these organisms have evolved strategies to efficiently protect their cell membranes and proteins against extreme water loss. At the molecular level, a variety of mutually non-exclusive mechanisms have been proposed to account particularly for preserving the integrity of the cell membranes in the desiccated state. Recently, it has been shown that the dauer larva of the nematode Caenorhabditis elegans is anhydrobiotic and accumulates high amounts of trehalose during preparation for harsh desiccation (preconditioning), thereby allowing for a reversible desiccation / rehydration cycle.
Here, we have used this genetic model to study the biophysical manifestations of anhydrobiosis and show that, in addition to trehalose accumulation, the dauer larvae exhibit a systemic chemical response upon preconditioning by dramatically reducing their phosphatidylcholine (PC) content. The C. elegans strain daf-2 was chosen for these studies, because it forms a constitutive dauer state under appropriate growth conditions. Using complementary approaches such as chemical analysis, time-resolved FTIR-spectroscopy, Langmuir-Blodgett monolayers, and fluorescence spectroscopy, it is shown that this chemical adaptation of the phospholipid (PL) composition has key consequences for their interaction with trehalose. Infrared-spectroscopic experiments were designed and automated to particularly address structural changes during fast hydration transients.
Importantly, the coupling of headgroup hydration to acyl chain order at low humidity was found to be altered on the environmentally relevant time scale of seconds. PLs from preconditioned larvae with reduced PC content exhibit a higher trehalose affinity, a stronger hydration-induced gain in acyl chain free volume, and a wider spread of structural relaxation rates during lyotropic transitions and sub- headgroup H-bond interactions as compared to PLs from non-preconditioned larvae. The effects are related to the intrinsically different hydration properties of PC and phosphatidylethanolamine (PE) headgroups, and lead to a larger hydration-dependent rearrangement of trehalose-mediated H-bond network in PLs from preconditioned larvae. This results in a lipid compressibility modulus of ∼0.5 mN/m and 1.2 mN/m for PLs derived from preconditioned and non-preconditioned larvae, respectively.
The ensemble of these changes evidences a genetically controlled chemical tuning of the native lipid composition of a true anhydrobiote to functionally interact with a ubiquitous protective disaccharide. The biological relevance of this adaptation is the preservation of plasma membrane integrity by relieving mechanical strain from desiccated trehalose- containing cells during fast rehydration. Finally, the thermo-tropic lipid phase behavior was studied by temperature-dependent ATR-FTIR and fluorescence spectroscopy of LAURDAN-labeled PLs. The results show that the adaptation to drought, which is accomplished to a significant part by the reduction of the PC content, relies on reducing thermo-tropic and enhancing lyotropic phase transitions. The data are interpreted on a molecular level emphasizing the influence of trehalose on the lipid phase transition under biologically relevant conditions by a detailed analysis of the lipid C=O H-bond environment.
The salient feature of the deduced model is a dynamic interaction of trehalose at the PL headgroup region. It is proposed here that the location of trehalose is changed from a more peripheral to a more sub-headgroup-associated position. This appears to be particularly pronounced in PLs from preconditioned worms. The sugar slides deeper into the inter-headgroup space during hydration and thereby supports a quick lateral expansion such that membranes can more readily adapt to the volume changes in the swelling biological material at reduced humidity. The data show that the nature of the headgroup is crucial for its interaction with trehalose and there is no general mechanism by which the sugar affects lipidic phase transitions. The intercalation into a phosphatidylethanolamine-rich membrane appears to be unique.
In this case, neither the phase transition temperature nor its width is affected by the protective sugar, whereas strong effects on these parameters were observed with other model lipids. With respect to membrane preservation, desiccation tolerance may be largely dependent on reducing phosphatidylcholine and increasing the phsophatidylethanolamine content in order to optimize trehalose headgroup interactions. As a consequence, fast mechanical adaptation of cell membranes to hydration-induced strain can be realized.
9
Kaptan, Damla [Verfasser], Teymuras [Akademischer Betreuer] Kurzchalia, Christian [Gutachter] Dahmann, and Bart [Gutachter] Braeckmann. "Metabolic Transition in Caenorhabditis elegans Dauer Larva / Damla Kaptan ; Gutachter: Christian Dahmann, Bart Braeckmann ; Betreuer: Teymuras Kurzchalia." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1130092895/34.
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Shorto, Alison. "Life history consequences of phenotypic plasticity of dauer larva formation in the free-living nematode Caenorhabditis elegans." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443220.
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Kaptan, Damla [Verfasser], Teymuras Akademischer Betreuer] Kurzchalia, Christian [Gutachter] [Dahmann, and Bart [Gutachter] Braeckmann. "Metabolic Transition in Caenorhabditis elegans Dauer Larva / Damla Kaptan ; Gutachter: Christian Dahmann, Bart Braeckmann ; Betreuer: Teymuras Kurzchalia." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-223034.
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Gaglia, Marta Maria. "Dopamine modulation of quiescence in dauer larvae, and other investigations on hibernation and lifespan in the nematode Caenorhabditis elegans." Diss., Search in ProQuest Dissertations & Theses. UC Only, 2008. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3339187.
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13
Friberg, Josefin. "The control of growth and metabolism in Caenorhabditis elegans." Doctoral thesis, Umeå : Umeå Centre for Molecular Pathogenesis, Umeå University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-710.
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Becker, Ben Verfasser], Adam [Akademischer Betreuer] Antebi, Thorsten [Akademischer Betreuer] Hoppe, and Mats [Akademischer Betreuer] [Paulsson. "Small Molecule Modulators of Dauer Formation and Longevity in Caenorhabditis Elegans / Ben Becker. Gutachter: Adam Antebi ; Thorsten Hoppe ; Mats Paulsson." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1055038655/34.
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Becker, Ben [Verfasser], Adam Akademischer Betreuer] Antebi, Thorsten [Akademischer Betreuer] Hoppe, and Mats [Akademischer Betreuer] [Paulsson. "Small Molecule Modulators of Dauer Formation and Longevity in Caenorhabditis Elegans / Ben Becker. Gutachter: Adam Antebi ; Thorsten Hoppe ; Mats Paulsson." Köln : Universitäts- und Stadtbibliothek Köln, 2014. http://d-nb.info/1055038655/34.
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Djeddi, Abderazak. "Caractérisation cellulaire et fonctionnelle de l’autophagie : interactions avec la voie de maturation endosomale chez Caenorhabditis elegans." Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112036.
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L’autophagie est une voie catabolique durant laquelle des constituants cytoplasmiques sont engloutis dans des vésicules à double membrane nommées autophagosomes. Elle sert à éliminer les protéines mal repliées ou les agrégats protéiques, à détruire les organites défectueux comme les mitochondries, le réticulum endoplasmique et les peroxysomes mais aussi des pathogènes intracellulaires. Le matériel séquestré dans les autophagosomes est ensuite envoyé, pour dégradation, vers le lysosome. La dégradation du matériel séquestré génère des nucléotides, des acides aminés et des acides gras qui seront recyclés en vue de la synthèse de macromolécules et de la génération d’ATP.Dans cette étude nous explorons l’aspect cellulaire et fonctionnel de la voie de l’autophagie chez Caenorhabditis elegans. Nous montrons que le génome du nématode contient deux homologues du gène autophagique de levure Atg8. Ces homologues codent pour les protéines LGG-1 et LGG-2 qui sont des protéines des membranes des autophagosomes. Ces protéines agissent de façon synergique dans les processus physiologiques impliquant l’autophagie, en l’occurrence, la longévité et la formation des larves dauer.Nous montrons également que l’autophagie est impliquée dans le maintien de l’homéostasie cellulaire chez les mutants ESCRT. Les complexes ESCRT sont impliqués dans l’adressage des protéines ubiquitinées vers les corps multi vésiculaires pour les dégrader. Les mutants ESCRT se caractérisent par des altérations cellulaires et développementales. Nos résultats indiquent que l’inactivation des ESCRT cause une augmentation du flux autophagique. L’inactivation de l’autophagie dans ces mutants exacerbe les défauts cellulaires alors que son induction protège de la dégradation<br>Macroautophgagy is a catabolic process involved in the clearance of cellular components in the lysosome when cells face starvation conditions. This eukaryotic process requires the formation of double membrane vesicles named autophagosomes. Autophagy is implicated in the elimination of misfolded proteins, protein aggregates and long-lived or damaged organelles such as mitochondria, endoplasmic reticulum and peroxysomes. It is alos required for the clearance of intracellular pathogens. The material enclosed inside autophagososmes in degraded in the lysosome: nucleotides, amino-acids and fatty-acids are generated and reused for neosynthesis of macromolecules and ATP.In the present study, we are exploring the cellular and functional aspects of the autophagic pathway in Caenorhabditis elegans. We show that the genome of the worm contain two homologues of the Yeast autophagic gene, Atg8. These homlogues encode for two proteins namely, LGG-1 and LGG-2, which localize to the autophagosomal membranes. We have shown that this two proteins act synergistically in dauer formation and longevity.We have also shown that autophagy play an important role in maintaining cell homeostasis in endosomal maturation mutans. These latter mutants show defects in the ESCRT coplexes (Endosomal Sorting Complex Required for Transport). ESCRT complexes are required the recycling of cell surface receptors and for the sorting of ubiquitinated prtoteins into the multivesicular bodies. Mutations in the ESCRTs cause cellular et developmental defects. In our study, we show that autophagy is induced in these mutants and play a beneficial role in correcting cellular defects
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Saini, Ratni, Sebastian Boland, Olga Kataeva, Arndt W. Schmidt, Teymuras V. Kurzchalia, and Hans-Joachim Knölker. "Stereoselective synthesis and hormonal activity of novel dafachronic acids and naturally occurring steroids isolated from corals." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-139217.
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A stereoselective synthesis of (25S)-Δ1-, (25S)-Δ1,4-, (25S)-Δ1,7-, (25S)-Δ8(14)-, (25S)-Δ4,6,8(14)-dafachronic acid, methyl (25S)-Δ1,4-dafachronate and (25S)-5α-hydroxy-3,6-dioxocholest-7-en-26-oic acid is described. (25S)-Δ1,4-Dafachronic acid and its methyl ester are natural products isolated from corals and have been obtained by synthesis for the first time. (25S)-5α-Hydroxy-3,6-dioxocholest-7-en-26-oic acid represents a promising synthetic precursor for cytotoxic marine steroids<br>Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
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Abu, Sharkh Sawsan E. [Verfasser], Karim [Akademischer Betreuer] Fahmy, Stefan [Akademischer Betreuer] Diez, and Andreas [Akademischer Betreuer] Barth. "Spectroscopic & thermodynamic investigations of the physical basis of anhydrobiosis in caenorhabditis elegans dauer larvae / Sawsan E. Abu Sharkh. Gutachter: Stefan Diez ; Andreas Barth. Betreuer: Karim Fahmy." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://d-nb.info/1070478172/34.
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Saini, Ratni, Sebastian Boland, Olga Kataeva, Arndt W. Schmidt, Teymuras V. Kurzchalia, and Hans-Joachim Knölker. "Stereoselective synthesis and hormonal activity of novel dafachronic acids and naturally occurring steroids isolated from corals." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27813.
Full textAbstract:
A stereoselective synthesis of (25S)-Δ1-, (25S)-Δ1,4-, (25S)-Δ1,7-, (25S)-Δ8(14)-, (25S)-Δ4,6,8(14)-dafachronic acid, methyl (25S)-Δ1,4-dafachronate and (25S)-5α-hydroxy-3,6-dioxocholest-7-en-26-oic acid is described. (25S)-Δ1,4-Dafachronic acid and its methyl ester are natural products isolated from corals and have been obtained by synthesis for the first time. (25S)-5α-Hydroxy-3,6-dioxocholest-7-en-26-oic acid represents a promising synthetic precursor for cytotoxic marine steroids.<br>Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
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Armstrong, Kristin R. "Multiple Mechanisms Contribute to Regulation of Gene Expression in the C. elegans Excretory System." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1214071705.
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Colella, Eileen. "Investigating the genetic basis of germline quiescence in «C. elegans» dauers." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32534.
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When faced with unsatisfactory environmental conditions, young C. elegans larvae can enter a diapause-like stage called dauer. The decision to form dauer is controlled by three parallel signalling pathways (TGF-β, cGMP and insulin/IGF-like signalling) that converge on DAF-12, a nuclear hormone receptor that prompts either dauer formation or reproductive growth depending on the environmental cues presented to C. elegans during its development. DAF-12 is related to the Vitamin D, Liver-X, and Androstane receptors, and similar to these human NHRs, responds to cholesterol-derived hormones. Ligand-bound DAF-12 has transcriptional activity directing reproductive development, while unliganded DAF-12 forms a dauer-specifying complex that regulates the transcription of genes required for dauer development with its interacting protein DIN-1S. I report here that din-1S is required in the germ cells upstream of insulin-like signalling (IlS) and in parallel to LKB1/par-4 signalling to establish dauer germline quiescence. I also observed that din-1S is important for post-dauer reproductive fitness when IlS is impaired. Moreover, I demonstrate that din-1S is necessary for long dauer life span in response to reduced insulin signalling, either downstream of, or in parallel to, AMPK/aak-2. Finally, I show that din-1S acts upstream of IlS pathway components to restrict somatic gonad precursor cell proliferation during dauer development, and uncover a conditional role for LKB1/par-4 signalling in this process.<br>Chez C. elegans, des conditions de croissance inadéquates promeuvent l'entrée dans un stade de dormance appelé dauer. La décision d'entrer en dauer est contrôlée par trois cascades de signalisation parallèles qui convergent sur DAF-12, un récepteur d'hormone nucléaire qui, dépendamment des signaux environnementaux qui se présentent à l'animal pendant son développement, l'incite à entrer en dauer ou à croître reproductivement. DAF-12 est apparenté aux récepteurs de la Vitamine D, des oxystérols et des androstanes et, comme ces récepteurs nucléaires humains, réagit à des hormones dérivées du cholestérol. En présence de son ligand, DAF-12 possède une activité transcriptionnelle qui dirige le développement reproductif, tandis qu'en l'absence de cette hormone, DAF-12 forme un complexe spécifique au stade dauer avec son partenaire DIN-1S et régule la transcription de gènes requis pour le développement de ce stade. Mes analyses génétiques suggèrent que din-1S est requis dans la lignée germinale en amont de la cascade de signalisation par l'insuline et en parallèle de LKB1/par-4, afin d'établir la dormance des cellules germinales pendant le développement du stade dauer. Je démontre que din-1S est nécessaire pour le succès reproductif après ce stade lorsque la cascade de signalisation par l'insuline est perturbée. Je révèle aussi que din-1S est essentiel pour la longue vie des larves dauer en réponse à une réduction de signalisation par l'insuline, en aval ou bien en parallèle de AMPK/aak-2. Finalement, je montre que din-1S fonctionne en aval des composantes de la voie de signalisation par l'insuline afin d'empêcher la prolif
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Kaptan, Damla. "Metabolic Transition in Caenorhabditis elegans Dauer Larva." Doctoral thesis, 2016. https://tud.qucosa.de/id/qucosa%3A30266.
Full textAbstract:
Under unfavorable environmental conditions Caenorhabditis elegans larvae enter a dauer stage which is a specialized non-feeding larval stage. In the dauer stage, worms display astonishingly low metabolism, which allows them to adapt themselves to environmental stress and to dwell without food for several months. Dauer larvae can enter into the reproductive larval stage, when environmental conditions become favorable. In this study, the metabolic transition of dauers into the reproductive larval stage is analyzed in detail:
a. During the exit of dauers, several metabolic traits were examined. Primarily, dauer larva initiates the metabolic transition by activating feeding, which is followed by upregulated oxygen consumption and mitochondrial remodeling, as well as enhanced protein synthesis.
b. To better understand the metabolic transition, inhibitors of the dauer exit were introduced. Lithium ions were shown to inhibit the transition of dauers to reproductive larvae and prevent the upregulation of metabolic activities required for this process.
c. In liquid culture, the transition from the dauer to the reproductive larva is also inhibited, presumably because of the hypoxic character of the liquid culture. Thus, hypoxia has a negative effect on the metabolic transition.
d. In the course of our investigation we discovered that the dauer larva is not a closed system but indeed, it can dwell on the externally available ethanol as a carbon source by incorporating it into the energy metabolism. This allows dauers to survive for longer periods in the absence of bacteria, the preferred food of worms.
These findings clarify the nature of dauers, how they utilize distinct pathways during the metabolic transition and how they take advantage of the externally available carbon source. These results may in the future enable us to elucidate the complex pathways of metabolism, as well as the ways in which it can be regulated.
23
Abu, Sharkh Sawsan E. "Spectroscopic & thermodynamic investigations of the physical basis of anhydrobiosis in caenorhabditis elegans dauer larvae." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A28646.
Full textAbstract:
Anhydrobiotic organisms have the remarkable ability to lose extensive amounts of body water and survive in an ametabolic, suspended animation state. Distributed to various taxa of life, these organisms have evolved strategies to efficiently protect their cell membranes and proteins against extreme water loss. At the molecular level, a variety of mutually non-exclusive mechanisms have been proposed to account particularly for preserving the integrity of the cell membranes in the desiccated state. Recently, it has been shown that the dauer larva of the nematode Caenorhabditis elegans is anhydrobiotic and accumulates high amounts of trehalose during preparation for harsh desiccation (preconditioning), thereby allowing for a reversible desiccation / rehydration cycle.
Here, we have used this genetic model to study the biophysical manifestations of anhydrobiosis and show that, in addition to trehalose accumulation, the dauer larvae exhibit a systemic chemical response upon preconditioning by dramatically reducing their phosphatidylcholine (PC) content. The C. elegans strain daf-2 was chosen for these studies, because it forms a constitutive dauer state under appropriate growth conditions. Using complementary approaches such as chemical analysis, time-resolved FTIR-spectroscopy, Langmuir-Blodgett monolayers, and fluorescence spectroscopy, it is shown that this chemical adaptation of the phospholipid (PL) composition has key consequences for their interaction with trehalose. Infrared-spectroscopic experiments were designed and automated to particularly address structural changes during fast hydration transients.
Importantly, the coupling of headgroup hydration to acyl chain order at low humidity was found to be altered on the environmentally relevant time scale of seconds. PLs from preconditioned larvae with reduced PC content exhibit a higher trehalose affinity, a stronger hydration-induced gain in acyl chain free volume, and a wider spread of structural relaxation rates during lyotropic transitions and sub- headgroup H-bond interactions as compared to PLs from non-preconditioned larvae. The effects are related to the intrinsically different hydration properties of PC and phosphatidylethanolamine (PE) headgroups, and lead to a larger hydration-dependent rearrangement of trehalose-mediated H-bond network in PLs from preconditioned larvae. This results in a lipid compressibility modulus of ∼0.5 mN/m and 1.2 mN/m for PLs derived from preconditioned and non-preconditioned larvae, respectively.
The ensemble of these changes evidences a genetically controlled chemical tuning of the native lipid composition of a true anhydrobiote to functionally interact with a ubiquitous protective disaccharide. The biological relevance of this adaptation is the preservation of plasma membrane integrity by relieving mechanical strain from desiccated trehalose- containing cells during fast rehydration. Finally, the thermo-tropic lipid phase behavior was studied by temperature-dependent ATR-FTIR and fluorescence spectroscopy of LAURDAN-labeled PLs. The results show that the adaptation to drought, which is accomplished to a significant part by the reduction of the PC content, relies on reducing thermo-tropic and enhancing lyotropic phase transitions. The data are interpreted on a molecular level emphasizing the influence of trehalose on the lipid phase transition under biologically relevant conditions by a detailed analysis of the lipid C=O H-bond environment.
The salient feature of the deduced model is a dynamic interaction of trehalose at the PL headgroup region. It is proposed here that the location of trehalose is changed from a more peripheral to a more sub-headgroup-associated position. This appears to be particularly pronounced in PLs from preconditioned worms. The sugar slides deeper into the inter-headgroup space during hydration and thereby supports a quick lateral expansion such that membranes can more readily adapt to the volume changes in the swelling biological material at reduced humidity. The data show that the nature of the headgroup is crucial for its interaction with trehalose and there is no general mechanism by which the sugar affects lipidic phase transitions. The intercalation into a phosphatidylethanolamine-rich membrane appears to be unique.
In this case, neither the phase transition temperature nor its width is affected by the protective sugar, whereas strong effects on these parameters were observed with other model lipids. With respect to membrane preservation, desiccation tolerance may be largely dependent on reducing phosphatidylcholine and increasing the phsophatidylethanolamine content in order to optimize trehalose headgroup interactions. As a consequence, fast mechanical adaptation of cell membranes to hydration-induced strain can be realized.
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Tenen, Claudia. "Function and tissue focus of daf-18/PTEN in maintaining blast cell multipotency and quiescence in Caenorhabditis elegans dauer larvae." Thesis, 2019. https://doi.org/10.7916/d8-3hts-7m21.
Full textAbstract:
Cellular quiescence, a reversible state of cell-cycle exit, and developmental potential, the ability to differentiate into appropriate cell types, are properties essential for normal development and stem cell function (reviewed in (Cheung and Rando, 2013; Fiore et al., 2018; Mihaylova et al., 2014). Understanding the mechanisms by which cells maintain quiescence has important implications for developmental biology, as this reversible state of cell-cycle exit is a key attribute of stem cells, as well as for cancer biology, as quiescence plays a key role in tumor dormancy and metastasis. Environmental conditions are key in regulating whether stem cells maintain quiescence or exit to resume divisions and developmentally progress. I aim to investigate how the properties of quiescence and developmental potential are retained over long periods of time and how they are appropriately regulated by external environmental inputs. The nematode Caenorhabditis elegans is an excellent model for investigating both of these questions because it is capable of entering and maintaining a developmentally arrested state for an unusually long time compared to the normal lifetime of the worm, and because the decision to enter this arrest is regulated entirely by external environmental inputs (Cassada and Russell, 1975).
Upon encountering conditions unfavorable for growth, C. elegans enters an alternative, developmentally arrested state called dauer diapause in which precursor cells remain quiescent for months – a period many times the lifespan of a worm grown under favorable conditions (Cassada and Russell, 1975). Maintaining precursors in this arrested state is important in order for the worms to develop normally once conditions improve and requires components of the conserved Insulin/Insulin-like (IIS) signaling pathway (Karp and Greenwald 2013 and this work); of note, the IIS pathway also regulates mammalian quiescence (Eijkelenboom and Burgering, 2013). Canonical regulation of dauer diapause includes IIS, TGFß, and dafachronic acid (DA)/nuclear hormone receptor (NHR) signaling (reviewed in (Murphy and Hu, 2013a)).
Here, I investigate how DAF-18, the sole C. elegans ortholog of the tumor suppressor PTEN (Phosphatase and tensin homolog) (Gil et al., 1999; Mihaylova et al., 1999; Ogg and Ruvkun, 1998; Rouault et al., 1999), maintains quiescence in dauer through regulation of these conserved signaling pathways using the C. elegans gonad as a model. The gonad is composed of somatic cells and the germline. Both the somatic gonad and germline develop post-embryonically from precursor cells present when dauer arrest occurs, and these precursor cells remain quiescent for the duration of dauer diapause (Cassada and Russell, 1975; Hong et al., 1998; Narbonne and Roy, 2006). After exit from dauer, division and differentiation resume. DAF-18/PTEN is required for germline quiescence during dauer diapause (Narbonne and Roy, 2006), and my results implicate DAF-18/PTEN in the control of quiescence of the somatic tissues as well, including the somatic gonad. In this role, DAF-18/PTEN activity in the somatic gonad non-autonomously coordinates both germline stem cell (GSC) and somatic gonad blast (SGB) quiescence. I have demonstrated this somatic gonad focus through mosaic analysis, tissue-specific rescue, and tissue-specific excision mosaics. We propose that DAF-18/PTEN mediates production of a signal promoting quiescence from the somatic gonad to the SGBs and GSCs and that this signal does not absolutely require or solely target the IIS, TGFß, or DA/NHR signaling pathways normally implicated in regulation of dauer diapause.
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Ludewig, Hanno Andreas [Verfasser]. "Nuclear receptor pathways in Caenorhabditis elegans: DIN-1, a DAF-12 coregulator of dauer diapause and developmental arrest / von Hanno Andreas Ludewig." 2003. http://d-nb.info/969165498/34.
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Fröde, Stephan. "Drei neu identifizierte Gene in der Morphogenese von Caenorhabditis elegans: pcp-2, pcp-3 und gon-12 sind sowohl während dem dritten Larvalstadium, als auch im alternativen Dauerlarvenstadium aktiv und regulieren die Entwicklung reproduktiver Organe." Doctoral thesis, 2003. http://hdl.handle.net/11858/00-1735-0000-000D-F181-1.
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