Dissertations / Theses on the topic 'Brittle stars'

Abstract Regeneration processes are very complex developmental phenomena, occurring in adult and larval organisms, which require not only new cell formation but also detailed information to specify the identity of tissues to be generated at the wound site. Regeneration after injury requires several changes in terms of activation of cellular mechanisms, activities and behavior and regenerating tissues initiate diverse processes such as wound healing, programmed cell death, dedifferentiation/transdifferentiation, stem (or progenitor) cell proliferation, differentiation. Regeneration, in which lost or damage tissue are re-grown, requires specification of the identity of new tissues to be made at specific positions. In general, it is not yet understood whether this process relies only on intrinsic regulative properties of regenerating tissues or whether positional information provides input into tissue re-patterning. However, there are still few established experimental systems that enable the study of this issue in regenerating animals, especially considering animals closely related to vertebrates, the echinoderms, which are a deuterostomian, group phylogenetically related to chordates. Larval and adult echinoderms from each of the five classes present a natural and rapid regeneration potential. Among echinoderms, ophiuroids (or brittlestars) are well known for possessing a remarkable regeneration plasticity, in many species expressed by the ability to rapidly and completely regenerate arms lost following self-induced (autotomy) or traumatic amputation. In spite of the well documented regenerative phenomena, there is still a huge lack of studies providing large-scale identification of genes involved in the molecular architecture of ophiuroid wonderful regeneration capabilities. Therefore, this thesis focuses on the study of cellular and molecular aspects of arm regeneration in ophiuroid models. As far as the cellular aspects are concerned different approaches were followed. The first one followed the overall arm regeneration process in Ophioderma longicauda model. Microscopic analysis allowed the characterization and reconstruction of the main phases in its morphogenetic and histogenetic events from self-induced amputation event up to 12 weeks regrowth. This results confirmed that arm regeneration in ophiuroids is achieved through a combination of morphallactic and epimorphic processes involved both in recycling and reorganization of old tissues and blastema formation. In addition, a rough comparison with the regeneration phenomena in other close species, Ophioderma appressa and Ophioderma cinerea, was provided in order to confirm the general aspects of the process. The second approach was focussed on another model species, Amphiura filiformis, whose arm regeneration process has been previously studied in detail. Hence, the selected experimental model was the explant, i.e. an isolated arm fragment obtained by a double amputation of the arm, proximal and distal maintained in living conditions up to 39 days. Here the morphogenetic and histogenetic events leading to the regrowth of a regenerating arm from the distal explant end were reconstructed in order to complement the previous results of the normal arm. The explant regeneration following double amputation in A. filiformis demonstrated a clear developmental polarity expressed by regeneration of the arm on the distal end and by cicatrization on the proximal end. As far as the molecular aspects, the work was addressed by trying to identify misregulated genes during early regenerative processes in arm regeneration of O. longicauda. An SSH library resulted in the identification of a fragment of the cDNA encoding the DNAJ, subfamily C member 7-like (DNAJC7) protein from regenerating arms (24 and 48 hours). This 341 bp cDNA clone matches to the 3`UTR region of a Strongylocentrotus purpuratus DNAJ ortholog (79% identity), a member of the DNAJ heat shock proteins (HSP 40) family. The optimized set up of in-situ hybridization (ISH) on the whole animal arm showed a clear expression in the radial water canal system (RWC) of both the freshly cut and the regenerating arm at 24 h and 48 h. A quantitative qRT-PCR disclosed a marked up regulation of this gene during regeneration. Based on the above-mentioned evidences we hypothesized a potential involvement of DNAJC7 like in arm regeneration in the ophiuroid O. longicauda. Keywords: Echinoderms, ophiuroids, arm regeneration, explants, molecular aspects, misregulated genes, DNAJ

The South African Ophiuroidea were last reviewed by Clark and Courtman-Stock in 1976. In the current investigation, the systematics of the group is thus revised in its entirety for the first time in 40 years. The data used originated from a number of sources. Existing data were sourced from i) published literature, ii) large expeditions or survey data, iii) South African institutional collections and iv) international museums. The majority of new records and data were sourced from previously unidentified specimens deposited in the collections of various South African and international museums and/or institutions, as well as from photographic records and some new, project-specific collecting. A review is presented of the history of ophiuroid taxonomy in South Africa highlighting the progression of research and of species discovery in the region since 1783. All new records of Ophiuroidea from South Africa since (and including) 1977 are documented, with each species account detailing key references, distribution, ecology and additional remarks. As a result, an additional 28 species are added to the known fauna of the mainland Exclusive Economic Zone of continental South Africa, raising the total known number of ophiuroid species in the region to 136. The genus Ophiocoma Agassiz (Echinodermata: Ophiuroidea: Ophiurida: Ophiocomidae) is reviewed and the number of species in South Africa increased from four to eight. All species are briefly discussed in terms of taxonomy, geographic distribution and ecology. Furthermore, the juveniles of O. brevipes, which were found on the ventral side of some adult Ophiocoma brevipes specimens, are described in detail. The distribution of the type material of O. scolopendrina has led to some confusion, and it is considered appropriate to establish a neotype from the original type locality (Mauritius).

Gorgonocephalus eucnemis, Ophiothrix suensonii and Ophiothrix spiculata are aerobic Echinoderms. Previous observations on the anatomy of these two genera state five pairs of radial shields and genital plates are responsible for regulating the position of the roof of the body disc and the flushing of water in and out of the bursae. Rates of bursal ventilation increase by an average 60-64% when the ophiuroid is exposed to an increase in food or a decrease in dissolved oxygen in Gorgonocephalus. When exposed to hypoxic oxygen concentrations O. suensonii and O. spiculata increased bursal-ventilation rates by (means of) 35% and 28%. Measurements of DO from inside and outside the bursae show that DO is being absorbed during bursal-ventilations. These findings suggest bursal ventilation is a means of respiration and increased rates of bursal-ventilation may help meet increased oxygen demands during feeding and some periods of hypoxia. This dissertation includes unpublished, co-authored material.

<p> The formation of mineralized tissue was critical to the evolution and diversification of metazoans and remains functionally significant in most animal lineages. Of special importance is the protein found occluded within the mineral matrix, which facilitates the process of biomineralization and modulates the final mineral structure. These skeletal matrix proteins have well been described in several species, including the sea urchin <i> Stronglyocentrotus purpuratus,</i> an important model organism. Biomineralization research is limited in other echinoderm classes. This research encompasses the first description of mineral matrix proteins in a member of the echinoderm class Ophiuroidea. This work describes the skeletal matrix proteins of the brittle star <i>Ophiocoma wendtii</i> using bioinformatic and proteomic techniques. General characteristics of matrix protein are described and a number of candidate biomineralization related genes have been identified, cloned, and sequenced. The unique evolutionary and biochemical properties of brittle star skeletal matrix proteins are also described.</p>

Includes bibliographical references.<br>The brooding behaviour and brooded young are described for Ophioderma wahlbergii Müller & Troschel 1842, a large, common brittle star from the coastal waters of South Africa. Twenty specimens were collected each month from June 2013 – May 2014 (n = 240). The species was found to be gonochoric.

The recent emergence of transcriptomic data available for echinoderms opened up the possibility of using this group of animals to study the molecular aspects underlying their extreme regenerative abilities. I use the brittle star Amphiura filiformis as a model to understand the cellular and molecular aspects of skeletogenesis during adult arm regeneration. This allowed me to begin compiling essential preparatory work for studying the gene regulatory network (GRN) underlying adult regeneration of the skeleton, which can be compared with the embryonic developmental program. I first studied the anatomy and morphogenesis of the skeleton during arm regeneration in A. filiformis, and defined a staging system relevant for the early developmental events occurring in the first 8 days post-amputation. I then established methods for spatio-temporal expression analysis and pharmacological treatments to characterise genes involved in adult arm regeneration in this brittle star. 18 genes expressed in embryonic skeletogenic cells (transcription factors, signalling receptors and downstream differentiation genes) were found to be expressed in the dermal layer of early stage regenerates, where skeletal spicules first form. This showed a very similar molecular signature of larval and regenerating arm skeletogenic cells. FGF signalling perturbation using the SU5402 inhibitor interfered with skeleton formation both in embryonic development and adult regeneration of the brittle star. A large-scale comparison revealed a conservation of a cohort of genes affected by SU5402 downstream of FGF signalling between those two developmental stages. In conclusion we found morphological and molecular similarities underlying skeletogenesis during regeneration and embryonic development suggesting that the gene regulatory network driving skeletogenic cell specification and differentiation could be re-activated in adult arm regeneration.

From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He IIλ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He II λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability.

The gastrula stage represents the point in development at which the three primary germ layers diverge. At this point the gene regulatory networks that specify the germ layers are established and the genes that define the differentiated states of the tissues have begun to be activated. These networks have been well characterized in sea urchins, but not in other echinoderms. Embryos of the brittle star Ophiocoma wendtii share a number of developmental features with sea urchin embryos, including the ingression of mesenchyme cells that give rise to an embryonic skeleton. Notable differences are that no micromeres are formed during cleavage divisions and no pigment cells are formed during development to the pluteus larva stage. More subtle changes in timing of developmental events also occur. To explore the molecular basis for the similarities and differences between these two echinoderms, the gastrula transcriptome of Ophiocoma wendtii was sequenced and characterized. I identified brittle star transcripts that correspond to 3385 genes in existing databases, including 1863 genes shared with the sea urchin Strongylocentrotus purpuratus gastrula transcriptome. I have characterized the functional classes of genes present in the transcriptome and compared them to those found in sea urchin. I then examined which members of the germ-layer specific gene regulatory networks (GRNs) of S. purpuratus are expressed in the O. wendtii gastrula. The results indicate that there is a shared "genetic toolkit" central to the echinoderm gastrula, a key stage in embryonic development, though there are also differences that reflect changes in developmental processes. The brittle star expresses genes representing all functional classes at the gastrula stage. Brittle stars and sea urchins have comparable numbers of each class of genes, and share many of the genes expressed at gastrula. Examination of the brittle star genes whose sea urchin orthologs are utilized in germ layer specification reveals a relatively higher level of conservation of key regulatory components compared to the overall transcriptome. I also identify genes that were either lost or whose temporal expression has diverged from that of sea urchins. Overall, the data suggest that embryonic skeleton formation in sea urchins and brittle stars represents convergent evolution by independent cooptation of a shared pathway utilized in adult skeleton formation. Transcription factors are of central importance to both development and evolution. Patterns of their expression and interactions form the gene regulatory networks which control the building of the embryonic body. Alterations in these patterns can result in the construction of altered bodies. To help increase understanding of this process, I compared the transcription factor mRNAs present in early gastrula-stage embryos of the brittle star Ophiocoma wendtii to those found in two species of sea urchins and a starfish. Brittle star homologs were found for one third of the transcription factors in the sea urchin genome and half of those that are expressed at equivalent developmental stages in sea urchins and starfish. Overall, the patterns of transcription factors found and not found in brittle star resemble those of other echinoderms, with the differences largely consistent with morphological differences. This study provides further evidence for the existence of deeply conserved developmental genetic processes, with various elements shared among echinoderms, deuterostomes, and metazoans.

Ophioderma longicauda (Bruzelius, 1805) est un complexe d’espèces cryptiques incluant six lignées mitochondriales (L1-L6), dont certaines (L2-L3-L4) incubent leur descendance, alors que d'autres se reproduisent probablement via des larves lécithotrophes. Afin de définir les limites d’espèces dans le complexe O. longicauda, le statut reproductif des lignées L1 et L3 a été étudié. L’analyse morphologique et génétique a montré qu’il s’agissait d’espèces biologiques différentes, avec notamment différentes périodes de reproduction. De plus, l’analyse par DAPC de 31 marqueurs génétiques a montré que le complexe O. longicauda était constitué de six groupes génétiques distincts. Deuxièmement, l’influence des traits d’histoire de vie sur la connectivité et la diversité génétique a été étudiée. Pour ce faire, 10 marqueurs ont été séquencés pour six populations sympatriques des lignées L1 et L3 en Grèce. La structure génétique était très marquée pour l’espèce incubante L3, tandis que l’espèce dispersante L1 n’a pas montré de structure génétique à cette échelle. L’analyse de la diversité génétique pour ces 10 marqueurs a montré que celle des dispersantes était trois à quatre fois plus élevée que celle des incubantes. De plus, l’analyse de la diversité génétique dans les transcriptomes des L1 et L3 a montré qu’elle était 1.5 à 2 fois plus élevée chez les dispersantes que chez les incubantes. Finalement, deux canaux ioniques impliqués dans la mobilité des spermatozoïdes ont montré une évolution sous sélection positive. Ces résultats suggèrent que la compétition des spermatozoïdes pourrait être un mécanisme d’isolement pré-zygotique chez Ophioderma longicauda<br>Ophioderma longicauda (Bruzelius, 1805) is a cryptic species complex including six mitochondrial lineages (L1-L6), of which three (L2-L3-L4) brood their juveniles, whereas the other lineages most likely reproduce using lecithotrophic larvae. In order to define the species limits in the O. longicauda complex, the reproductive status of lineages L1 and L3 was studied. The morphological and genetic study showed that they were different biological species, with notably different reproductive periods. In addition, the analysis of 31 genetic markers using DAPC showed that the O. longicauda complex included six distinct genetic groups. Secondly, the influence of life-history traits on connectivity and genetic diversity was studied. To do so, 10 markers were sequenced for six sympatric populations of lineages L1 and L3 from Greece. The genetic structure was high for the brooding species, whereas the broadcasting species did not display any genetic structure at that scale. The analysis of genetic diversity for these 10 markers showed that diversity was three to four times higher in broadcasters than in brooders. In addition, the analysis of genetic diversity in the L1 and L3 transcriptomes showed that diversity was 1.5 to 2 times higher in broadcasters than in brooders. Finally, two ion channels involved in sperm motility showed an evolution under positive selection. These results suggest that sperm competition might be a mechanism of pre-zygotic isolation in Ophioderma longicauda

碩士<br>國立中山大學<br>海洋生物研究所<br>87<br>Spawning induction by conspecifics were studied in two species of brittlestars Ophiocoma dentata (Muller and Troschel) and Ophiocoma scolopendrina (Lamarck) (Ophiuroidea: Ophicomidae) between June 1997 and July 1998 at Kenting, southern Taiwan. The reproductive periods of two species are both between April to June. In both species, ovary suspension can induce male spawning, but testis suspension cannot induce female spawning. There is no inductive effect between individuals of the same sex; and there is no effect between different species. There is spawning induction when the concentration of ovary suspension was 10-7 g/ml. The effective distance was 40 cm. The presumed inductive substance was found only in gonad tissues but not in arms and in disks. The one-way induction, i.e. females inducing males, may be an adaptation preventing sperm-dilution of these external fertilizing species in the sea.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.<br>Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6270. Adviser: Daniel B. Blake. Includes bibliographical references (leaves 571-610) Available on microfilm from Pro Quest Information and Learning.