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At least 343 records · Page 19Linked to original sources
PubMed2005

Regional specification in the early embryo of the brittle star Ophiopholis aculeata.

Early embryogenesis has been examined experimentally in several echinoderm and hemichordate classes. Although these studies suggest that the mechanisms which underlie regional specification have been highly conserved within the echinoderm + hemichordate clade, nothing is known about these mechanisms in several other echinoderm classes, including the Ophiuroidea. In this study, early embryogenesis was examined in a very little studied animal, the ophiuroid Ophiopholis aculeata. In O. aculeata, the first two cleavage planes do not coincide with the animal-vegetal axis but rather form approximately 45 degrees off this axis. A fate map of the early embryo was constructed using microinjected lineage tracers. Most significantly, this fate map indicates that there is a major segregation of ectodermal from endomesodermal fates at first cleavage. The distribution of developmental potential in the early embryo was also examined by isolating different regions of the early embryo and following these isolates though larval development. These analyses indicate that endomesodermal developmental potential segregates unequally at first, second, and third cleavage in O. aculeata. These results provide insight into the mechanisms of regional specification in O. aculeata and yield new material for the study of the evolution of echinoderm development.

Animals↗
PubMed2004

Complete mitochondrial genome DNA sequence for two ophiuroids and a holothuroid: the utility of protein gene sequence and gene maps in the analyses of deep deuterostome phylogeny.

The complete mitochondrial genome sequences have been determined for the holothuroid Cucumaria miniata and two ophiuroid species Ophiopholis aculeata and Ophiura lütkeni. In addition, the nucleotide sequence of the mitochondrial protein-coding genes for the asteroid Pisaster ochraceus has been completed. Maximum-likelihood and LogDet distance analyses of concatenated protein-coding sequences produced a series of trees that did not conclusively support generally accepted models of echinoderm phylogeny. The ophiuroid data consistently demonstrated accelerated nucleotide divergence rates and lack of stationarity. This confounds the phylogenetic analyses. Molecular investigations using individual protein-coding gene alignments demonstrated that the cytochrome b gene exhibits the least deviation in rate and stationarity and generated some trees consistent with proposed echinoderm phylogenies. Phylogenies based on echinoderm mitochondrial gene rearrangements also proved problematic because of extensive variation in gene order between and within classes. A comparison of the two distinctive ophiuroid mitochondrial gene orders supports the hypothesis that O. lütkeni has a more derived mitochondrial gene order versus O. aculeata. The variation in the echinoderm mitochondrial gene maps reinforces the limitations of the application of mitochondrial gene rearrangements as a global phylogenetic tool.

Animals↗
PubMed2000

[Zonation of macrobenthic communities along two bays in an insular coral reef ecosystem (Moorea, French Polynesia)].

Zonation of macrobenthic communities (corals, algae, molluscs, sponges and echinoderms) on fringing reefs was investigated in two bays in a coral reef ecosystem (Moorea, French Polynesia). Species richness, abundance and coral cover, and species richness of macroalgae increased from the bayhead to the bay entrance. For molluscs and sponges, no general trend was observed. Species richness and abundance of echinoderms increased from the head to the entrance of Opunohu Bay, but this trend was less pronounced in Cook Bay. The gradients observed for corals, macroalgae and echinoderms were correlated with one or several of the following abiotic factors: salinity, turbidity, concentration of silicates in surface waters, and concentrations of organic carbon, carbohydrates and amino acids in the sediments. These factors are associated with terrestrial run-off via river discharge that occurs at the bayheads, where the major river is located. The high degree of confinement in the bayheads allowed the establishment of only a few tolerant macrobenthic species. Although the low diversity and abundance of corals and echinoderms seem to be a characteristic of Polynesian bays, a high diversity of corals can be found in the vicinity of the bayheads in coral reefs of the western Pacific.

Animals↗
PubMed2006

Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida.

Deuterostomes comprise vertebrates, the related invertebrate chordates (tunicates and cephalochordates) and three other invertebrate taxa: hemichordates, echinoderms and Xenoturbella. The relationships between invertebrate and vertebrate deuterostomes are clearly important for understanding our own distant origins. Recent phylogenetic studies of chordate classes and a sea urchin have indicated that urochordates might be the closest invertebrate sister group of vertebrates, rather than cephalochordates, as traditionally believed. More remarkable is the suggestion that cephalochordates are closer to echinoderms than to vertebrates and urochordates, meaning that chordates are paraphyletic. To study the relationships among all deuterostome groups, we have assembled an alignment of more than 35,000 homologous amino acids, including new data from a hemichordate, starfish and Xenoturbella. We have also sequenced the mitochondrial genome of Xenoturbella. We support the clades Olfactores (urochordates and vertebrates) and Ambulacraria (hemichordates and echinoderms). Analyses using our new data, however, do not support a cephalochordate and echinoderm grouping and we conclude that chordates are monophyletic. Finally, nuclear and mitochondrial data place Xenoturbella as the sister group of the two ambulacrarian phyla. As such, Xenoturbella is shown to be an independent phylum, Xenoturbellida, bringing the number of living deuterostome phyla to four.

Animals↗
PubMed1998

The mitochondrial genome of the hemichordate Balanoglossus carnosus and the evolution of deuterostome mitochondria.

The complete nucleotide sequence of the mitochondrial genome of the hemichordate Balanoglossus carnosus (acorn worm) was determined. The arrangement of the genes encoding 13 protein, 22 tRNA, and 2 rRNA genes is essentially the same as in vertebrates, indicating that the vertebrate and hemichordate mitochondrial gene arrangement is close to that of their common ancestor, and, thus, that it has been conserved for more than 600 million years, whereas that of echinoderms has been rearranged extensively. The genetic code of hemichordate mitochondria is similar to that of echinoderms in that ATA encodes isoleucine and AGA serine, whereas the codons AAA and AGG, whose amino acid assignments also differ between echinoderms and vertebrates, are absent from the B. carnosus mitochondrial genome. There are three noncoding regions of length 277, 41, and 32 bp: the larger one is likely to be equivalent to the control region of other deuterostomes, while the two others may contain transcriptional promoters for genes encoded on the minor coding strand. Phylogenetic trees estimated from the inferred protein sequences indicate that hemichordates are a sister group of echinoderms.

Animals↗
PubMed1994

Deuterostome phylogeny and the sister group of the chordates: evidence from molecules and morphology.

Complete coding regions of the 18S rRNA gene of an enteropneust hemichordate and an echinoid and ophiuroid echinoderm were obtained and aligned with 18S rRNA gene sequences of all major chordate clades and four outgroups. Gene sequences were analyzed to test morphological character phylogenies and to assess the strength of the signal. Maximum-parsimony analysis of the sequences fails to support a monophyletic Chordata; the urochordates form the sister taxon to the hemichordates, and together this clade plus the echinoderms forms the sister taxon to the cephalochordates plus craniates. Decay, bootstrap, and tree-length distribution analyses suggest that the signal for inference of dueterostome phylogeny is weak in this molecule. Parsimony analysis of morphological plus molecular characters supports both monophyly of echinoderms plus enteropneust hemichordates and a sister group relationship of this clade to chordates. Evolutionary parsimony does not support chordate monophyly. Neighbor-joining, Fitch-Margoliash, and maximum-likelihood analyses support a chordate lineage that is the sister group to an echinoderm-plus-hemichordate lineage. The results illustrate both the limitations of the 18S rRNA molecule alone for high-level phylogeny inference and the importance of considering both molecular and morphological data in phylogeny reconstruction.

Animals↗
PubMed2006

Maternal provisioning in Ophionereis fasciata and O. schayeri: brittle stars with contrasting modes of development.

Evolutionary change from planktotrophic to lecithotrophic development in echinoderms is closely tied to an increase in maternal provisioning. We provide the first data on the major energetic constituents in the eggs of two ophiuroids, the planktotroph Ophionereis fasciata (egg diameter 103 microm) and the lecithotroph O. schayeri (egg diameter 248 microm), to document changes in maternal investment associated with the switch to lecithotrophy in O. schayeri. Lipid classes in the eggs of the two species did not differ except for the presence of small amounts of wax esters in the eggs of O. schayeri. Production of a large egg in O. schayeri is mostly due to enhanced deposition of one energy-storage lipid, triglyceride. The eggs of O. schayeri are not simply scaled-up versions of the ancestral-type eggs of O. fasciata. The relationship between lipid and protein content and egg volume conformed to the relationship previously established for echinoderm eggs. Surprisingly, total lipid and protein data for the eggs of O. schayeri grouped with data for the eggs of planktotrophic echinoderms. The eggs of O. schayeri are small compared with those of other echinoderms with lecithotrophic development, and their energetic contents may approach the minimum provisions necessary to permit development without feeding.

Animals↗
PubMed1999

Bi-penta-bi-decaradial symmetry: A review of evolutionary and developmental trends in holothuroidea (echinodermata)

Holothuroidea, comprising the sea cucumbers, is the least studied class of extant echinoderms, yet this group possesses a wealth of features of potential interest to developmental and evolutionary biologists. Holothuroids include the most morphologically derived echinoderms, including pelagic species and spheroid, plated taxa with mouth and anus adjacent at the end of a long, flexible stalk. To begin investigating this diversity of body form, we first estimated evolutionary relationships in the class Holothuroidea based on maximum parsimony analyses of 1,075 nt of the nuclear small subunit rDNA (for six species in four orders) and on 52 informative morphological characters (for the 25 extant families). Both the morphological and molecular evidence suggests almost an inversion of the prevailing higher level classification. Character-state optimizations indicated that pronounced adult bilateral symmetry evolved three times. In one group even a regain of secondary radial symmetry is found. Respiratory trees, structures unique to holothuroids, are a relatively late innovation, are ectodermally derived, and are bilaterally symmetric, supporting the possibility that the secondary gain of bilateral symmetry in holothuroids is ectodermally derived analogous to, say, the derivation of vertebrate limb dorso-ventral axis. The test of imbricating plates found in 10% of living holothuroids is apparently not homologous with that of other heavily armored echinoderms, evolving much later and at least twice. Indirectly developing larvae, auriculariae, occur in two evolutionarily disparate clades and unlike echinoids comprise a minority of clades. We suggest that this implies the parallel convergent evolution of this larval type or, more speculatively, some form of retention of developmental constraints. J. Exp. Zool. (Mol. Dev. Evol.) 285:93-103, 1999. Copyright 1999 Wiley-Liss, Inc.

Journal Article↗
PubMed1991

Two types of bilateral symmetry in the Metazoa: chordate and bilaterian.

The chordate sagittal plane is perpendicular to the sagittal plane primitive for the bilaterally symmetrical metazoans (Bilateria). The earliest metazoans, when symmetrical at all, were probably radial in symmetry. The axis of symmetry was vertical and the mouth, when present, opened either upward or downward. The Bilateria evolved from the primitive metazoan condition by acquiring bilateral symmetry, mesoderm, a brain at the anterior end and protonephridia. Perhaps in the stem lineage of the Bilateria a hydroid-like or medusoid-like ancestor fell over on one side onto a substrate (pleurothetism). If so, the anteroposterior axis of Bilateria would be homologous with the vertical axis of radial symmetry in coelenterates. The bilaterian plane of symmetry arose to include the anteroposterior axis. The Deuterostomia (the Hemichordata, Echinodermata and Chordata) evolved within the Bilateria by producing the mouth as a secondary perforation. Within the deuterostomes the echinoderms and chordates constitute a monophyletic group named Dexiothetica. Hemichordates retain the primitive bilaterian sagittal plane. The Dexiothetica derive from an ancestor like the present-day hemichordate Cephalodiscus which had lain down on the primitive right side (dexiothetism) and acquired a calcite skeleton. The echinoderms evolved from this ancestor by losing the ancestral locomotory tail and gill slit, becoming static, moving the mouth to the centre of the new upper surface and developing radial pentameral symmetry. The chordates evolved from the same ancestor by developing a notochord in the tail, losing the water vascular system, evolving a filter-feeding pharynx and developing a new vertical plane of bilateral symmetry perpendicular to the old bilaterian plane. Evidence derived from certain bizarre Palaeozoic marine fossils (calcichordates) gives a detailed history of the early evolution of echinoderms and chordates and shows how the new bilateral symmetry was gradually acquired in chordates. This symmetry began in the tail (which contained the notochord and was also the leading end in locomotion) and advanced forward into the head.

Anatomy, Comparative↗
PubMed1997

A PCR survey of hox genes in the sea star, Asterina minor.

The sea star, Asterina minor, was surveyed for Hox genes using the method of PCR and subsequent sequence determination. Seven different Hox-type homeobox fragments and homeobox fragments of two other types, the Gbx-type and the Xlox-type, were identified. The results of comparative analysis with known homeobox sequences suggest that the sea star has only one Hox gene cluster including two genes of the anterior group, four genes of the medial group, and one gene of the posterior group. The existence of a gene of the cognate group 1 has not been known in echinoderm species. Each of the other fragments indicated a definite relationship with one of sea urchin homeoboxes. The hypothetical cluster in the sea star is consistent with the results published for another class of echinoderm, sea urchins, in the putative number of cluster. The present result provides strong evidence that a single Hox cluster is common to echinoderms and its structure in the anterior region is more similar to other deuterostomes than previously thought.

Amino Acid Sequence↗
PubMed2000

Gene conversions may obscure actin gene family relationships.

Phylogenetic hypotheses of muscle actin evolution are significantly different when a sea urchin is used as a representative echinoderm than when a sea star is used. While sea urchin muscle actins support an echinoderm-chordate sister relationship, sea star sequences suggest that echinoderm muscle actins are convergent with chordate muscle actins. Our results suggest that gene conversion in the sea star muscle actin may be responsible for these discordant results.

Actins↗
PubMed2006

Expression patterns of Hox genes in larvae of the sea lily Metacrinus rotundus.

We cloned eight Hox genes (MrHox1, MrHox2, MrHox4, MrHox5, MrHox7, MrHox8, MrHox9/10, and MrHox11/13c) from the sea lily Metacrinus rotundus, a member of the most basal group of the extant echinoderms. At the auricularia stage, before the formation of the pentaradial rudiment, four MrHox genes were expressed sequentially along the anteroposterior (AP) axis in the straightened mesodermal somatocoels in the order MrHox5, MrHox7, MrHox8, and MrHox9/10. The expression of MrHox7 and MrHox8 was detected as early as the hatching stage in the presumptive somatocoel region of the archenteral sac. MrHox5 was expressed in the anteriormost region of the somatocoels, where a stalk-related structure (the chambered organ) forms later. In addition to the mesodermal somatocoels, MrHox7 was expressed in the oral hood ectoderm, which gives rise to the adhesive pit. The expression of four other MrHox genes (MrHox1, MrHox2, MrHox4, and MrHox11/13c) was not detected in any of the larval stages we examined. In comparison with the mesodermal sea urchin Hox genes, the MrHox genes are expressed more posteriorly along the AP (oral-anal) axis than the sea urchin orthologs, implying that the evolution of the eleutherozoans was accompanied by a posteriorization of the larval body. Our study illuminates the possible body plan and Hox expression patterns of the ancestral echinoderm and sheds light on the larval body plan of the last common ancestor of the echinoderms and chordates.

Amino Acid Motifs↗
PubMed2003

Expression and function of a starfish Otx ortholog, AmOtx: a conserved role for Otx proteins in endoderm development that predates divergence of the eleutherozoa.

The sea urchin orthodenticle (Otx)-related transcription factor is an early activator of other endomesodermally expressed transcription factors. Its normal function is required for the development of the archenteron and to lock cells into endomesodermal fate. To determine if this is a basal Otx function in echinoderms we have studied the role of an Otx ortholog in a starfish, Asterina miniata. The patterns of AmOtx expression are found to be similar, in many details, to those reported for other indirectly developing echinoderms and hemichordates, suggestive of a conserved function both in endoderm development and ciliary band formation in these two phyla. When downstream targets of the AmOtx protein are suppressed using a dominant engrailed repressor strategy, embryos fail to develop the endodermal component of the archenteron, though initial phases of mesoderm development proceed normally. The function of Otx proteins in endodermal development at least predated the evolution of the free-living echinoderms (Eleutherozoa).

Alternative Splicing↗
PubMed2006

Nervous system development of the sea cucumber Stichopus japonicus.

The nervous system development of the sea cucumber Stichopus japonicus was investigated to explore the development of the bilateral larval nervous system into the pentaradial adult form typical of echinoderms. The first nerve cells were detected in the apical region of epidermis in the late gastrula. In the auricularia larvae, nerve tracts were seen along the ciliary band. There was a pair of bilateral apical ganglia consisted of serotonergic nerve cells lined along the ciliary bands. During the transition to the doliolaria larvae, the nerve tracts rearranged together with the ciliary bands, but they were not segmented and remained continuous. The doliolaria larvae possessed nerves along the ciliary rings but strongly retained the features of auricularia larvae nerve pattern. The adult nervous system began to develop inside the doliolaria larvae before the larval nervous system disappears. None of the larval nervous system was observed to be incorporated into the adult nervous system with immunohistochemistry. Since S. japonicus are known to possess an ancestral mode of development for echinoderms, these results suggest that the larval nervous system and the adult nervous system were probably formed independently in the last common ancestor of echinoderms.

Animals↗
PubMed2005

Palaeoanatomy and biological affinities of a Cambrian deuterostome (Stylophora).

Stylophora are a peculiar extinct group of asymmetrical deuterostomes whose biological affinity has been fiercely debated. Disarticulated skeletal elements of a ceratocystid stylophoran recovered from the earliest Middle Cambrian of Morocco are not only the oldest stylophorans in the fossil record, but their exceptional preservation provides crucial data on the microstructure of its skeleton. Stylophoran plates are constructed of a three-dimensional mesh, termed 'stereom', identical to that of living echinoderms in which stereom microstructure provides a reliable guide to the nature of the investing soft tissues. Using modern echinoderm anatomy to interpret stereom microstructure of stylophoran elements, here we show that the large proximal lumen of their appendage was filled with muscle and that ligamentary tissues bound distal elements firmly together. We find no evidence for a mouth in the proximal lumen and no evidence that the covering plates of the appendage were articulated. Thus, although skeletal structure suggests that stylophorans are echinoderms, their appendage was not a feeding arm but a muscular locomotory organ.

Animals↗
PubMed2001

Glycobiology of sperm-egg interactions in deuterostomes.

The process of fertilization begins when sperm contact the outermost egg investment and ends with fusion of the two haploid pronuclei in the egg cytoplasm. Many steps in fertilization involve carbohydrate-based molecular recognition between sperm and egg. Although there is conservation of gamete recognition molecules within vertebrates, their homologues have not yet been discovered in echinoderms and ascidians (the invertebrate deuterostomes). In echinoderms, long sulfated polysaccharides act as ligands for sperm receptors. Ascidians employ egg coat glycosides that are recognized by sperm surface glycosidases. Vertebrate egg coats contain zona pellucida (ZP) family glycoproteins, whose carbohydrates bind to sperm receptors. Several candidate sperm receptors for vertebrate ZP proteins have been identified and are discussed here. This brief review focuses on new information concerning fertilization in deuterostomes (the phylogenetic group including echinoderms, ascidians, and vertebrates) and highlights protein-carbohydrate interactions involved in this process.

Animals↗
PubMed2001

Evolutionary dynamics in a novel L2 clade of non-LTR retrotransposons in Deuterostomia.

The evolution of the novel L2 clade of non-long terminal repeat (LTR) retrotransposons and their evolutionary dynamics in Deuterostomia has been examined. The short-term evolution of long interspersed nuclear element 2s (LINE2s) has been studied in 18 reptilian species by analysis of a PCR amplified 0.7-kb fragment encoding the palm/fingers subdomain of reverse transcriptase (RT). Most of the reptilian LINE2s examined are inactive since they contain multiple stop codons, indels, or frameshift mutations that disrupt the RT. Analysis of reptilian LINE2s has shown a high degree of sequence divergence and an unexpectedly large number of deletions. The evolutionary dynamics of LINE2s in reptiles has been found to be complex. LINE2s are shown to form a novel clade of non-LTR retrotransposons that is well separated from the CR1 clade. This novel L2 clade is more widely distributed than previously thought, and new representatives have been discovered in echinoderms, insects, teleost fishes, Xenopus, Squamata, and marsupials. There is an apparent absence of LINE2s from different vertebrate classes, such as cartilaginous fishes, Archosauria (birds and crocodiles), and turtles. Whereas the LINE2s are present in echinoderms and teleost fishes in a conserved form, in most tetrapods only highly degenerated pseudogenes can be found. The predominance of inactive LINE2s in Tetrapoda indicates that, in the host genomes, only inactive copies are still present. The present data indicate that the vertical inactivation of LINE2s might have begun at the time of Tetrapoda origin, 400 MYA. The evolutionary dynamics of the L2 clade in Deuterostomia can be described as a gradual vertical inactivation in Tetrapoda, stochastic loss in Archosauria and turtles, and strict vertical transmission in echinoderms and teleost fishes.

Amino Acid Sequence↗
PubMed1999

A novel ontogenetic pathway in hybrid embryos between species with different modes of development.

To investigate the bases for evolutionary changes in developmental mode, we fertilized eggs of a direct-developing sea urchin, Heliocidaris erythrogramma, with sperm from a closely related species, H. tuberculata, that undergoes indirect development via a feeding larva. The resulting hybrids completed development to form juvenile adult sea urchins. Hybrids exhibited restoration of feeding larval structures and paternal gene expression that have been lost in the evolution of the direct-developing maternal species. However, the developmental outcome of the hybrids was not a simple reversion to the paternal pluteus larval form. An unexpected result was that the ontogeny of the hybrids was distinct from either parental species. Early hybrid larvae exhibited a novel morphology similar to that of the dipleurula-type larva typical of other classes of echinoderms and considered to represent the ancestral echinoderm larval form. In the hybrid developmental program, therefore, both recent and ancient ancestral features were restored. That is, the hybrids exhibited features of the pluteus larval form that is present in both the paternal species and in the immediate common ancestor of the two species, but they also exhibited general developmental features of very distantly related echinoderms. Thus in the hybrids, the interaction of two genomes that normally encode two disparate developmental modes produces a novel but harmonious ontongeny.

Animals↗