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Current Topics in Developmental Biology 2020Tunicates are a diverse group of invertebrate marine chordates that includes the larvaceans, thaliaceans, and ascidians. Because of their unique evolutionary position as... (Review)
Review
Tunicates are a diverse group of invertebrate marine chordates that includes the larvaceans, thaliaceans, and ascidians. Because of their unique evolutionary position as the sister group of the vertebrates, tunicates are invaluable as a comparative model and hold the promise of revealing both conserved and derived features of chordate gastrulation. Descriptive studies in a broad range of tunicates have revealed several important unifying traits that make them unique among the chordates, including invariant cell lineages through gastrula stages and an overall morphological simplicity. Gastrulation has only been studied in detail in ascidians such as Ciona and Phallusia, where it involves a simple cup-shaped gastrula driven primarily by endoderm invagination. This appears to differ significantly from vertebrate models, such as Xenopus, in which mesoderm convergent extension and epidermal epiboly are major contributors to involution. These differences may reflect the cellular simplicity of the ascidian embryo.
Topics: Animals; Body Patterning; Cell Lineage; Embryo, Nonmammalian; Endoderm; Evolution, Molecular; Gastrula; Gastrulation; Gene Expression Regulation, Developmental; Morphogenesis; Urochordata
PubMed: 31959289
DOI: 10.1016/bs.ctdb.2019.09.001 -
Current Biology : CB Oct 2020The appendicularian tunicate Oikopleura epitomizes the degree to which evolution can constrain both genome and cellular composition, while at the same time unleashing...
The appendicularian tunicate Oikopleura epitomizes the degree to which evolution can constrain both genome and cellular composition, while at the same time unleashing fantastic specializations.
Topics: Animals; Brain; Genome; Movement; Polysaccharides; Urochordata
PubMed: 33080189
DOI: 10.1016/j.cub.2020.07.075 -
Current Biology : CB Feb 2016Tunicates, also called urochordates, are an extremely diverse subphylum of the Chordata, a phylum that also contains the vertebrates and cephalochordates. The tunicates...
Tunicates, also called urochordates, are an extremely diverse subphylum of the Chordata, a phylum that also contains the vertebrates and cephalochordates. The tunicates seem to have undergone especially rapid evolution: while remaining exclusively marine, they have radiated to occupy habitats ranging from shallow water, to near shore to the open ocean and the deep sea. Furthermore, they have evolved a variety of remarkable reproductive strategies, combining asexual and sexual modes of reproduction that allow for very rapid expansion of populations. An outstanding question is what happened to allow tunicates to evolve so much faster than their nearest relatives, cephalochordates and vertebrates.
Topics: Animals; Biological Evolution; Phylogeny; Reproduction; Urochordata
PubMed: 26906481
DOI: 10.1016/j.cub.2015.12.024 -
Developmental Biology Apr 2019The elongation of embryo and tissue is a key morphogenetic event in embryogenesis and organogenesis. Notochord, a typical chordate organ, undergoes elongation to perform... (Review)
Review
The elongation of embryo and tissue is a key morphogenetic event in embryogenesis and organogenesis. Notochord, a typical chordate organ, undergoes elongation to perform its regulatory roles and to form the structural support in the embryo. Notochord elongation is morphologically similar across all chordates, but ascidian has evolved distinct molecular and cellular processes. Here, we summarize the current understanding of ascidian notochord elongation. We divide the process into three phases and discuss the underlying molecular mechanisms in each phase. In the first phase, the notochord converges and extends through invagination and mediolateral intercalation, and partially elongates to form a single diameter cell column along the anterior-posterior axis. In the second phase, a cytokinesis-like actomyosin ring is constructed at the equator of each cell and drives notochord to elongate approximately two-fold. The molecular composition and architecture of the ascidian notochord contractile ring are similar to that of the cytokinetic ring. However, the notochord contractile ring does not impose cell division but only drives cell elongation followed by disassembly. We discuss the self-organizing property of the circumferential actomyosin ring, and why it disassembles when certain notochord length is achieved. The similar ring structures are also present in the elongation process of other organs in evolutionarily divergent animals such as Drosophila and C. elegans. We hereby propose that actomyosin ring-based circumferential contraction is a common mechanism adopted in diverse systems to drive embryo and tissue elongation. In the third phase, the notochord experiences tubulogenesis and the endothelial-like cells crawl bi-directionally on the notochord sheath to further lengthen the notochord. In this review, we also discuss extracellular matrix proteins, notochord sheath, and surrounding tissues that may contribute to notochord integrity and morphogenesis.
Topics: Actomyosin; Animals; Biological Evolution; Cell Movement; Models, Biological; Notochord; Urochordata
PubMed: 30458170
DOI: 10.1016/j.ydbio.2018.11.009 -
Molecules (Basel, Switzerland) Dec 2022Meridianins are a family of indole alkaloids derived from Antarctic tunicates with extensive pharmacological activities. A series of meridianin derivatives had been... (Review)
Review
Meridianins are a family of indole alkaloids derived from Antarctic tunicates with extensive pharmacological activities. A series of meridianin derivatives had been synthesized by drug researchers. This article reviews the extraction and purification methods, biological activities and pharmacological applications, pharmacokinetic characters and chemical synthesis of meridianins and their derivatives. And prospects on discovering new bioactivities of meridianins and optimizing their structure for the improvement of the ADMET properties are provided.
Topics: Animals; Indole Alkaloids; Urochordata; Antarctic Regions
PubMed: 36557848
DOI: 10.3390/molecules27248714 -
Integrative and Comparative Biology Sep 2021Ascidians are invertebrate chordates, with swimming chordate tadpole larvae that have distinct heads and tails. The head contains the small brain, sensory organs,... (Review)
Review
Ascidians are invertebrate chordates, with swimming chordate tadpole larvae that have distinct heads and tails. The head contains the small brain, sensory organs, including the ocellus (light) and otolith (gravity) and the presumptive endoderm, while the tail has a notochord surrounded by muscle cells and a dorsal nerve cord. One of the chordate features is a post-anal tail. Ascidian tadpoles are nonfeeding, and their tails are critical for larval locomotion. After hatching the larvae swim up toward light and are carried by the tide and ocean currents. When competent to settle, ascidian tadpole larvae swim down, away from light, to settle and metamorphose into a sessile adult. Tunicates are classified as chordates because of their chordate tadpole larvae; in contrast, the sessile adult has a U-shaped gut and very derived body plan, looking nothing like a chordate. There is one group of ascidians, the Molgulidae, where many species are known to have tailless larvae. The Swalla Lab has been studying the evolution of tailless ascidian larvae in this clade for over 30 years and has shown that tailless larvae have evolved independently several times in this clade. Comparison of the genomes of two closely related species, the tailed Molgula oculata and tailless Molgula occulta reveals much synteny, but there have been multiple insertions and deletions that have disrupted larval genes in the tailless species. Genomics and transcriptomics have previously shown that there are pseudogenes expressed in the tailless embryos, suggesting that the partial rescue of tailed features in their hybrid larvae is due to the expression of intact genes from the tailed parent. Yet surprisingly, we find that the notochord gene regulatory network is mostly intact in the tailless M. occulta, although the notochord does not converge and extend and remains as an aggregate of cells we call the "notoball." We expect that eventually many of the larval gene networks will become evolutionarily lost in tailless ascidians and the larval body plan abandoned, with eggs developing directly into an adult. Here we review the current evolutionary and developmental evidence on how the molgulids lost their tails.
Topics: Animals; Biological Evolution; Larva; Notochord; Tail; Urochordata
PubMed: 33881514
DOI: 10.1093/icb/icab022 -
Methods in Molecular Biology (Clifton,... 2011Ascidians, such as Ciona, are invertebrate chordates with simple embryonic body plans and small, relatively non-redundant genomes. Ciona genetics is in its infancy...
Ascidians, such as Ciona, are invertebrate chordates with simple embryonic body plans and small, relatively non-redundant genomes. Ciona genetics is in its infancy compared to many other model systems, but it provides a powerful method for studying this important vertebrate outgroup. Here we give basic methods for genetic analysis of Ciona, including protocols for controlled crosses both by natural spawning and by the surgical isolation of gametes; the identification and propagation of mutant lines; and strategies for positional cloning.
Topics: Animals; Chromosome Mapping; Cloning, Molecular; Cryopreservation; DNA; DNA Mutational Analysis; Female; Fertilization in Vitro; Genetic Techniques; Hybridization, Genetic; Larva; Male; Microinjections; Mutation; Polymerase Chain Reaction; Polymorphism, Single Nucleotide; Urochordata
PubMed: 21805273
DOI: 10.1007/978-1-61779-210-6_15 -
Proceedings of the National Academy of... Jun 2016
Topics: Animals; Base Sequence; Enhancer Elements, Genetic; Transcription Factors; Urochordata
PubMed: 27247414
DOI: 10.1073/pnas.1606109113 -
PloS One 2011The class Ascidiacea presents fundamental opportunities for research in the fields of development, evolution, ecology, natural products and more. This review provides a... (Review)
Review
The class Ascidiacea presents fundamental opportunities for research in the fields of development, evolution, ecology, natural products and more. This review provides a comprehensive overview of the current knowledge regarding the global biodiversity of the class Ascidiacea, focusing in their taxonomy, main regions of biodiversity, and distribution patterns. Based on analysis of the literature and the species registered in the online World Register of Marine Species, we assembled a list of 2815 described species. The highest number of species and families is found in the order Aplousobranchia. Didemnidae and Styelidae families have the highest number of species with more than 500 within each group. Sixty percent of described species are colonial. Species richness is highest in tropical regions, where colonial species predominate. In higher latitudes solitary species gradually contribute more to the total species richness. We emphasize the strong association between species richness and sampling efforts, and discuss the risks of invasive species. Our inventory is certainly incomplete as the ascidian fauna in many areas around the world is relatively poorly known, and many new species continue to be discovered and described each year.
Topics: Animals; Biodiversity; Geography; Guam; Hawaii; Panama; Urochordata
PubMed: 21701684
DOI: 10.1371/journal.pone.0020657 -
Dalton Transactions (Cambridge, England... Feb 2014Cyclic pseudo-peptides derived from marine metabolites of the genus Lissoclinum bistratum and Lissoclinum patella have attracted scientific interest in the last two... (Review)
Review
Cyclic pseudo-peptides derived from marine metabolites of the genus Lissoclinum bistratum and Lissoclinum patella have attracted scientific interest in the last two decades. Their structural properties and solution dynamics have been analyzed in detail, elaborate synthetic procedures for the natural products and synthetic derivatives developed, the biosynthetic pathways studied and it now is possible to produce them biosynthetically. Initially, these macrocyclic ligands were studied due to their medicinal and pharmaceutical potential - some of the isolated cyclic pseudo-peptides show high cytotoxic and antiviral activity. A major focus in the last decade has been on their Cu(II) coordination chemistry, as a number of studies have indicated that dinuclear Cu(II) complexes of cyclic peptides may be involved in the ascidians' metabolism, and this is the focus of the present review.
Topics: Animals; Binding Sites; Coordination Complexes; Copper; Models, Molecular; Peptides, Cyclic; Urochordata
PubMed: 24202205
DOI: 10.1039/c3dt52664j