Ascidian Tunic Research Articles

Does hair cell differentiation predate the vertebrate appearance?

It is generally accepted that the three main chordate groups (tunicates, cephalochordates and vertebrates) originated from a common ancestor having the basic features of the chordate body plan, i.e. a neural tube and a notochord flanked by striated musculature. There is now increasing evidence that tunicates, rather than cephalochordates, are the vertebrate sister-group. Correlated with this, tunicates have sensory structures similar to those derived from placodes or neural crest in vertebrates. In this context, we discuss here whether the precursors of vertebrate hair cells, which are placodal in origin, were present in ancestral chordates. The ascidian tunicates possess a coronal organ, consisting of a row of mechanosensory cells that runs around the base of the oral siphon. Its function is to monitor the incoming water flow. The cells are secondary sensory cells, i.e. they lack axons and synapse with neurons whose somata lie in the cerebral ganglion. They are accompanied by supporting cells and, as in vertebrates, have varying morphologies in the species so far examined: in one order (Enterogona), they are multiciliate; in the other (Pleurogona), they may possess an apical apparatus, consisting of one or two cilia accompanied by stereovilli, that are graded in length. Coronal cells thus resemble vertebrate hair cells closely in their morphology, embryonic origin and arrangement, which suggests they originated early in ancestral chordates. We are continuing our study of the coronal organ in other ascidian species, and report new data here on Botrylloides leachi, which conforms with the pattern of Pleurogona and, in particular, with previously published results on other botryllid ascidians.

A revised fate map for amphioxus and the evolution of axial patterning in chordates

The chordates include vertebrates plus two groups of invertebrates (the cephalochordates and tunicates). Previous embryonic fate maps of the cephalochordate amphioxus (Branchiostoma) were influenced by preconceptions that early development in amphioxus and ascidian tunicates should be fundamentally the same and that the early amphioxus embryo, like that of amphibians, should have ventral mesoderm. Although detailed cell lineage tracing in amphioxus has not been done because of limited availability of the embryos and because cleavage is radial and holoblastic with the blastomeres nearly equal in size and not tightly adherent until the mid-blastula stage, a compilation of data from gene expression and function, blastomere isolation and dye labeling allows a more realistic fate map to be drawn. The revised fate map is substantially different from that of ascidians. It shows (1) that the anterior pole of the amphioxus embryo is offset dorsally from the animal pole only by about 20°, (2) that the ectoderm/mesendoderm boundary (the future rim of the blastopore) is at the equator of the blastula, which approximately coincides with the 3rd cleavage plane, and (3) that there is no ventral mesoderm during the gastrula stage. Involution or ingression of cells over the blastopore lip is negligible, and the blastopore, which is posterior, closes centripetally as if by a purse string. During the gastrula stage, the animal pole shifts ventrally, coming to lie about 20° ventral to the anterior tip of the late gastrula/early neurula. Comparisons of the embryos of amphioxus and vertebrates indicate that in spite of large differences in the mechanics of cleavage and gastrulation, anterior/posterior and dorsal/ventral patterning occur by homologous genetic mechanisms. Therefore, the small, nonyolky embryo of amphioxus is probably a reasonable approximation of the basal chordate embryo before the evolution of determinate cleavage in the tunicates and the evolution large amounts of yolk in basal vertebrates.

Localization of granulatimide alkaloids in the tissues of the ascidian Didemnum granulatum

Ascidians are a notable source of nitrogen- bearing secondary metabolites with a wide range of biological activities. Although many biologically active compounds have been isolated from ascidians, it is often unclear whether the animal or associated micro- bial symbionts such as bacteria or fungi are the true biosynthetic source of the metabolites. We have addressed the question of the biosynthetic source of the alkaloids granulatimide and isogranulatimides by localizing these compounds within the ascidian. In this work, we demonstrate that granulatimide is stored in Didemnum granulatum tunic bladder cells. Analysis by confocal Xuorescence microscopy at the granulatimide emission range indicated the presence of Xuorescent cells as highly vacuolated cells found dispersed in the ascidian tunic. Since this is the most exposed ascidian tissue, it is possible that these alkaloids may have a protective role, either as sunscreens and/or as feeding

Primary Genetic Linkage Maps of the Ascidian, Ciona intestinalis

For whole-genome analysis in a basal chordate (protochordate), we used F1 pseudo-testcross mapping strategy and amplified fragment length polymorphism (AFLP) markers to construct primary linkage maps of the ascidian tunicate Ciona intestinalis. Two genetic maps consisted of 14 linkage groups, in agreement with the haploid chromosome number, and contained 276 and 125 AFLP loci derived from crosses between British and Neapolitan individuals. The two maps covered 4218.9 and 2086.9 cM, respectively, with an average marker interval of 16.1 and 18.9 cM. We observed a high recombinant ratio, ranging from 25 to 49 kb/cM, which can explain the high degree of polymorphism in this species. Some AFLP markers were converted to sequence tagged sites (STSs) by sequence determination, in order to create anchor markers for the fragmental physical map. Our recombination tools provide basic knowledge of genetic status and whole genome organization, and genetic markers to assist positional cloning in C. intestinalis.

Cell types, microsymbionts, and pyridoacridine distribution in the tunic of three color morphs of the genus Cystodytes (Ascidiacea, Polycitoridae)

Abstract. The tunic of colonial ascidians of the genus Cystodytes is a dynamic and complex system where a variety of cell types and microsymbionts are found. The tunic is also the site where pyridoacridine alkaloids involved in chemical defense are found. We wanted to explore the composition of symbionts and tunic cell types and their relationship with localization of alkaloids in three color morphs (usually attributed to the species Cystodytes dellechiajei). Tunic morphology was studied by means of transmission electron microscopy, and energy‐dispersive X‐ray microanalysis was performed for indirect localization of the bioactive alkaloids produced by these morphotypes. The main cell types identified are bladder cells, pigment cells, amebocytes, phagocytes, and morula cells. Amebocytes include several subtypes that may correspond to a sequence of ontogenetic stages; these cells also seem to give rise to other cell types. In the three morphotypes, the morphology of the tunic and tunic cells is basically the same. The alkaloids are localized in the pigment cells. At least three types of bacteria are present in the tunic, but they are scarce and do not store the targeted bioactive alkaloids. Our results indicate that, although pyridoacridine alkaloids are present in these ascidians, as in a variety of animal phyla, their wide taxonomic range is not necessarily the result of production by common microsymbionts, but rather of the convergent evolution of a successful biosynthetic pathway.

The dopamine‐synthesizing cells in the swimming larva of the tunicate Ciona intestinalis are located only in the hypothalamus‐related domain of the sensory vesicle

Dopamine is a major neuromodulator synthesized by numerous cell populations in the vertebrate forebrain and midbrain. Owing to the simple organization of its larval nervous system, ascidian tunicates provide a useful model to investigate the anatomy, neurogenesis and differentiation of the dopaminergic neural network underlying the stereotypical swimming behaviour of its chordate-type larva. This study provides a high-resolution cellular analysis of tyrosine hydroxylase (TH)-positive and dopamine-positive cells in Ciona intestinalis embryos and larvae. Dopamine cells are present only in the sensory vesicle of the Ciona larval brain, which may be an ancestral chordate feature. The dopamine-positive cells of the ascidian sensory vesicle are located in the expression domain of homologues of vertebrate hypothalamic markers. We show here that the larval coronet cells also arise from this domain. As a similar association between coronet cells and the hypothalamus was reported in bony and cartilaginous fishes, we propose that part of the ascidian ventral sensory vesicle is the remnant of a proto-hypothalamus that may have been present in the chordate ancestor. As dopaminergic cells are specified in the hypothalamus in all vertebrates, we suggest that the mechanisms of dopamine cell specification are conserved in the hypothalamus of Ciona and vertebrates. To test this hypothesis, we have identified new candidate regulators of dopaminergic specification in Ciona based on their expression patterns, which can now be compared with those in vertebrates.

Inferring the feeding habit of the deep-sea ‘big mouth’ ascidian tunicate, Megalodicopia hians, by fatty acid analysis

Colonies of the ‘big mouth’ tunicate, Megalodicopia hians, were first discovered in Toyama Bay, Japan Sea. The suspension-feeding habit of this organism is inferred from the diets in the oral aperture and feces. The colonies were mainly found on the steep slope (water depth > 1 km), particularly at the sites characterized by exposed rocks and/or thin sediment. Most of the individuals faced ‘mouth’ downward, suggesting that they trap suspended matters adrift or re-suspended sediment in the upward current. We have analyzed the composition of total fatty acids of Megalodicopia hians in comparison with those of other bathyal benthic animals having various feeding habits and phylogenies. A dendrogram was constructed by the cluster analysis of the fatty acid compositions. Primary grouping in the fatty acid-based dendrogram reflected the feeding habits rather than the phylogenic relationships of the studied benthic animals. An inference from the dendrogram suggested that suspension-feeding is usual but occasionally this organism engages in the scavenging habit, in general agreement with the inference from the diet analysis.

Aspects of cell production in mantle tissue of Ciona intestinalis L. (Tunicata, Ascidiacea)

Renewal of cell population is needed in the tunic of ascidians, as the tunic cells are involved in many biological functions. Tunic cells are thought to arrive by migrating across the mantle epithelium into the tunic from the blood lacunae or the mesenchymal space. Electron microscope observations show that the mantle epithelium of Ciona intestinalis shares some proliferative characteristics, releasing cells into the tunic and thus providing an increase renewal of tunical cells in restricted zones of adult animals.

Ultraviolet absorption in ascidian tunic and ascidian-Prochloron symbiosis

To characterize the ultraviolet (UV) light-absorbing function of the ascidian tunic, the light absorption spectrum was compared in 22 ascidian species collected from tropical and temperate waters. Non-photosymbiotic ascidians (17 species) had transparent tunics transmitting both visible and UV light, or pigmented or opaque tunics equally absorb both UV and visible light. However, a prominent absorption peak around 320 nm was exclusively found in the colonial ascidians hosting the algal symbiont Prochloron sp., and this absorption peak corresponded to absorption of UV-A (320–400 nm) and UV-B (280–320 nm). The UV-absorbing substances were extracted with methanol. They were mycosporine-like amino acids (MAAs): mycosporine-glycine, palythine, shinorine, and porphyra-334. The MAAs are thought to be synthesized by the shikimic acid pathway that does not occur in animals. Since the isolated Prochloron cells contain MAAs, the symbionts are the most possible candidates as the source of the MAAs in the tunic. In Diplosoma virens, the composition of MAAs was different between isolated Prochloron cells and colony residue from which Prochloron cells were extracted.

The LRIG gene family has three vertebrate paralogs widely expressed in human and mouse tissues and a homolog in Ascidiacea

Human LRIG1 (formerly LIG1), human LRIG2, and mouse Lrig1 (also known as Lig- 1) encode integral membrane proteins. The human genes are located at chromosomes 3p14 and 1p13, which are regions frequently deleted in human cancers. We have searched for additional members of the LRIG family and by molecular cloning identified human LRIG3 and its mouse ortholog Lrig3. Human LRIG3 is located at chromosome 12q13. In silico analysis of public databases revealed a mouse Lrig2 mRNA, three LRIG homologs in the puffer fish Fugu rubripes, and one LRIG homolog in the ascidian tunicate Ciona intestinalis. The human and mouse LRIG polypeptides have the same predicted domain organization: a signal peptide, 15 tandem leucine-rich repeats with cysteine-rich N- and C-flanking domains, three immunoglobulin-like domains, a transmembrane domain, and a cytoplasmic tail. The extracellular part—especially the IgC2.2 domain, the transmembrane domain, and the membrane-proximal part of the cytoplasmic tail—are the most conserved regions. Northern blot analysis and real-time RT-PCR revealed that the three LRIG paralogs are widely expressed in human and mouse tissues. In conclusion, the LRIG gene family was found to have three widely expressed mammalian paralogs, corresponding orthologs in fish, and a homolog in Ascidiacea.

Embryos at the core of life

Writing a textbook on developmental biology is, today, a dangerous task. The amount of data being produced in labs all over the world overwhelms every effort to be up to date, or to be fair to every developmental biologist in the business. Today, the study of developmental biology entails a vast

Preparation and Properties of New Regenerated Cellulose Fibers

New regenerated cellulose fibers are prepared from solution (chemical cellulose con tents, 3, 4.5, 6, and 9 wt%) using N-methylmorpholine-N-oxide (NMMO)/water (87/13 wt%) as a solvent by dry-wet spinning at a winding speed of 20-100 m/min. The chemical cellulose (97% α-cellulose content, 918 DPw, 98% JIS whiteness) used for this study is prepared from ascidian tunicates by a modified pulping process described in our previous work. The effects of cellulose content and spinning speed on the structure and mechanical properties of fibers are investigated. As the cellulose content increases, the birefringence, crystallinity, and initial tensile modulus of the fibers increase significantly. While the tenacity of the fibers increases with increasing cellulose content up to 6 wt%, there is a great decrease in the tenacity at 9 wt%. That decrease is due to fiber defects. Mechanical properties increase with increasing winding speed. The regenerated cellulosic fibers prepared in this study have a higher ratio of wet strength to dry strength compared to regenerated cellulose fibers produced all over the world.

The Ciona intestinalis genome: when the constraints are off.

The recent genome sequencing of a non-vertebrate deuterostome, the ascidian tunicate Ciona intestinalis, makes a substantial contribution to the fields of evolutionary and developmental biology.1 Tunicates have some of the smallest bilaterian genomes, embryos with relatively few cells, fixed lineages and early determination of cell fates. Initial analyses of the C. intestinalis genome indicate that it has been evolving rapidly. Comparisons with other bilaterians show that C. intestinalis has lost a number of genes, and that many genes linked together in most other bilaterians have become uncoupled. In addition, a number of independent, lineage-specific gene duplications have been detected. These new results, although interesting in themselves, will take on a deeper significance once the genomes of additional invertebrate deuterostomes (e.g. echinoderms, hemichordates and amphioxus) have been sequenced. With such a broadened database, comparative genomics can begin to ask pointed questions about the relationship between the evolution of genomes and the evolution of body plans.

우렁쉥이 껍질로부터 정제한 식이섬유 급여 Rat의 영양학적 특성 및 혈청지질함량의 변화

우렁쉥이 껍질로부터 정제한 식이섬유 급여 Rat의 영양학적 특성 및 혈청지질함량의 변화

GALVANIC EFFECTS OF VARIOUS METALLIC COUPLES ON MARINE BIOFOULING IN A CORAL REEF ENVIRONMENT

Galvanic couples consisting of rings of commercial copper, aluminum 6061 and brass 70Cu/30Zn were directly connected to the following metal plates: UNS S30403, S31603 and S31254 stainless steels, UNS R52400 and R53400 titanium alloys, zirconium 705, UNS N10276 nickel based superalloys and commercial copper. The ring-plate couples were immersed in the coral reef environment in the Red Sea, Eilat, at a depth of 6 meters for a period of one month during December 2000. X-ray diffraction of the metallic surfaces connected to aluminum 6061 rings detected enhanced electro-chemical calcification of calcium carbonate in the crystalline structure of aragonite and calcite. No biofouling was observed on commercial copper and brass 70Cu/30Zn rings. Weight loss was detected in commercial copper and brass 70Cu/30Zn rings and colored corrosion products were observed on the surfaces. The metal plates that were connected to commercial copper and brass 70Cu/30Zn rings were covered with non-adhesive sand and a small amount of biofouling organisms such as tube worms, ascidian tunicate and in one case a runner-like bryozoans (Aetea truncata). In galvanic couples with commercial copper and brass 70Cu/30Zn rings, the copper alloys acted as anodes and the metals alloys plates as cathodes. A biocidic effect of the dissolved copper ions in the near environment including the connected metal plates was detected. In all the cases of galvanic couples consisting of aluminum 6061 rings that were directly connected to the alloy plates, heavy marine biofouling was observed. Enhanced electro-chemical precipitation of calcium carbonate in a crystalline form of aragonite and calcite was observed on all the metallic surfaces. Bryozoans of various species were the main recruits observed on aluminum galvanic couples. Other sessile organisms were identified as ascidian tunicate and filamentous algae.

Preparation and properties of chemical cellulose from ascidian tunic and their regenerated cellulose fibers

AbstractChemical cellulose (dissolving pulp) was prepared from ascidian tunic by modified paper‐pulp process (prehydrolysis with acidic aqueous solution of H2SO4, digestion with alkali aqueous solution of NaOH/Na2S, bleaching with aqueous NaOCl solution, and washing with acetone/water). The α‐ cellulose content and the degree of polymerization (DPw) of the chemical cellulose was about 98 wt % and 918, respectively. The Japanese Industrial Standard (JIS) whiteness of the chemical cellulose was about 98%. From the X‐ray diffraction patterns and 13C‐NMR spectrum, it was found that the chemical cellulose obtained here has cellulose Iβ crystal structure. A new regenerated cellulose fiber was prepared from the chemical cellulose by dry–wet spinning using N‐methylmorpholine‐ N‐oxide (NMMO)/water (87/13 wt %) as solvent. The new regenerated cellulose fiber prepared in this study has a higher ratio of wet‐to‐dry strength (<0.97) than commercially regenerated cellulose fibers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1634–1643, 2002.

Localization studies of ioactive cyclic peptides in the ascidian Lissoclinum patella.

A Palauan specimen of the ascidian Lissoclinum patella contained the cyclic peptides patellamides A-C. In contrast to previous reports concerning the location of cyclic peptides in L. patella and L. bistratum, it has been demonstrated that these cyclic peptides were not located in the symbiotic cyanobacterium Prochloron sp. but were instead distributed throughout the ascidian tunic. The relevance of these results with respect to the biosynthetic origins of the patellamides is discussed.

Evolution of neural crest and placodes: amphioxus as a model for the ancestral vertebrate?

Recent studies of protochordates (ascidian tunicates and amphioxus) have given insights into possible ancestors of 2 of the characteristic features of the vertebrate head: neural crest and placodes. The neural crest probably evolved from cells on either side of the neural plate-epidermis boundary in a protochordate ancestral to the vertebrates. In amphioxus, homologues of several vertebrate neural crest marker genes (BMP2/4, Pax3/7, Msx, Dll and Snail) are expressed at the edges of the neural plate and/or adjacent nonneural ectoderm. Some of these markers are also similarly expressed in tunicates. In protochordates, however, these cells, unlike vertebrate neural crest, neither migrate as individuals through embryonic tissues nor differentiate into a wide spectrum of cell types. Therefore, while the protochordate ancestor of the vertebrates probably had the beginnings of a genetic programme for neural crest formation, this programme was augmented in the earliest vertebrates to attain definitive neural crest. Clear homologues of vertebrate placodes are lacking in protochordates. However, both amphioxus and tunicates have ectodermal sensory cells. In tunicates these are all primary neurons, sending axons to the central nervous system, while in amphioxus, the ectodermal sensory cells include both primary neurons and secondary neurons lacking axons. Comparisons of developmental gene expression suggest that the anterior ectoderm in amphioxus may be homologous to the vertebrate olfactory placode, the only vertebrate placode with primary, not secondary, neurons. Similarly, biochemical, morphological and gene expression data suggest that amphioxus and tunicates also have homologues of the adenohypophysis, one of the few vertebrate structures derived from nonneurogenic placodes. In contrast, the origin of the other vertebrate placodes is very uncertain.

Acid Containers and Cellular Networks in the Ascidian Tunic with Special Remarks on Ascidian Phylogeny

Tunic is a unique integument that contains cellulosic components and various types of free cells (tunic cells), and this tissue is exclusively found in the subphylum Urochordata (= Tunicata). In order to discuss the ascidian phylogeny, the presence or absence of the two characteristic types of tunic cells (tunic bladder cells and the tunic net cells) are examined in 65 ascidian species covering 11 families out of the 15 recognized ones. The tunic bladder cells are exclusively distributed in the species of Didemnidae, Holozoinae, Diazoninae, and Ascidiidae. The species of Corellidae have hemocytes, giant cells, that are very similar to the bladder cells, but these cells are not distributed in the tunic. The tunic pH of these species is usually acidic, because the tunic bladder cells contain strong acid in the vacuoles. The tunic net cells are found in Polyclinidae, Polycitorinae, and Didemnidae. The tunic rounding assay suggests that the tunic net cells may be involved in the contraction of the tunic at least in the species of Polyclinidae and Polycitorinae. If these types of tunic cells can be considered as synapomorphic characters, the character-state distribution suggests that the suborders Phlebobranchia and Aplousobranchia are not monophyletic groups.

Evolution of neural crest and placodes: amphioxus as a model for the ancestral vertebrate?

abstractRecent studies of protochordates (ascidian tunicates and amphioxus) have given insights into possible ancestors of 2 of the characteristic features of the vertebrate head: neural crest and placodes. The neural crest probably evolved from cells on either side of the neural plate–epidermis boundary in a protochordate ancestral to the vertebrates. In amphioxus, homologues of several vertebrate neural crest marker genes (BMP2/4, Pax3/7, Msx, Dll and Snail) are expressed at the edges of the neural plate and/or adjacent nonneural ectoderm. Some of these markers are also similarly expressed in tunicates. In protochordates, however, these cells, unlike vertebrate neural crest, neither migrate as individuals through embryonic tissues nor differentiate into a wide spectrum of cell types. Therefore, while the protochordate ancestor of the vertebrates probably had the beginnings of a genetic programme for neural crest formation, this programme was augmented in the earliest vertebrates to attain definitive neural crest. Clear homologues of vertebrate placodes are lacking in protochordates. However, both amphioxus and tunicates have ectodermal sensory cells. In tunicates these are all primary neurons, sending axons to the central nervous system, while in amphioxus, the ectodermal sensory cells include both primary neurons and secondary neurons lacking axons. Comparisons of developmental gene expression data suggest that the anterior ectoderm in amphioxus may be homologous to the vertebrate olfactory placode, the only vertebrate placode with primary, not secondary, neurons. Similarly, biochemical, morphological and gene expression suggest that amphioxus and tunicates also have homologues of the adenohypophysis, one of the few vertebrate structures derived from nonneurogenic placodes. In contrast, the origin of the other vertebrate placodes is very uncertain.