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At least 19 recordsLinked to original sources
PubMed2001

Brachyury (T) gene expression and notochord development in Oikopleura longicauda (Appendicularia, Urochordata).

Appendicularia (Larvacea) is a subgroup of Urochordata (Tunicata) comprised of holoplanktonic organisms that retain their tailed architecture throughout their life history, while other tunicates, including ascidians and doliolids, resorb the tail after metamorphosis. In order to investigate the characteristics of the appendicularian unresorbed notochord, we isolated a partial genomic clone and a full-length cDNA sequence homologous to the mouse Brachyury (T) gene from the appendicularian Oikopleura longicauda. Brachyury is known to be predominantly expressed in the notochord cells and plays an important role in their differentiation in other chordates. While phylogenetic analysis robustly supports the orthology of the isolated Brachyury gene, the exon-intron organization found in the genomic clone was distinct from that well-conserved among other T-box genes. In addition to a detailed observation of notochord development in living specimens, whole-mount double in situ hybridization was carried out using a Brachyury probe along with a muscle actin probe. The Brachyury transcripts were found in the notochord of the tailbud embryos and persisted into later stages. The present study highlights characteristics of notochord development in the appendicularian. Furthermore, these results provide basic knowledge for comprehensive understanding of the cellular- and molecular-based mechanisms needed to build the characteristic cytoarchitecture of notochord that varies among tunicate species.

Amino Acid Sequence↗
PubMed1998

Neurogenic role of the neural gland in the development of the ascidian, Botryllus schlosseri (Tunicata, Urochordata).

In adult ascidians, the neural complex consists of a cerebral ganglion (the brain) and the associated neural gland. We have studied the development of the neural complex during the vegetative reproduction of the colonial ascidian Botryllus schlosseri, the buds of which arise from the atrial mantle of the parental zooid. Each bud develops into a new organism within which a neural complex becomes differentiated. We found that the presumptive (pioneer) nerve cells that ultimately form the cerebral ganglion of the adult arise as migratory cells from a primordial cluster of rudimentary gland cells. Hence, the neural gland appears to be neurogenic in that it serves as the cellular source of components that differentiate into conventional nerve cells. In the adult, these cells take on the form of a typical invertebrate ganglion with an outer cortex of nerve cell bodies and an internal medulla. This medulla consists of a neuropile of neuronal processes making classical synaptic contacts. The adult neural gland differentiates into a structure with a ciliated duct that opens into the branchial chamber, the body of the gland, and the dorsal organ, which is quite distinct from the dorsal strand of other ascidians. The rudimentary neural gland cells, therefore, differentiate into one of two distinct pathways: the first, glandular, is possibly involved in the evaluation of environmental signals, and the other, nervous, leads to brain formation. This compares with the vertebrate situation in which the olfactory-pituitary placodes are thought to originate from a common cellular source. Thus, these data support the earlier contention of a homology between the tunicate neural gland and the vertebrate adenohypophysis.

Animals↗
PubMed1998

Chemotactic responses of tunicate (Urochordata, Ascidiacea) hemocytes in vitro.

A number of molecules were found to alter the motility of tunicate hemocytes. Bacterial lipopolysaccharide (LPS) significantly enhanced cell mobility relative to non-stimulated controls. Responses to LPS were not directional and so represented chemokinesis. In contrast, checkerboard analyses indicated that two tunicate hemolymph proteins, tunIL1-alpha and -beta, stimulated truly directional chemotaxis by hemocytes. The data suggest that tunIL1 proteins may contribute to defense by altering the localization of immunocompetent cells.

Animals↗
PubMed1982

Occurrence of different secretin-like cells in the digestive tract of the ascidian Styela plicata (Urochordata, Ascidiacea).

Secretin-like cells have been detected in the digestive tract of the ascidian Styela plicata by means of immunofluorescent and immunocytochemical methods. Especially, in the esophageal epithelium there are immunoreactive cells (S2) in which a biogenic amine (5-HT) and a regulatory peptide (secretin) occur together. In the gastric epithelium only secretin-like cells (S1) are present. Tests of cross-reactivity performed with glucagon, GIP and VIP, have confirmed the presence of a secretin-like molecule only in the S1 and S2 cells.

Animals↗
PubMed1977

Glycogen deposits in the pyloric gland of the ascidian Styela clava (Urochordata).

The pyloric gland of Styela clava contains large glycogen deposits that are digested by treatment with alpha amylase and depleted by 15 days starvation. The deposits are surrounded by cytoplasmic regions containing smooth endoplasmic reticulum and mitochondria. The cells also have rough endoplasmic reticulum, Golgi cisterns, lysosomes, microvilli, cilia, and lateral infoldings of the plasma membrane. The fine structure of the pyloric cells and the position of tubules between the absorptive epithelium and general circulation suggest that the gland functions as the vertebrate liver in carbohydrate metabolism. The pyloric cells of Styela do not appear to be excretory in a "renal" sense, since there is no infolding of the basal plasmalemma and mitochondria are usually associated only with the glycogen deposits. However, a hepatic-like excretory role is consistent with current findings. In light of the phylogenic affinities of vertebrates and ascidians, it is possible that the pyloric gland is homologous to the liver.

Animals↗
PubMed2003

Mitochondrial genome of Ciona savignyi (Urochordata, Ascidiacea, Enterogona): comparison of gene arrangement and tRNA genes with Halocynthia roretzi mitochondrial genome.

The complete nucleotide sequence of the urochordate Ciona savignyi (Ascidiacea, Enterogona) mitochondrial (mt) genome (14,737 bp) was determined. The Ciona mt genome does not encode a gene for ATP synthetase subunit 8 but encodes an additional tRNAGly gene (anticodon UCU), as is the case in another urochordate, Halocynthia roretzi (Ascidiacea, Pleurogona), mt genome. In addition, the Ciona mt genome encodes two tRNAMet genes; anticodon CAT and anticodon TAT. The tRNACys gene is thought to lack base pairs at the D-stem. Thus, the Ciona mt genome encodes 12 protein, 2 rRNA, and 24 tRNA genes. The gene arrangement of the Ciona mt genome differs greatly from those of any other metazoan mt genomes reported to date. Only three gene boundaries are shared between the Halocynthia and the Ciona mt genomes. Molecular phylogenetic analyses based on amino acid sequences of mt protein genes failed to demonstrate the monophyly of the chordates.

Animals↗
PubMed1976

Renewal of the gonads in Styela clava (Urochordata: Ascidiacea) as revealed by autoradiography with tritiated thymidine.

DNA-synthesizing cells in the gonads of the ascidian Styela clava were labeled with tritiated thymidine and detected with autoradiography. In the testis, spermatogonia and primary spermatocytes are labeled after 1 hr. Labeled spermatozoa occur in the lumen of the testis follicles after 10 days and in the sperm ducts after 20 days. In the ovary, only germ cells (oogonia and pre-leptotene primary oocytes) and follicle cells are labeled after 1 hr. By 60 days, oocytes with basophilic cytoplasm (15-65 mu in diameter) are labeled; test cells embedded in larger eosinophilic oocytes (150 mu in diameter) are also labeled. Germ cells give rise to both oocytes and follicle cells. Through continued cell division, follicle cells give rise to test cells.

Animals↗
PubMed1988

Bistramide A, a new toxin from the urochordata Lissoclinum bistratum Sluiter: isolation and preliminary characterization.

Two cases of human intoxication caused by the lyophilized powder of Lissoclinum bistratum Sluiter, a New Caledonian ascidian, are reported. The symptoms observed were caused by a substance designated bistramide A (C40H68N2O8) of hitherto unknown chemical structure. Preliminary toxicological investigations indicate that bistramide A may effect the central nervous system, leading to paresthesia and loss of muscle tone. A progressive decrease in cardiac rhythm was also observed in animals. Bistramide A (1.4 x 10(-6) M) did not alter the resting potential of frog heart and skeletal muscle but reduced the amplitude and duration of cardiac action potential and prolonged the interval between action potentials. Bistramide A also has a marked cytotoxic effect on cancer cells KB (IC50 = 4.5 x 10(-8) M) and P 388 (IC50 = 2.0 x 10(-8) M) and on normal endothelial cells (IC50 = 2.2 x 10(-8) M). However, it has not been possible to relate the cytotoxic property to the symptoms of intoxication. Bistramide A may originate from the urochordate itself or from symbiotic algae.

Acetamides↗
PubMed2002

Recent introduction of the dominant tunicate, Pyura praeputialis (Urochordata, Pyuridae) to Antofagasta, Chile.

The large sessile tunicate Pyura stolonifera (Pleurogona: Stolibranchiata: Pyuridae), has been regarded as a complex taxon with disjointed distributions, including Australia (Pyura stolonifera praeputialis), South Africa (Pyura stolonifera stolonifera) and South America (Chile, Antofagasta: Pyura sp., the 'piure de Antofagasta'), and has been cited under at least five taxonomic combinations. The 'piure de Antofagasta' is a competitively dominant species in rocky intertidal habitats and shows a limited geographical range (60-70 km) exclusively inside the Bay of Antofagasta. Using cytochrome oxidase I (COI) mitochondrial sequence data from Pyura specimens of the three taxa we tested whether the Chilean taxon represents: (i) a Gondwana relict; (ii) a more recently divergent species; or (iii) a recently introduced species. The results suggest that the Chilean taxon is a recent introduction to Chile from Australian populations and that Pyura stolonifera praeputialis, from Australia, and the 'piure de Antofagasta' are geographical populations of a single species: Pyura praeputialis; whereas the South African taxon represents a second species: Pyura stolonifera.

Animals↗
PubMed1999

Complete DNA sequence of the mitochondrial genome of the ascidian Halocynthia roretzi (Chordata, Urochordata).

The complete nucleotide sequence of the 14,771-bp-long mitochondrial (mt) DNA of a urochordate (Chordata)-the ascidian Halocynthia roretzi-was determined. All the Halocynthia mt-genes were found to be located on a single strand, which is rich in T and G rather than in A and C. Like nematode and Mytilus edulis mtDNAs, that of Halocynthia encodes no ATP synthetase subunit 8 gene. However, it does encode an additional tRNA gene for glycine (anticodon TCT) that enables Halocynthia mitochondria to use AGA and AGG codons for glycine. The mtDNA carries an unusual tRNA(Met) gene with a TAT anticodon instead of the usual tRNA(Met)(CAT) gene. As in other metazoan mtDNAs, there is not any long noncoding region. The gene order of Halocynthia mtDNA is completely different from that of vertebrate mtDNAs except for tRNA(His)-tRNA(Ser)(GCU), suggesting that evolutionary change in the mt-gene structure is much accelerated in the urochordate line compared with that in vertebrates. The amino acid sequences of Halocynthia mt-proteins deduced from their gene sequences are quite different from those in other metazoans, indicating that the substitution rate in Halocynthia mt-protein genes is also accelerated.

Animals↗
PubMed1986

Tight and gap junctions in the intestinal tract of tunicates (Urochordata): a freeze-fracture study.

The intestinal tracts from seven different species of tunicates, some solitary, some colonial, were studied fine-structurally by freeze-fracture. These urochordates occupy an intermediate position phylogenetically between the vertebrates and the invertebrates. The various regions of their gut were isolated for examination and the junctional characteristics of each part investigated. All the species examined exhibited unequivocal vertebrate-like belts of tight-junctional networks at the luminal border of their intestinal cells. No septate junctions were observed. The tight junctions varied in the number of their component strands and the depth to which they extended basally, some becoming loose and fragmented towards that border. The junctions consisted of ridges or rows of intramembranous particles (IMPs) on the P face, with complementary, but offset, E face grooves into which IMPs sometimes fractured. Tracer studies show that punctate appositions, the thin-section correlate of these ridge/groove systems, are sites beyond which exogenous molecules do not penetrate. These junctions are therefore likely to represent permeability barriers as in the gut tract of higher chordates. Associated with these occluding zonular junctions are intermediate junctions, which exhibit no identifiable freeze-fracture profile, and macular gap junctions, characterized by a reduced intercellular cleft in thin section and by clustered arrays of P face particles in freeze-fractured replicas; these display complementary aggregates of E face pits. The diameters of these maculae are rarely very large, but in certain species (for example, Ciona), they are unusually small. In some tissues, notably those of Diplosoma and Botryllus, they are all of rather similar size, but very numerous. In yet others, such as Molgula, they are polygonal with angular outlines, as might be indicative of the uncoupled state. In many attributes, these various junctions are more similar to those found in the tissues of vertebrates, than to those in the invertebrates, which the adult zooid forms of these lowly chordates resemble anatomically.

Animals↗
PubMed2002

Colony specificity in the xenogeneic combinations among four Botrylloides species (urochordata, ascidiacea).

Xenogeneic rejection reactions were histologically examined among four compound ascidians of the genus Botrylloides; B. simodensis, B. lentus, B. fuscus and B. violaceus, to compare with the allogeneic rejections of these species. When the incompatible conspecifics were brought into contact, hemolytic rejections occurred at the point where the tunic of the two colonies was partially fused. Xenogeneic contact at their growing edges induced hemolytic rejection in some combinations (B. simodensis-B. lentus, B. lentus-B. fuscus, and B. fuscus-B. violaceus), while conspicuous reaction was not found in the other combinations. Since the hemolytic rejection requires the partial fusion of tunic, the occurrence of hemolytic rejection suggests that the tunic cuticle of the colonies does not discriminate the facing colony from conspecifics. On the other hand, whereas cut surface contact between incompatible conspecifics induced intense rejection in B. simodensis, it resulted in fusion (formation of vascular connection) even in the combination in which the growing edge contact resulted in rejection. In xenogeneic combination, the cut surface contact of colonies always resulted in an intense rejection reaction except for B. fuscus-B. violaceus in which hemolytic reactions did not occur. The absence of hemolytic rejection suggests that the effector system for rejection reaction is not activated in this combination. Activity of phenoloxidase, a key enzyme of the rejection reaction, indicates lower reactivity in B. lentus, B. fuscus and B. violaceus than that in B. simodensis.

Alleles↗
PubMed2005

An atrial membrane in the colonial ascidian, Ritterella tokioka Kott, 1992 (Urochordata: Ascidiacea) from Sagami Bay.

An atrial membrane, similar to that previously reported (as a placental membrane) in Placentela crystallina Redikorzev, 1913, has been found in the holotype and other specimens of another aplousobranch ascidian, Ritterella tokioka Kott, 1992 (=R. pedunculata Tokioka, 1953). In serial sections, the membrane is seen to be an extensive fold of the atrial epithelium over the rectum that projects into the atrial cavity and supports developing embryos over its outer surface. The similar states in the atrial membrane seen in the two species are attributable to homoplasy, rather than homology.

Animals↗
PubMed1984

A mono-sited transferrin from a representative deuterostome: the ascidian Pyura stolonifera (subphylum Urochordata).

An iron-binding protein has been found in the plasma of Pyura stolonifera. This protein has a molecular weight of about 41,000 +/- 2,000 and binds 1 mol iron/mol protein. The absorption maxima are lambda = 280 and lambda = 429 nm (E429/E280 = 0.044). Bicarbonate is bound concomitantly with high affinity and is necessary for optimal color formation at lambda = 429 nm. The protein showed a negligible exchange of iron with human apotransferrin under physiologic conditions over two hours. Upon incubation with rat reticulocytes, the protein reacts with membrane receptors for transferrins, and the protein, with its iron, is transported intracellularly where the iron is incorporated into heme. The 59Fe protein, after intravenous injection, disappears rapidly from the plasma and is excreted largely in the urine, with a substantial fraction present in the kidney and another large fraction present in the gut. These findings established the protein as a "transferrin" and support the concept that the larger transferrin molecule in vertebrates, with two iron-binding sites, resulted from a gene duplication.

Animals↗
PubMed2003

CiC3-1a-mediated chemotaxis in the deuterostome invertebrate Ciona intestinalis (Urochordata).

Deuterostome invertebrates possess complement genes, and in limited instances complement-mediated functions have been reported in these organisms. However, the organization of the complement pathway(s), as well as the functions exerted by the cloned gene products, are largely unknown. To address the issue of the presence of an inflammatory pathway in ascidians, we expressed in Escherichia coli the fragment of Ciona intestinalis C3-1 corresponding to mammalian complement C3a (rCiC3-1a) and assessed its chemotactic activity on C. intestinalis hemocytes. We found that the migration of C. intestinalis hemocytes toward rCiC3-1a was dose dependent, peaking at 500 nM, and was specific for CiC3-1a, being inhibited by an anti-rCiC3-1a-specific Ab. As is true for mammalian C3a, the chemotactic activity of C. intestinalis C3-1a was localized to the C terminus, because a peptide representing the 18 C-terminal amino acids (CiC3-1a(59-76)) also promoted hemocyte chemotaxis. Furthermore, the CiC3-1a terminal Arg was not crucial for chemotactic activity, because the desArg peptide (CiC3-1a(59-75)) retained most of the directional hemocyte migration activity. The CiC3-1a-mediated chemotaxis was inhibited by pretreatment of cells with pertussis toxin, suggesting that the receptor molecule mediating the chemotactic effect is G(i) protein coupled. Immunohistochemical analysis with anti-rCiC3-1a-specific Ab and in situ hybridization experiments with a riboprobe corresponding to the 3'-terminal sequence of CiC3-1, performed on tunic sections of LPS-injected animals, showed that a majority of the infiltrating labeled hemocytes were granular amebocytes and compartment cells. Our findings indicate that CiC3-1a mediates chemotaxis of C. intestinalis hemocytes, thus suggesting an important role for this molecule in inflammatory processes.

Amino Acid Sequence↗