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  • 1
    Electronic Resource
    Electronic Resource
    Phylogenetic relationships among extant classes of echinoderms, as inferred from sequences of 18S rDNA, coincide with relationships deduced from the fossil record (1994)
    Springer
    Journal of molecular evolution 38 (1994), S. 41-49 
    Details
    ISSN: 1432-1432
    Keywords: Echinoderms ; Five extant classes ; 18S rDNA ; Molecular phylogeny ; Divergence times ; Fossil record
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In spite of the rich fossil record and multiple descriptions of morphological and embryological characteristics, the origin and subsequent evolution of echinoderms remain highly controversial issues. Using sequence data derived from 18S rDNA, we have investigated the phylogenetic relationships among five extant classes of echinoderms—namely, crinoids, asteroids, ophiuroids, echinoids, and holothurians. Almost complete sequences of 18S rDNA were determined for one species in each class, and phylogenetic trees were constructed both by the neighbor joining method and by the maximum-likelihood method, with a hemichordate as an outgroup. The trees constructed by these methods support the hypothesis that the phylum Echinodermata can be subdivided into two subphyla, Pelmatozoa and Eleutherozoa. The class Holothuroidea, which has been the subject of debate with respect to whether the members are primitive or advanced echinoderms, did not occupy a primitive position but had an affinity for the class Echinoidea. Since both trees gave different branching topologies for the order of emergence of asteroids and ophiuroids, it seems likely that these two groups emerged within a very short period of time. A rough estimate of the timing of the divergence of the five classes from the present molecular analysis coincided with that deduced from the fossil record.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00175494
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  • 2
    Electronic Resource
    Electronic Resource
    Regulated spatial expression of fusion gene constructs with the 5′ upstream region of Halocynthia roretzi muscle actin gene in Ciona savignyi embryos (1993)
    Springer
    Development genes and evolution 203 (1993), S. 104-112 
    Details
    ISSN: 1432-041X
    Keywords: Ascidians ; Muscle actin gene ; Fusion gene construct ; Specific expression ; Muscle lineage cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract pHrMA4a-Z is a recombinant plasmid in which about 1.4 kb of the 5′ flanking region of a gene for muscle actin HrMA4a from the ascidian Halocynthia roretzi is fused with the coding sequence of a bacterial gene for β-galactosidase (lac-Z). In this study, we examined the expression of the fusion gene construct when it was introduced into eggs of another ascidian, namely Ciona savignyi. When a moderate amount of linearized pHrMA4a-Z was introduced into fertilized Ciona eggs, the expression of the reporter gene was evident in muscle cells of the larvae, suggesting that both species share a common machinery for the expression of muscle actin genes. The 5′ upstream region of HrMA4a contains several consensus sequences, including a TATA box at -30, a CArG box at -116 and four E-boxes within a region of 200 bp. A deletion construct, in which only the 216-bp 5′ flanking region of HrMA4a was fused with lac-Z, was expressed primarily in larval muscle cells. However, another deletion construct consisting of only the 61-bp upstream region of HrMA4a fused with lac-Z was not expressed at all. When pHrMA4a-Z or ΔpHrMA4a-Z (−216) was injected into each of the muscle-precursor blastomeres of the 8-cell embryo, expression of the reporter gene was observed in larval muscle cells in a lineage-specific fashion. However, expression of the reporter gene was not observed when the plasmid was injected into non-muscle lineage. Therefore, the expression of the reporter gene may depend on some difference in cytoplasmic constituents between blastomeres of muscle and non-muscle lineage in the 8-cell embyo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539896
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  • 3
    Electronic Resource
    Electronic Resource
    Expression of pharyngeal gill-specific genes in the ascidian Halocynthia roretzi (1996)
    Springer
    Development genes and evolution 206 (1996), S. 218-226 
    Details
    ISSN: 1432-041X
    Keywords: Key words Ascidians ; Pharyngeal gill ; Specific gene expression ; Origin of chordates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The most primitive chordates may have arisen with a shift to internal feeding through the use of the pharyngeal gill slits and endostyle for extracting suspended food from the water. Therefore, the pharyngeal gill and endostyle, in addition to notochord and nerve cord, are structures key to an understanding of the molecular developmental mechanisms underlying the origin and evolution of chordates. In this and a following study, isolation of cDNA clones for genes that are specifically expressed in the pharyngeal gill or endostyle in the ascidian Halocynthia roretzi was attempted. Differential screening of a pharyngeal gill cDNA library and an endostyle cDNA library with total pharyngeal-gill cDNA probes yielded cDNA clones for two pharyngeal gill-specific genes, HrPhG1 and HrPhG2. Northern blot analysis showed a 3.0-kb transcript of HrPhG1 and a 2.0-kb transcript of HrPhG2. Predicted amino acid sequences of the gene products suggested that both genes encode secretory proteins with no significant match to known proteins. In adults, both HrPhG1 and HrPhG2 genes were only expressed in the pharyngeal gill and not in other tissues including the endostyle, body-wall muscle, gonad, gut and digestive gland. HrPhG1 and HrPhG2 transcripts were undetectable in embryos and larvae, and were first detected in juveniles 3 days after initiation of metamorphosis. In situ hybridization revealed that the expression of HrPhG1 and HrPhG2 was restricted to differentiating pharyngeal-wall epithelium, with intense signals in the area surrounding the stigma or gill slit. These genes may serve as probes for further analyses of molecular mechanisms underlying the occurrence of pharyngeal gill and formation of gill slits during chordate evolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050047
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  • 4
    Electronic Resource
    Electronic Resource
    Expression of endostyle-specific genes in the ascidian Halocynthia roretzi (1996)
    Springer
    Development genes and evolution 206 (1996), S. 227-235 
    Details
    ISSN: 1432-041X
    Keywords: Key words Ascidians ; Endostyle ; Specific gene expression ; Origin of chordates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The endostyle is a special organ in the pharynx of Urochordata, Cephalochordata and Cyclostomata. This organ may have arisen in their common ancestor with a shift to internal feeding for extracting suspended food from the water. In addition, the endostyle has functional homology to the vertebrate thyroid gland. The endostyle is therefore another key structure in the understanding of the origin and evolution of chordates. Following a previous report of the pharyngeal gill-specific genes, we report here the isolation and characterization of cDNA clones for endostyle-specific genes HrEnds1 and HrEnds2 of the ascidian Halocynthia roretzi. These cDNA clones were obtained by differential screening of an endostyle cDNA library and a pharyngeal gill cDNA library with total endostyle cDNA probes. Both transcripts were abundant in the library; each represented about 10% of the cDNA clones of the library. The HrEnds1 transcript was small in size, about 600 bp in length. Although the predicted amino acid sequence of the gene product showed no similarity to known proteins, mean hydropathy profiles suggested that HrENDS1 is a type Ib protein or secreted protein. The HrEnds2 transcript was about 2.5 kb in length. Although the HrEnds2 gene product showed no sequence similarity to known proteins, mean hydropathy profiles suggested that HrENDS2 is a secreted protein. The transcripts of both genes were not detected in embryos, larvae and early juveniles but were evident in 1-month-old young adult after several compositional zones were organized in the endostyle. In situ hybridization revealed that distribution of transcripts of both genes was restricted to zone 6, the protein-secreting glandular element of the endostyle. These genes may be useful for further analysis of molecular mechanisms involved in endostyle development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050048
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  • 5
    Electronic Resource
    Electronic Resource
    Specific expression of myosin heavy chain gene in muscle lineage cells of the ascidian embryo (1990)
    Springer
    Development genes and evolution 199 (1990), S. 307-313 
    Details
    ISSN: 1432-041X
    Keywords: Specific gene expression ; Myosin heavy chain ; Muscle lineage cells ; Ascidian embryos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In ascidians the lineage of embryonic precursor cells is well documented. In this study, we investigated temporal and spatial expression of myosin heavy chain (MHC) gene during embryogenesis of the ascidianHalocynthia roretzi. When the occurrence of MHC transcripts was examined by Northern blot hybridization and in situ hybridization with specific cDNA and antisense RNA probes, transcripts were undetectable in fertilized eggs and cleavage-stage embryos. This suggests that the maternal message for MHC is not directly associated with the synthesis of MHC protein in ascidian embryos. MHC transcripts were initially observed at the gastrula stage. In situ hybridization of whole-mount preparations demonstrated that the transcripts first appeared in nuclei of primary-lineage muscle cells of the early-to-middle gastrula and accumulated rapidly as development progressed. The occurrence of MHC transcripts was restricted to differentiating muscle cells. No hybridization signal was detected in mesenchyme cells which are thought to form adult body-wall muscle. After metamorphosis the amount of MHC transcripts decreased; they became undetectable in juveniles about 10 days after metamorphosis, suggesting an intermission of MHC gene activity prior to the formation of adult bodywall muscle. Thus the expression of MHC gene in ascidian embryos was strictly regulated in both spatial and temporal orders and occurred only in muscle lineage cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01709509
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