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Kevin J Peterson - One of the best experts on this subject based on the ideXlab platform.

  • testing putative hemichordate homologues of the chordate dorsal nervous system and endostyle expression of nk2 1 ttf 1 in the acorn worm ptychodera flava hemichordata ptychoderidae
    Evolution & Development, 2002
    Co-Authors: Carter M Takacs, Kevin J Peterson
    Abstract:

    SUMMARY Recent phylogenetic investigations have confirmed that hemichordates and echinoderms are sister taxa. However, hemichordates share several cardinal characteristics with chordates and are thus an important taxon for testing hypotheses of homology between key chordate characters and their putative hemichordate antecedents. The chordate dorsal nervous system (DNS) and endostyle are intriguing characters because both hemichordate larval and adult structures have been hypothesized as homologues. This study attempts to test these purported homologies through examination of the expression pattern of a Ptychodera flava NK2 gene, PfNK2.1, because this gene is expressed both in the DNS and endostyle/thyroid in a wide range of chordate taxa. We found that PfNK2.1 is expressed in both neuronal and pharyngeal structures, but its expression pattern is broken up into distinct embryonic and juvenile phases. During embryogenesis, PfNK2.1 is expressed in the apical ectoderm, with transcripts later detected in presumable neuronal structures, including the apical organ and ciliated feeding band. In the developing juvenile we detected PfNK2.1 signal throughout the pharynx, including the Stomochord, and later in the hindgut. We conclude that the similar utilization of NK2.1 in apical organ development and chordate DNS is probably due to a more general role for NK2.1 in neurogenesis and that hemichordates do not possess a homologue of the chordate DNS. In addition, we conclude that P. flava most likely does not possess a true endostyle; rather during the evolution of the endostyle NK2.1 was recruited from its more general role in pharynx development.

  • Testing putative hemichordate homologues of the chordate dorsal nervous system and endostyle: expression of NK2.1 (TTF‐1) in the acorn worm Ptychodera flava (Hemichordata, Ptychoderidae)
    Evolution & Development, 2002
    Co-Authors: Carter M Takacs, Kevin J Peterson
    Abstract:

    SUMMARY Recent phylogenetic investigations have confirmed that hemichordates and echinoderms are sister taxa. However, hemichordates share several cardinal characteristics with chordates and are thus an important taxon for testing hypotheses of homology between key chordate characters and their putative hemichordate antecedents. The chordate dorsal nervous system (DNS) and endostyle are intriguing characters because both hemichordate larval and adult structures have been hypothesized as homologues. This study attempts to test these purported homologies through examination of the expression pattern of a Ptychodera flava NK2 gene, PfNK2.1, because this gene is expressed both in the DNS and endostyle/thyroid in a wide range of chordate taxa. We found that PfNK2.1 is expressed in both neuronal and pharyngeal structures, but its expression pattern is broken up into distinct embryonic and juvenile phases. During embryogenesis, PfNK2.1 is expressed in the apical ectoderm, with transcripts later detected in presumable neuronal structures, including the apical organ and ciliated feeding band. In the developing juvenile we detected PfNK2.1 signal throughout the pharynx, including the Stomochord, and later in the hindgut. We conclude that the similar utilization of NK2.1 in apical organ development and chordate DNS is probably due to a more general role for NK2.1 in neurogenesis and that hemichordates do not possess a homologue of the chordate DNS. In addition, we conclude that P. flava most likely does not possess a true endostyle; rather during the evolution of the endostyle NK2.1 was recruited from its more general role in pharynx development.

  • A comparative molecular approach to mesodermal patterning in basal deuterostomes: the expression pattern of Brachyury in the enteropneust hemichordate Ptychodera flava
    Development (Cambridge England), 1999
    Co-Authors: Kevin J Peterson, Kunifumi Tagawa, R. A. Cameron, Nori Satoh, Eric H. Davidson
    Abstract:

    This work concerns the formation of mesoderm in the development of an enteropneust hemichordate, Ptychodera flava, and the expression of the Brachyury gene during this process. Brachyury expression occurs in two distinct phases. In the embryo, Brachyury is transcribed during gastrulation in the future oral and anal regions of the gut, but transcripts are no longer detected by 2 weeks of development. Brachyury expression is not detected during the 5 months of larval planktonic existence. During this time, the adult coeloms begin to develop, originating as coalescences of cells that appear to delaminate from the wall of the gut. Brachyury expression cannot be detected again until metamorphosis, when transcripts appear in the mesoderm of the adult proboscis, collar and the very posterior region of the trunk. It is also expressed in the posterior end of the gut. At no time is Brachyury expressed in the Stomochord, the putative homologue of the chordate notochord. These observations illuminate the process of maximal indirect development in Ptychodera and, by comparison with patterns of Brachyury expression in the indirect development of echinoderms, their sister group, they reveal the evolutionary history of Brachyury utilization in deuterostomes.

Carter M Takacs - One of the best experts on this subject based on the ideXlab platform.

  • testing putative hemichordate homologues of the chordate dorsal nervous system and endostyle expression of nk2 1 ttf 1 in the acorn worm ptychodera flava hemichordata ptychoderidae
    Evolution & Development, 2002
    Co-Authors: Carter M Takacs, Kevin J Peterson
    Abstract:

    SUMMARY Recent phylogenetic investigations have confirmed that hemichordates and echinoderms are sister taxa. However, hemichordates share several cardinal characteristics with chordates and are thus an important taxon for testing hypotheses of homology between key chordate characters and their putative hemichordate antecedents. The chordate dorsal nervous system (DNS) and endostyle are intriguing characters because both hemichordate larval and adult structures have been hypothesized as homologues. This study attempts to test these purported homologies through examination of the expression pattern of a Ptychodera flava NK2 gene, PfNK2.1, because this gene is expressed both in the DNS and endostyle/thyroid in a wide range of chordate taxa. We found that PfNK2.1 is expressed in both neuronal and pharyngeal structures, but its expression pattern is broken up into distinct embryonic and juvenile phases. During embryogenesis, PfNK2.1 is expressed in the apical ectoderm, with transcripts later detected in presumable neuronal structures, including the apical organ and ciliated feeding band. In the developing juvenile we detected PfNK2.1 signal throughout the pharynx, including the Stomochord, and later in the hindgut. We conclude that the similar utilization of NK2.1 in apical organ development and chordate DNS is probably due to a more general role for NK2.1 in neurogenesis and that hemichordates do not possess a homologue of the chordate DNS. In addition, we conclude that P. flava most likely does not possess a true endostyle; rather during the evolution of the endostyle NK2.1 was recruited from its more general role in pharynx development.

  • Testing putative hemichordate homologues of the chordate dorsal nervous system and endostyle: expression of NK2.1 (TTF‐1) in the acorn worm Ptychodera flava (Hemichordata, Ptychoderidae)
    Evolution & Development, 2002
    Co-Authors: Carter M Takacs, Kevin J Peterson
    Abstract:

    SUMMARY Recent phylogenetic investigations have confirmed that hemichordates and echinoderms are sister taxa. However, hemichordates share several cardinal characteristics with chordates and are thus an important taxon for testing hypotheses of homology between key chordate characters and their putative hemichordate antecedents. The chordate dorsal nervous system (DNS) and endostyle are intriguing characters because both hemichordate larval and adult structures have been hypothesized as homologues. This study attempts to test these purported homologies through examination of the expression pattern of a Ptychodera flava NK2 gene, PfNK2.1, because this gene is expressed both in the DNS and endostyle/thyroid in a wide range of chordate taxa. We found that PfNK2.1 is expressed in both neuronal and pharyngeal structures, but its expression pattern is broken up into distinct embryonic and juvenile phases. During embryogenesis, PfNK2.1 is expressed in the apical ectoderm, with transcripts later detected in presumable neuronal structures, including the apical organ and ciliated feeding band. In the developing juvenile we detected PfNK2.1 signal throughout the pharynx, including the Stomochord, and later in the hindgut. We conclude that the similar utilization of NK2.1 in apical organ development and chordate DNS is probably due to a more general role for NK2.1 in neurogenesis and that hemichordates do not possess a homologue of the chordate DNS. In addition, we conclude that P. flava most likely does not possess a true endostyle; rather during the evolution of the endostyle NK2.1 was recruited from its more general role in pharynx development.

Thomas Bartolomaeus - One of the best experts on this subject based on the ideXlab platform.

  • Ultrastructure of the Stomochord and the heart–glomerulus complex in Rhabdopleura compacta (Pterobranchia): phylogenetic implications
    Zoomorphology, 2003
    Co-Authors: Georg Mayer, Thomas Bartolomaeus
    Abstract:

    Pterobranchia and Enteropneusta traditionally form the highest ranking sister taxa within the Hemichordata. The most prominent feature of all representatives of the Hemichordata is the Stomochord, which is associated with an anterior excretory complex. The Stomochord has been homologized with the notochord of the Chordata species, though this hypothesis is still under debate. Recently, even the validity and position of the Pterobranchia and the Hemichordata has been doubted. These uncertainties are along with a lack of information on the Rhabdopleurida, one of the highest ranking taxa within the Pterobranchia. This study analyzes the Stomochord and the heart–glomerulus complex of Rhabdopleura compacta on the ultrastructural level. The data confirm that a glomerulus exists in representatives of the Rhabdopleurida, which previously was only known from the Cephalodiscida, the second highest ranking Pterobranchia taxon. The heart–glomerulus complex is, as expected, associated with the Stomochord. Consisting of monociliated, non-vacuolated cells that form a monolayered epithelium of presumed ectodermal origin in R. compacta , the Stomochord belongs to the ground pattern of the Pterobranchia and Enteropneusta. Information that would support a homology hypothesis of the chordate notochord and the hemichordate Stomochord was not found. Furthermore, there is some evidence that the Stomochord might represent a glandular organ. Thus, differences concerning the possible ontogenetic origin, morphology, and function are assumed to result from an independent evolution of the Stomochord and the notochord.

  • ultrastructure of the Stomochord and the heart glomerulus complex in rhabdopleura compacta pterobranchia phylogenetic implications
    Zoomorphology, 2003
    Co-Authors: Georg Mayer, Thomas Bartolomaeus
    Abstract:

    Pterobranchia and Enteropneusta traditionally form the highest ranking sister taxa within the Hemichordata. The most prominent feature of all representatives of the Hemichordata is the Stomochord, which is associated with an anterior excretory complex. The Stomochord has been homologized with the notochord of the Chordata species, though this hypothesis is still under debate. Recently, even the validity and position of the Pterobranchia and the Hemichordata has been doubted. These uncertainties are along with a lack of information on the Rhabdopleurida, one of the highest ranking taxa within the Pterobranchia. This study analyzes the Stomochord and the heart–glomerulus complex of Rhabdopleura compacta on the ultrastructural level. The data confirm that a glomerulus exists in representatives of the Rhabdopleurida, which previously was only known from the Cephalodiscida, the second highest ranking Pterobranchia taxon. The heart–glomerulus complex is, as expected, associated with the Stomochord. Consisting of monociliated, non-vacuolated cells that form a monolayered epithelium of presumed ectodermal origin in R. compacta, the Stomochord belongs to the ground pattern of the Pterobranchia and Enteropneusta. Information that would support a homology hypothesis of the chordate notochord and the hemichordate Stomochord was not found. Furthermore, there is some evidence that the Stomochord might represent a glandular organ. Thus, differences concerning the possible ontogenetic origin, morphology, and function are assumed to result from an independent evolution of the Stomochord and the notochord.

Georg Mayer - One of the best experts on this subject based on the ideXlab platform.

  • Ultrastructure of the Stomochord and the heart–glomerulus complex in Rhabdopleura compacta (Pterobranchia): phylogenetic implications
    Zoomorphology, 2003
    Co-Authors: Georg Mayer, Thomas Bartolomaeus
    Abstract:

    Pterobranchia and Enteropneusta traditionally form the highest ranking sister taxa within the Hemichordata. The most prominent feature of all representatives of the Hemichordata is the Stomochord, which is associated with an anterior excretory complex. The Stomochord has been homologized with the notochord of the Chordata species, though this hypothesis is still under debate. Recently, even the validity and position of the Pterobranchia and the Hemichordata has been doubted. These uncertainties are along with a lack of information on the Rhabdopleurida, one of the highest ranking taxa within the Pterobranchia. This study analyzes the Stomochord and the heart–glomerulus complex of Rhabdopleura compacta on the ultrastructural level. The data confirm that a glomerulus exists in representatives of the Rhabdopleurida, which previously was only known from the Cephalodiscida, the second highest ranking Pterobranchia taxon. The heart–glomerulus complex is, as expected, associated with the Stomochord. Consisting of monociliated, non-vacuolated cells that form a monolayered epithelium of presumed ectodermal origin in R. compacta , the Stomochord belongs to the ground pattern of the Pterobranchia and Enteropneusta. Information that would support a homology hypothesis of the chordate notochord and the hemichordate Stomochord was not found. Furthermore, there is some evidence that the Stomochord might represent a glandular organ. Thus, differences concerning the possible ontogenetic origin, morphology, and function are assumed to result from an independent evolution of the Stomochord and the notochord.

  • ultrastructure of the Stomochord and the heart glomerulus complex in rhabdopleura compacta pterobranchia phylogenetic implications
    Zoomorphology, 2003
    Co-Authors: Georg Mayer, Thomas Bartolomaeus
    Abstract:

    Pterobranchia and Enteropneusta traditionally form the highest ranking sister taxa within the Hemichordata. The most prominent feature of all representatives of the Hemichordata is the Stomochord, which is associated with an anterior excretory complex. The Stomochord has been homologized with the notochord of the Chordata species, though this hypothesis is still under debate. Recently, even the validity and position of the Pterobranchia and the Hemichordata has been doubted. These uncertainties are along with a lack of information on the Rhabdopleurida, one of the highest ranking taxa within the Pterobranchia. This study analyzes the Stomochord and the heart–glomerulus complex of Rhabdopleura compacta on the ultrastructural level. The data confirm that a glomerulus exists in representatives of the Rhabdopleurida, which previously was only known from the Cephalodiscida, the second highest ranking Pterobranchia taxon. The heart–glomerulus complex is, as expected, associated with the Stomochord. Consisting of monociliated, non-vacuolated cells that form a monolayered epithelium of presumed ectodermal origin in R. compacta, the Stomochord belongs to the ground pattern of the Pterobranchia and Enteropneusta. Information that would support a homology hypothesis of the chordate notochord and the hemichordate Stomochord was not found. Furthermore, there is some evidence that the Stomochord might represent a glandular organ. Thus, differences concerning the possible ontogenetic origin, morphology, and function are assumed to result from an independent evolution of the Stomochord and the notochord.

T.h. Bullock - One of the best experts on this subject based on the ideXlab platform.