作者: Mark Q Martindale , Jonathan Q Henry , None
关键词: Biology 、 Blastomere 、 Embryo 、 Mesoderm 、 Evolutionary biology 、 Anatomy 、 Bilateria 、 Endoderm 、 Cell division 、 Fate mapping 、 Body plan
摘要: Ctenophores are marine invertebrates that develop rapidly and directly into juvenile adults. They likely to be the simplest metazoans possessing definitive muscle cells possibly sister group Bilateria. All ctenophore embryos display a highly stereotyped, phylum-specific pattern of development in which every cell can identified by its lineage history. We generated fate map for Mnemiopsis leidyi injecting fluorescent tracers individual blastomeres up through 60-cell stage. The adult body plan is composed four nearly identical quadrants organized along oral-aboral axis. Each derived largely from one four-cell-stage embryo. At eight-cell stage each quadrant contains single E ("end") M ("middle") blastomere. Subsequently, micromeres formed first at aboral pole later oral pole. ctene rows, apical organ, tentacle apparatus complex structures both blastomere lineages all quadrants. born endomesodermal precursors (2M 3E macromeres). While similar, diagonally opposed share more similarities than adjacent Adult ctenophores possess two endodermal anal canals open base organ. These 2M/ macromeres. opposing macromeres unique set circumpharyngeal cells, but do not contribute canals. No other displayed such diagonal asymmetries. Clones yielded regular, completely invariant patterns descendents. Ectodermal descendents normally, always, remained within their corresponding On hand, mesodermal progeny dispersed throughout body. variability exact complements structures, with previously published deletion experiments, demonstrates interactions required normal determination. Ctenophore embryos, like those many bilaterian phyla (e.g., spiralians, nematodes, echinoids), stereotyped cleavage program some, all, determined time birth. results suggest tissues originally evolved endoderm tissue.