Gerhart John, Lowe Christopher, Kirschner Marc
Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-3200, USA.
Curr Opin Genet Dev. 2005 Aug;15(4):461-7. doi: 10.1016/j.gde.2005.06.004.
Hemichordates, the phylum of bilateral animals most closely related to chordates, could reveal the evolutionary origins of chordate traits such as the nerve cord, notochord, gill slits and tail. The anteroposterior maps of gene expression domains for 38 genes of chordate neural patterning are highly similar for hemichordates and chordates, even though hemichordates have a diffuse nerve-net. About 40% of the domains are not present in protostome maps. We propose that this map, the gill slits and the tail date to the deuterostome ancestor. The map of dorsoventral expression domains, centered on a Bmp-Chordin axis, differs between the two groups; hemichordates resemble protostomes more than they do chordates. The dorsoventral axis might have undergone extensive modification in the chordate line, including centralization of the nervous system, segregation of epidermis, derivation of the notochord, and an inversion of organization.
半索动物门是与脊索动物关系最为密切的双侧对称动物门，它可能揭示脊索动物特征（如神经索、脊索、鳃裂和尾巴）的进化起源。尽管半索动物具有弥散的神经网，但半索动物和脊索动物中38个参与脊索动物神经模式形成的基因的前后表达域图谱高度相似。约40%的表达域在原口动物图谱中不存在。我们认为，这种图谱、鳃裂和尾巴可追溯到后口动物祖先。以Bmp - Chordin轴为中心的背腹表达域图谱在这两组动物中有所不同；半索动物与原口动物的相似性超过与脊索动物的相似性。背腹轴可能在脊索动物谱系中经历了广泛的修饰，包括神经系统的集中化、表皮的分离、脊索的衍生以及组织结构的反转。
