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Published September 1998 | Published
Journal Article Open

Specification of cell fate in the sea urchin embryo: summary and some proposed mechanisms


An early set of blastomere specifications occurs during cleavage in the sea urchin embryo, the result of both conditional and autonomous processes, as proposed in the model for this embryo set forth in 1989. Recant experimental results have greatly illuminated the mechanisms of specification in some early embryonic territories, though others remain obscure. We review the progressive process of specification within given lineage elements, and with reference to the early axial organization of the embryo. Evidence for the conditional specification of the veg(2) lineage subelement of the endoderm and other potential interblastomere signaling interactions in the cleavage-stage embryo are summarized. Definitive boundaries between mesoderm and endoderm territories of complex. the vegetal plate, and between endoderm and overlying ectoderm, are not established until later in development. These processes have been clarified by numerous observations on spatial expression of various genes, and by elegant lineage labeling studies. The early specification events depend on regional mobilization of regulatory factors resulting at once in the zygotic expression of genes encoding transcription factors, as well as downstream genes encoding proteins characteristic of the cell types that will much later arise from the progeny of the specified blastomeres. This embryo displays a maximal form of indirect development. The gene regulatory network underlying the embryonic development reflects the relative simplicity of the completed larva and of the processes required for its formation. The requirements for postembryonic adult body plan formation in the larval rudiment include engagement of a new level of genetic regulatory apparatus, exemplified by the Hox gene complex.

Additional Information

© The Company of Biologists Limited 1998. Accepted 12 June; published on WWW 6 August 1998. We are extremely grateful to reviewers of drafts of this manuscript for their perspicacious and informed critical assistance. Its present form owes much to their contributions. These were Drs Lynne and Robert Angerer of the University of Rochester, Drs. Ellen Rothenberg and Paola Oliveri of this Institute, and Dr James W. Posakony of UCSD. This effort was supported by NIH grant (HD-05753) to EHD and by NSF grant (IBN9604454) to RAC.

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August 22, 2023
August 22, 2023