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HpEts implicated in primary mesenchyme cell differentiation of the sea urchin (Hemicentrotus pulcherrimus) embryo

Published online by Cambridge University Press:  16 July 2018

Daisuke Kurokawa
Affiliation:
Laboratory of Molecular Genetics, Graduate Department of Gene Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima 739, Japan
Takashi Kitajima
Affiliation:
Department of Biology, Tokyo Metropolitan University, Minami-Ohsawa, Hachioji, Tokyo 192-03, Japan
Keiko Mitsunaga-Nakatsubo
Affiliation:
Laboratory of Molecular Genetics, Graduate Department of Gene Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima 739, Japan
Shonan Amemiya
Affiliation:
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113, Japan
Hiraku Shimada
Affiliation:
Laboratory of Molecular Genetics, Graduate Department of Gene Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima 739, Japan
Koji Akasaka
Affiliation:
Laboratory of Molecular Genetics, Graduate Department of Gene Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima 739, Japan

Extract

In sea urchin embryogenesis it has been suggested that the initial territories are specified by a combination of the asymmetric distribution of cytoplasmic determinants and cell-cell interactions. At the 60-cell stage blastomeres clonally originated from founder cells divide the embryo into five distinct territories: small micromeres, large micromeres, vegetal plate, oral ectoderm and aboral ectoderm. The territories are identified by the expression of specific marker genes and their cell lineages (Davidson, 1989, 1991). The large micromeres are thought to play a role as an organiser and initiate a cascade of signal transduction toward overlying cells (Davidson, 1989). In this model the large micromeres induce the overlying veg2 tier, specifying the vegetal plate (Ransick & Davidson, 1993, 1995). The veg2 tier then induces the overlying cells, which include gut cells and cells of the prospective ectodermal territories (Wikramanayake et al., 1995; Wikramanayake & Klein, 1997). Thus, the large micromeres, which are the prospective primary mesenchyme cells (PMCs), play a key role in cell fate specification and axis determination during sea urchin embryogenesis. Previous data suggested that the large micromeres are autonomously specified to become PMCs by maternally inherited determinants (Okazaki, 1975; Kitajima & Okazaki, 1980). An important question in sea urchins embryogenesis is the identity and function of the proposed maternal determinants.

Type
Special Lecture for Citizens
Copyright
Copyright © Cambridge University Press 1999

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References

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