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Binary specification of nerve cord and notochord cell fates in ascidian embryos

Minokawa, Takuya and Yagi, Kasumi and Makabe, Kazuhiro W. and Nishida, Hiroki (2001) Binary specification of nerve cord and notochord cell fates in ascidian embryos. Development, 128 (11). pp. 2007-2017. ISSN 0950-1991.

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In the ascidian embryo, the nerve cord and notochord of the tail of tadpole larvae originate from the precursor blastomeres for both tissues in the 32-cell-stage embryo. Each fate is separated into two daughter blastomeres at the next cleavage. We have examined mechanisms that are responsible for nerve cord and notochord specification through experiments involving blastomere isolation, cell dissociation, and treatment with basic fibroblast growth factor (bFGF) and inhibitors for the mitogen-activated protein kinase (MAPK) cascade. It has been shown that inductive cell interaction at the 32-cell stage is required for notochord formation. Our results show that the nerve cord fate is determined autonomously without any cell interaction. Presumptive notochord blastomeres also assume a nerve cord fate when they are isolated before induction is completed. By contrast, not only presumptive notochord blastomeres but also presumptive nerve cord blastomeres forsake their default nerve cord fate and choose the notochord fate when they are treated with bFGF. When the FGF-Ras-MAPK signaling cascade is inhibited, both blastomeres choose the default nerve cord pathway, supporting the results of blastomere isolation. Thus, binary choice of alternative fates and asymmetric division are involved in this nerve cord/notochord fate determination system, mediated by FGF signaling.

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Additional Information:© 2001 The Company of Biologists Limited. Accepted March 19, 2001. We thank the staff of the Asamushi Marine Biological Station and the Otsuchi Marine Research Center for their help in collecting live ascidians, and the staff of the Misaki Marine Biological Station for their help in maintaining them. We are also grateful to our colleagues, especially Dr T. Nishikata for providing monoclonal antibody 5F1D5, Dr T. Miya for providing plasmid containing HrTBB2 cDNA, instruction on in situ hybridization and valuable discussion, and Mr S. Darras and Dr P. Lemaire for valuable discussion and suggestion. This work was supported by the Research for the Future program from the Japanese Society for the Promotion of Science (96L00404) and a grant from the HFSP organization (RG-0299/98).
Funding AgencyGrant Number
Japanese Society for the Promotion of Science96L00404
Human Frontier Science ProgramRG-0299/98
Subject Keywords:Ascidian embryogenesis, Nerve cord, Notochord, Developmental fate, Autonomous differentiation, Induction, Default fate
Issue or Number:11
Record Number:CaltechAUTHORS:MINdev01
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12900
Deposited By: Archive Administrator
Deposited On:09 Jan 2009 08:00
Last Modified:03 Oct 2019 00:32

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