| Research Abstract |
I have investigated several cDNA clones, which encode for ventralizing agents. Among these factors, the roles of msx-1 and msx-2 in the dorsoventral axis formation have been extensively analyzed. These transcriptional repressor proteins were expressed in presumptive ectoderm and mesoderm ventrally, but not dorsally, at gastrula stage. Both msx-1 and msx-2 possessed a similar ventralizing activity, but that of msx-2 was higher than of msx-1, as revealed by the injection of RNA into dorsal blastomeres. The secondary axis induced by the injection of tBR was rescued by simultaneous injection of msx-1/msx-2. Furthermore, if VP-16/msx-1 fusion RNA, which was expected to function as a dominant negative msx-1, was injected into the ventral blastomeres, partial Secondary axis was formed. Therefore, msx-1 and msx-2 transduce a main tract of BMP-4 signaling. Msx factors also have a role in neural tissue induction in ectodermal cells. If msx-1 was coinjected with neural inducer genes such as noggin or cerberus, the expression of N-CAM was completely suppressed. As also shown in tBR (which directly induces neural tissue in animal cap), VP 16/msx-1 fusion RNA was able to induce neural tissue directly in animal cap cells. The results indicate that msx proteins play a central role in establishing dorso-ventral axis and in neural tissue formation in gastrulating embryo, by antagonizing the expression of organizer genes. The expression and function of GATA-1 (another transcriptional regulator) and BMP-1 (metalloprotease) in Xenopus embryo have been also investigated in this study.
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