CONVERSION OF A MESODERMALIZING MOLECULE, THE XENOPUS BRACHYURY GENE,INTO A NEURALIZING FACTOR

It has been shown previously that a Xenopus homolog of the mouse gene Brachyury, Xbra, can initiate mesodermal differentiation. Here, I repo rt that a Xbra mutant truncated at the carboxyl terminus, B304, has lo st the mesodermalizing activity and can block the activity of the wild -type Xbra. Injection of B304 mRNA led to formation of neural structur es in animal cap explants. Examination of molecular markers in B304-in jected explants shows expression of anterior neural markers in the abs ence of mesodermal markers, indicating that B304 can cause neuralizati on without the mediation of mesoderm. Implications of these findings o n intracellular mechanisms underlying the initiation of neural differe ntiation in the ectodermal cells are discussed.