Action of the Brachyury gene in mouse embryogenesis.

The murine developmental mutation T identifies a gene required in mesoderm formation. T/T mutant embryos develop normally to the primitive streak stage; during early organogenesis they show insufficient mesoderm and absence of the notochord. The mutants die at around 10 days of gestation because of the lack of the allantois. We have localized the T mutation relative to DNA markers and used a combination of genetic and molecular techniques to clone the T gene. Expression of the T gene is restricted to nascent mesoderm and to the notochord, the tissues most strongly affected by the mutation. Recent results suggest that the T gene encodes a nuclear factor involved in establishing notochord cell identity and differentiation, and is directly or indirectly involved in the organization of axial development.