T-BRAIN-1 - A HOMOLOG OF BRACHYURY WHOSE EXPRESSION DEFINES MOLECULARLY DISTINCT DOMAINS WITHIN THE CEREBRAL-CORTEX

The mechanisms that regulate regional specification and evolution of t he cerebral cortex are obscure. To this end, we have identified and ch aracterized a novel murine and human gene encoding a putative transcri ption factor related to the Brachyury (T) gene that is expressed only in postmitotic cells. T-brain-1 (Tbr-1) mRNA, is largely restricted to the cerebral cortex, where during embryogenesis it distinguishes doma ins that we propose may give rise to paleocortex, limbic cortex, and n eocortex. Tbr-1 and Id-2 expression in the neocortex have discontinuit ies that define molecularly distinct neocortical areas. Tbr-1 expressi on is analyzed in the context of the prosomeric model. Topological map s are proposed for the organization of the dorsal telencephalon.