Region-specific expression of the helix-loop-helix gene BETA3 in developing and adult brains

Members of the basic helix-loop-helix (bHLH) transcription factor family are crucial regulators of neuronal cell generation and cell fate. A number of bHLH genes are expressed in the developing cerebral cortex, including MASH-1, neurogenin2 and NeuroD implying the existence of a regulatory and possibly redundant network of family members. BETA3 is a novel member originally cloned from pancreatic cells but we report here highly restricted expression patterns in developing forebrain structures that are highly stage-specific. We show that BETA3 mRNA is found in both neocortex and archicortex, mainly in cells that have reached their migratory destinations but is largely absent from proliferative zones. These expression data would suggest that BETA3 function is linked to the establishment rather than the initiation of neuronal fates.