The winged-helix transcriptional repressor (WH) BF-1 gene encodes brain factor 1 (BF-1), also known as foxg1, and is essential for the proliferation of progenitor cells in the cerebral cortex and influences regional patterning in the mammalian telencephalon (14). WH proteins are a family of putative transcriptional regulators with diverse roles in development, and are characterized by a highly conserved DNA binding structure, the WH domain (1,5,6). BF-1 plays a critical role in the development of the cerebral hemispheres of the brain and targeted disruption of the gene leads to severe defects in the development of telencephalic structures, such as the cerebral cortex and basal ganglia (1). The loss of BF-1 results in an accelerated rate of neuronal differentiation and the shortening of the neurogenetic period in the embryonic cerebral cortex (1,7). BF-1 is expressed by E8.5 in telencephalic progenitors (1). It may also regulate the response of cerebral cortical progenitors to environmental cues (1).