Evolutionary conservation and conversion of Foxg1 function in brain development

Among the forkhead box protein family, Foxg1 is a unique transcription factor that plays pleiotropic and non-redundant roles in vertebrate brain development. The emergence of the telencephalon at the rostral end of the neural tube and its subsequent expansion that is mediated by Foxg1 was a key reason for the vertebrate brain to acquire higher order information processing, where Foxg1 is repetitively used in the sequential events of telencephalic development to control multi-steps of brain circuit formation ranging from cell cycle control to neuronal differentiation in a clade- and species-specific manner. The objective of this review is to discuss how the evolutionary changes in cis- and trans-regulatory network that is mediated by a single transcription factor has contributed to determining the fundamental vertebrate brain structure and its divergent roles in instructing species-specific neuronal circuitry and functional specialization.