Emx and Nfi Genes Regulate Cortical Development and Axon Guidance in the Telencephalon

The Emx and Nuclear Factor One (Nfi) genes encode transcription factors that regulate numerous embryonic developmental processes. The two mammalian Emx genes, Emx1 and Emx2, are expressed in the embryonic cortex and regulate the specification of the cortex into different sensory and motor areas along the rostrocaudal axis. To date, few developmental processes have been attributed specifically to Emx1, with most analyses demonstrating a redundancy of function between Emx1 and Emx2, with Emx2 being most essential for development. Here we provide evidence that Emx1 and Emx2 regulate different developmental processes during corpus callosum formation and review how both genes function in cellular migration and the formation of cortical axon projections. The Nfi gene family is made up of four members, Nfia, Nfib, Nfic and Nfix. Expression analyses show that Nfia, Nfib and Nfix are expressed in the developing telencephalon. They play roles in patterning, glial development, cortical cell migration and axon guidance. We review the role of these genes in cortical cell migration, glial development and the formation of cortical axon projections, and examine the overlapping mutant phenotypes between the Emx and Nfi gene families.