Emx1, Emx2 and Pax6 in specification, regionalization and arealization of the cerebral cortex

Three basic aspects of cerebral cortex development — specification of cortical versus ganglionic identity, regionalization of the early cortical primordium and arealization of the developing cortex — were the main subject of our recent investigations. We previously demonstrated that the two homeobox genes Emx2 and Pax6 promote development of caudal–medial and rostral–lateral cortex, respect- ively, by properly shaping the early cortical protomap and possibly modulating the tangential growth ratio between medial and lateral cortical anlagen. More recently, by analyzing the brains of embryos bearing mutations for Emx2 and Pax6 in different combinations, we found that both genes are necessary and sufficient for a more basic developmental choice, i.e. the specification of neuroblasts in the dorsal telencephalon as cortical versus ganglionic neuroblasts. Finally, we explored the possible roles of the Emx2 paralog, Emx1, in these processes. By looking at embryos mutant for Emx1, Emx2 and Pax6 in various combinations, we did not get any evidence of Emx1 involvement in the process of cortical specification; conversely, this gene appeared to be involved to some extent in the process of regionalization of the cortical primordium along the medial–lateral axis, as a promoter of medial fates.