Regulation of area identity in the mammalian neocortex by Emx2 and Pax6

The contribution of extrinsic and genetic mechanisms in determining areas o f the mammalian neocortex has been a contested issue. This study analyzes t he roles of the regulatory genes Emx2 and Pax6, which are expressed in oppo sing gradients in the neocortical ventricular zone, in specifying areas. Ch anges in the patterning of molecular markers and area-specific connections between the colter and thalamus suggest that arealization of the neocortex is disproportionately altered in Emx2 and Pax6 mutant mice in opposing mann ers predicted from their countergradients of expression: rostral areas expa nd and caudal areas contract in Emx2 mutants, whereas the opposite effect i s seen in Pax6 mutants. These findings suggest that Emx2 and Pax6 cooperate to regulate arealization of the neocortex and to confer area identity to c ortical cells.