Complex signaling responsible for molecular regionalization of the cerebral cortex

The formation of discrete functional areas is a key event in the development of the cerebral cortex. The expression patterns of several molecules associated with axon guidance reveal specification of regional identity during fetal development within the cortex, with different area-specific features acquired at very early to later stages of corticogenesis. Cell culture experiments suggest that complex mechanisms regulate the differentiation of region-appropriate phenotypes. In all instances that we have examined thus far, however, the final phenotype adopted by cortical neurons is governed by the capacity of the cell to respond to regionalizing signals; this is reflected in the heterogeneity of receptor expression by progenitors, and the temporal and spatial distribution of such signals within the forebrain.