Generating the cerebral cortical area map.

The view that the cortical primordium is initially patterned in similar ways to the rest of the embryo has been a conceptual breakthrough. We now have a new starting point for understanding how the cortical area map is established and how maps may change and evolve. Here we review findings that signaling molecules secreted from distinct cortical signaling centers establish positional information in the cortical primordium and regulate regional growth. In other embryonic systems, positional signals would regulate the patterned expression of transcription factors, leading, in a gene regulatory cascade, to the patterned differentiation of the tissue. We discuss candidate transcription factors with respect to such a model of cortical patterning. Finally, embryonic structures interact to pattern one another. We review data suggesting that the thalamus and cortex are patterned independently then interact to generate the final cortical area map.