Figure 3. Transcription factors in the VZ establish an area identity fate map.

(a) Arealization of the cerebral cortex is initiated by diffusible morphogens and signaling molecules secreted from opposing sides of the neocortical periphery (left panel). These signals induce expression of complementary and orthogonal transcription factor gradients such as Pax6/Emx2 and Sp8/Couptf1, seen in a schematized flatmount view of the ventricular zone (VZ) (b) Pax6 is expressed most highly rostrolaterally, in opposition to Emx2, which is expressed most highly caudomedially. Similarly, Sp8 is expressed most highly rostromedially, in opposition to Couptf1, which is expressed most highly caudolaterally. Gradients are shown in wholemount (left) and sagittal (right) views for each. (c) Progenitors located at different medio-lateral and rostro-caudal coordinates express specific levels of these transcription factors, which combinatorially establish a fate map of cortical areas in the ventricular zone. This fate map is later translated into a definitive area map in the cortical plate (CP), shown in flatmount view (left panel). Manipulation of morphogen signaling or VZ transcription factor expression results in dramatic changes in the size and position of cortical areas (right panel). Hatching indicates mixed area identity.

A1, primary auditory cortex; Ep, electroporation; M1, primary motor cortex; S1, primary somatosensory cortex; sey/sey, small eye hypomorphic mutant; V1, primary visual cortex; YAC, yeast artificial chromosome