Figure 4.

The outline of a cellular network for controlling neocortical area formation. FGF8, signaling through FGF receptors, induces or increases expression of the rostrally expressed transcription factors, the ETS factors Pax6 and FGF8. Sp8 in turn increases expression of Fgf8 rostrally. The rostral and caudal transcription factors show a degree of mutual cross-repression. Among the caudal transcription factors, COUP-TFI appears to be upstream of Emx2, as loss of Emx2 does not alter COUP-TFI expression, and COUP-TFI-null cortices have a more severe patterning phenotype than that observed in Emx2 nulls.