What are the targets of FGF signaling in the neocortex?
A common theme in developmental biology is the role of signaling centers that secrete diffusible molecules and influence the fate of the recipient tissues. The developing neocortex is subject to the patterning effects of many diffusible signal proteins such as bone morphogenetic proteins (BMPs), Wnt family proteins, FGFs and Hedgehog-related proteins (see Figure 1c) (for reviews see [4,12]). Genetic gain- and loss-of-function studies implicate FGF8 as the primary secreted factor that imparts positional information on the rostro-caudal axis of the developing neocortex [4,13,14]. To assess the contribution of FGF signaling, Sansom et al. [5] took advantage of a mouse with a foxg1-driven forebrain-specific mutation in the FGF receptor 1 (Fgfr1); the phenotype of this mutant mouse is consistent with an abrogation of FGF8-mediated patterning in the neocortical area [15,16]. Careful comparison (nine replicates at E12.5) of the whole neocortex between the Fgfr1-mutant line and the foxg1-drive
