Fig. 4.

A host of signals act in concert to confer anterior forebrain identity. Signals such as WNTs, FGFs, and BMPs exert a posteriorizing action on the neural plate (blue arrows). Counteracting activation of the respective pathways in the anterior forebrain, secreted inhibitors such as Cerberus, Lefty1, Dkk1, Noggin, and Chordin (red arrows) are released by the underlying AVE, ADE, and prechordal plate. Within the prospective anterior forebrain, intrinsic factors such as HESX1, SIX3, and TCF3, aid in regulating the competence of neural tissue to not respond to posteriorizing signals, possibly by preventing the expression of target genes of these pathways, hence maintaining anterior forebrain identity. AF anterior forebrain, PF posterior forebrain, MB midbrain, HB hindbrain, SC spinal cord, AVE anterior visceral endoderm, ADE anterior definitive endoderm, pp prechordal plate