Fig. 9. Schematic presentation of a role of Fez and Fezl in diencephalon patterning. Fez and Fezl are expressed in the telencephalon and rostral diencephalon (prospective prethalamus) and function to suppress the formation of the caudal diencephalon, which expresses Irx1 and Wnt3a. In the absence of Fez and Fezl, the rostral diencephalon does not form and instead caudal diencephalon expands rostrally at E9.5. Subsequently at E10.5, the prethalmaus and the ZLI, which is normally located in the interface between the prethalamus and thalamus, do not form in Fez^-/-Fezl^-/- embryos. The caudal diencephalon, including the thalamus and pretectum, is expanded in Fez^-/-Fezl^-/- embryos. The formation of thalamus, however, is dependent on inductive signals (e.g. Shh) from the ZLI. In Fez^-/-Fezl^-/- embryos, the thalamus does not grow properly, but the anterior pretectum remains expanded at E12.5. apt, anterior pretectum; di, diencephalon; pth, prethalamus, ppt, posterior pretectum; tel, telencephalon; th, thalamus.