Otx1 and Otx2 in the development and evolution of the mammalian brain

In the last decade, a number of genes related to the induction, specification and regionalization of the brain were isolated and their functional properties currently are being dissected. Among these, Otx1 and Otx2 play a pivotal role in several processes of brain morphogenesis. Findings from several groups now confirm the importance of Otx2 in the early specification of neuroectoderm destined to become fore-midbrain, the existence of an Otx gene dosage-dependent mechanism in patterning the developing brain, and the involvement of Otx1 in corticogenesis. Some of these properties appear particularly fascinating when considered in evolutionary terms and highlight the central role of Otx genes in the establishment of the genetic program defining the complexity of a vertebrate brain. This review deals with the major aspects related to the roles played by Otx1 and Otx2 in the development and evolution of the mammalian brain.