Understanding the genetic mechanisms that control brain patterning in verte
brates represents a major challenge for developmental neurobiology. The clo
ning of genes likely to be involved in the organization of the brain and an
analysis of their roles have revealed insights into the molecular pathways
leading to neural induction, tissue specification, and regionalization of
the brain. Among these genes, both Otx1 and Otx2, two murine homologs of th
e Drosophila orthodenticle (otd) gene, contribute to several steps in brain
morphogenesis. Recent findings have demonstrated that Otx2 plays a major r
ole in gastrulation and in the early specification of the anterior neural p
late while Otx1 is mainly involved in corticogenesis, and Otx1 and Otx2 gen
es cooperate in such a way that a minimal level of OTX proteins are require
d for proper regionalization and subsequent patterning of the developing br
ain. Finally, experiments have shown functional equivalence between Drosoph
ila otd and vertebrate Otx genes, suggesting a surprising conservation of f
unction required in brain development throughout evolution.