Otx and Emx homeobox genes in brain development.

Over the last few years great progress has been made in the understanding of the formation and regionalisation of the mouse brain. In this review we will focus our attention on two families of homeobox-containing genes essentially coding for four transcription factors involved in brain and forebrain development: the two Emx and the two Otx genes. Here we describe the expression pattern of these genes in the developing mouse, as well as the characterisation of the corresponding knockout mice with special emphasis on Emx2. Whereas Otx genes are clearly involved in the formation and regionalisation of the whole rostral brain, comprised of forebrain and midbrain, our data suggest a role for Emx2 in the specification of the cytoarchitecture of the cerebral cortex, achieved through the control of proliferation of neuronal precursors and of migration of newly-formed neurons to their final destination.