The specific aim of this proposal is to study the mechanisms by which regional and functional differences are established in the vertebrate forebrain during development. Using chick as a model, we will identify genetic fate determinants in the forebrain by examining the normal spatio-temporal expression of candidate genes. Possible new candidate genes such as vertebrate homologues of the drosophila distal-less homeobox gene (Dlx family), known to play a role in the specification of anterior segments, will be cloned using a PCR based approach. To study their role in forebrain patterning, we will use replication competent retroviral vectors to target over-expression of these genes in the developping chick brain. By analysing the effect these experiments have on the expression of specific markers, we will explore the hierarchy of genetic interactions that control the process of regionalisation in the forebrain.