MOLECULAR EVOLUTION OF THE BRAIN OF CHORDATES

The molecular basis of regionalisation and patterning of the developin g brain is an area of current intense interest. Members of the Otx, Pa x-2/5/8 and Hox gene families appear to play important roles in these processes in vertebrates, but functional divergence and genetic redund ancy arising from gene duplication events obscures our view of the rol es played by these genes during the evolution of vertebrate brains, De termination of the ancestral gene copy number in chordates through mol ecular phylogenetics, accompanied by gene expression analysis in all t hree chordate subphyla (vertebrates, cephalochordates and urochordates ) may distinguish between ancestral and derived expression domains and give clues to the roles played by these genes in chordate ancestors. Application of this comparative approach indicates evolutionary homolo gous brain regions (fore-/midbrain, isthmus/cerebellum and hindbrain) in chordates and supports homology of the frontal eye of cephalochorda tes to the paired eyes of vertebrates.