EVOLUTION OF EMX GENES AND BRAIN-DEVELOPMENT IN VERTEBRATES

Emx1 and Emx2 genes are known to be involved in mammalian forebrain de velopment. In order to investigate the evolution of the Emx gene famil y in vertebrates, a phylogenetic analysis was carried out on the Emx g enes sequenced in man, mice, frogs, coelacanths and zebrafish. The res ults demonstrated the existence of two clades (Emx1 and Emx2), each gr ouping one of the two genes of the investigated taxa. The only excepti on was the zebrafish Emx1-like gene which turned out to be a sister gr oup to both the Emx1 and Emx2 clusters. Such striking sequence diverge nce observed for the zebrafish Emx1-like gene could indicate that it i s not orthologous to the other Emx1 genes, and therefore, in vertebrat es there must be three Emx genes. Alternatively, if the zebrafish emx1 gene is orthologous to the tetrapod one, it must have undergone to st rong diversifying selection.