[Hox genes, developmental evolution and the origin of vertebrates].

Homeobox genes comprise a diverse multigene family encoding transcription factors, many of which are key control genes in early development. The roles of several homeobox gene subfamilies have been widely conserved through animal evolution, but there are detailed differences in homeobox gene number, genomic organisation and gene expression between taxa. We have compared Hox and other homebox genes between vertebrates and their closest living relatives, Amphioxus. The results suggest that after evolutionary divergence of these two lineages, homeobox and other genes were duplicated in the lineage leading to vertebrates, but that Amphioxus retained the archetypal homeobox gene organisation. We suggest that prior to vertebrate origins there was an intense phase of gene duplication, followed by recruitment of new developmental control genes to new roles. These genetic changes may have permitted the evolution of novel developmental and anatomical characters, and the origin of vertebrates.