Diversification of arthropod Hox genes as a paradigm for the evolution of gene functions

Hox genes are highly conserved throughout the metazoans in both sequence, chromosomal arrangement, and function. Yet within the arthropods these genes have undergone considerable diversification. We examine ancestral and novel functions of arthropod Hox genes in an attempt to understand how these functions might evolve. We suggest that functional diversification of Hox genes begins with the acquisition of multiple distinct cis-regulatory elements responsible for different aspects of their gene expression. Gene duplication may serve to dissociate the functional-selective constraints associated with each of these regulatory elements and to allow divergence of the corresponding coding sequences.