Evolution of the organization and function of insect homeotic complexes

In Drosophila, the Antennapedia complex (ANTC) and bithorax: complex (BXC) include homeotic (Hox) genes regulating developmental commitments in the relatively anterior and posterior portions of the embryo, respectively. The ANTC includes other developmentally significant genes as well. The beetle Tribolium has a single complex including orthologs of all of the homeotic genes and at least the non-homeotic genes zerknullt and fushi tarazu; a single complex is likely to be typical of insects in general. Available data suggest that the Tribolium complex includes large transcription units and intergenic distances important to the elaborate regulation of some Drosophila homeotic genes. Expression patterns and mutant phenotypes of homeotic genes in Tribolium indicate that if shares with Drosophila a colinearity between chromosomal order and function along the anterior-posterior axis (with one exception in common as well). However differences between Drosophila, Tribolium and some other species suggest that changes in homeotic gene function have accompanied evolution of the impressive morphological diversity displayed by insects.