STRUCTURAL-CHANGES IN THE ANTENNAPEDIA COMPLEX OF DROSOPHILA-PSEUDOOBSCURA

The discovery of the striking positional conservation between the Ante nnapedia and Bithorax homeotic gene complexes (ANT-C and BX-C) in Dros ophila melanogaster and the murine Hox and human HOX clusters has had a substantial impact on our understanding of the evolution of developm ent and its genetic regulation. Structural differences do exist among the mammalian Hox complexes and the ANT-C in D. melanogaster. To gain further insight into the evolutionary changes among these complexes, t he ANT-C was cloned in the closely related species, Drosophila pseudoo bscura. The overall structure of the ANT-C in D. pseudoobscura is high ly similar to its D. melanogaster counterpart; however, two difference s in the organization of the ANT-C have been identified. First, the z2 gene, a member of the ANT-C in D. melanogaster, is not present in the D. pseudoobscura ANT-C and is possibly absent from the D. pseudoobscu ra genome. Second, the orientation of the Deformed gene is inverted in D. pseudoobscura, providing it with a 5' to 3' direction of transcrip tion identical to the remaining ANT-C homeobox genes with the exceptio n of fushi tarazu. These differences demonstrate that subtle changes c an occur in ANT-C structure during relatively short periods of evoluti onary divergence, although the fundamental organization of the complex is conserved. These observations and others suggest that the complex is not absolutely rigid but that selective pressures have maintained t his organization of genes for some functional reason that remains elus ive.