Characterization of the Hox gene cluster in the malaria vector mosquito, Anopheles gambiae

The Hox genes play a central role in regulating development and are involved in the specification of cell fates along the anteroposterior axis. In insects and vertebrates, these genes are clustered and organized in an arrangement that is largely conserved across evolutionary lineages. By exploiting the sequence conservation of the homeobox, orthologues of the Hox genes Sex combs reduced (Scr), fushi tarazu (ftz), Antennapedia (Antp), Ultrabithorax (Ubx), and abdominal-A (abd-A) have been isolated from the malaria vector mosquito, Anopheles gambiae. These genes were first identified in Drosophila, where they achieve a high level of functional complexity, in part, by the use of alternative promoters, polyadenylation sites, and splicing to generate different protein isoforms. Preliminary analyses of the Anopheles Hox genes suggest that they do not achieve their functional complexity in the same manner. Using a combination of in situ hybridization to polytene chromosomes and chromosome walking, the Anopheles Hox genes have been localized to a single cluster in the region 19D-E on chromosome 2R, a situation distinct from that of Drosophila where the Hox complex is split into two clusters. This study, therefore, provides a framework for future comparative analyses of the structure, organization, and expression of developmental regulatory genes between the lower and higher Diptera. Moreover, the genes that have been isolated enhance the genetic and physical maps of chromosome 2R in this medically important mosquito species.