FUNCTIONAL-ANALYSIS OF THE MOUSE HOMEOBOX GENE HOXB9 IN DROSOPHILA DEVELOPMENT

Mammalian genomes contain clusters of homeobox genes (Hox-C, HOX-C) wh ich are structurally similar to the homeotic genes of the Drosophila H OM complex. One method for assessing the functional similarity of part icular Drosophila HOM and mammalian Hox genes is to test the ability o f Hox genes to induce homeotic phenotypes when expressed in developing Drosophila. Here we describe such functional tests using mouse HoxB9 (formerly Hox-2.5), whose closest structural relative in Drosophila is Abdominal-B. When expressed from a heat shock promoter, HoxB9 induces transformations of head towards more posterior identities in Drosophi la larvae and adults. These transformations share some similarities wi th the phenotypic effects produced by ectopically expressed Abdominal- B, but are also similar to the transformations induced by Antennapedia and mouse HoxB6 (Hox-2.2), suggesting that HoxB9 specifies a position al identity that is intermediate between Antennapedia and Abdominal-B.