ULTRABITHORAX REGULATES GENES AT SEVERAL LEVELS OF THE WING-PATTERNING HIERARCHY TO SHAPE THE DEVELOPMENT OF THE DROSOPHILA HALTERE

Arthropods and vertebrates are constructed of many serially homologous structures whose individual patterns are regulated by Hox genes. The Hox-regulated target genes and developmental pathways that determine t he morphological differences between any homologous structures are not known. The differentiation of the Drosophila haltere from the wing th rough the action of the Ultrabithorax (Ubx) gene is a classic example of Hox regulation of serial homology, although no Ubx-regulated genes in the haltere have been identified previously. Here, we show that Ubx represses the expression of the Wingless (Wg) signaling protein and a subset of Wg- and Decapentaplegic-activated genes such as spalt-relat ed, vestigial, Serum Response Factor, and achaete-scute, whose product s regulate morphological features that differ between the wing and hal tere. In addition, we found that some genes in the same developmental pathway are independently regulated by Ubx. Our results suggest that U bx, and Hox genes in general, independently and selectively regulate g enes that act at many levels of regulatory hierarchies to shape the di fferential development of serially homologous structures.