Negative regulation of dorsoventral signaling by the homeotic gene Ultrabithorax during haltere development in Drosophila

Growth and patterning during Drosophila wing development are mediated by si gnaling from its dorsoventral (D/V) organizer. In the metathorax, wing deve lopment is essentially suppressed by the homeotic selector gene Ultrabithor ax (Ubx) to mediate development of a pair of tiny balancing organs, the hal teres. Here we show that expression of Ubx in the haltere D/V boundary down -regulates its D/V organizer signaling compared to that of the wing D/V bou ndary. Somatic loss of Ubx from the haltere D/V boundary thus results in th e formation of a wing-type D/V organizer in the haltere held. Long-distance signaling from this organizer was analyzed by assaying the ability of a Ub x(-) clone induced in the haltere D/V boundary to effect homeotic transform ation of capitellum cells away from the boundary. The clonally restored win g D/V organizer in mosaic halteres not only enhanced the homeotic transform ation of Ubx(-) cells in the capitellum but also caused homeotic transforma tion of even Ubx(+) cells in a genetic background known to induce excessive cell proliferation in the imaginal discs. In addition to demonstrating a n on-cell-autonomous role for Ubx during haltere development, these results r eveal distinct spatial roles of Ubx during maintenance of cell fate and pat terning in the halteres. (C) 1999 Academic Press.