Control of tissue morphogenesis by the HOX gene .

Mutations in the () gene cause homeotic transformation of the normally two-winged into a four-winged mutant fly. encodes a HOX family transcription factor that specifies segment identity, including transformation of the second set of wings into rudimentary halteres. is known to control the expression of many genes that regulate tissue growth and patterning, but how it regulates tissue morphogenesis to reshape the wing into a haltere is still unclear. Here, we show that acts by repressing the expression of two genes in the haltere, and , both of which encode transmembrane proteases that remodel the apical extracellular matrix to promote wing morphogenesis. In addition, induces expression of the in the haltere, which prevents the basal extracellular matrix remodelling necessary for wing morphogenesis. Our results provide a long-awaited explanation for how Ubx controls morphogenetic transformation.