WINGLESS IS REQUIRED FOR THE FORMATION OF A SUBSET OF MUSCLE FOUNDER CELLS DURING DROSOPHILA EMBRYOGENESIS

The final pattern of the Drosophila larval body wall muscles depends c ritically on the prior segregation of muscle founder cells. We would l ike to understand the underlying molecular mechanisms which ensure the precise allocation and placement of these muscle founder cells. We ha ve begun our analysis by examining the role of the segment polarity ge nes, known to be involved in the patterning of the ectoderm. Mutations in only one member of this class, wingless (wg), lead to the complete loss of a subset of muscle founder cells characterised by the express ion of S59. Using the GAL4-targetted expression system, we find that W ingless, a secreted glycoprotein and well characterized signalling mol ecule, acts directly on the mesoderm to ensure the formation of S59-ex pressing founder cells. Moreover, we present evidence that Wg can sign al across germ layers and that, in the wild-type embryo, Wg from the e ctoderm could constitute an inductive signal for the initiation of the development of a subset of somatic muscles.