Characterisation of a Mutation that Disrupts Myoblast Fusion during Drosophila Embryonic Myogenesis. S.D. Menon , S. Bahri , W. Chia. Inst of Molecular & Cell Biol, National Univ Singapore, Singapore 117609, Republic of Singapore.

   A key step in the genesis of the larval somatic musculature is the fusion between specialised myoblasts called muscle founders and surrounding 'naive' myoblasts. We have isolated a recessive lethal mutation that disrupts this process. Analyses using several muscle founder markers including Eve and Kruppel indicate that the mutation does not perturb events leading to the specification of founder cells. This point is further supported by the observation that at stage 16, mutant embryos lack muscle fibres but nevertheless have almost all of the 30 abdominal muscles represented by a mono- or occasionally bi-nucleated innervated cell attached at the respective muscle position. All myoblasts express muscle myosin heavy chain and tubulin and aggregate in dorsal, lateral and ventral muscle-forming areas, suggesting that this mutation uncouples differentiation leading to myoblast fusion from other aspects of myoblast differentiation. We have mapped the mutation to the 68EF region of the third chromosome and will present data on the transcripts isolated.