FUSION FROM MYOBLASTS TO MYOTUBES IS DEPENDENT ON THE ROLLING STONE GENE (ROST) OF DROSOPHILA

The development and differentiation of the body wall musculature in Dr osophila are accompanied by changes in gene expression and cellular ar chitecture, We isolated a Drosophila gene, termed rolling stolae (rest ), which, when mutated, specifically blocks the fusion of mononucleate d cells to myotubes in the body wall musculature. beta 3 tubulin, whic h is an early marker for the onset of mesoderm differentiation, is sti ll expressed in these cells, Gastrulation and mesoderm formation, as w ell as the development of the epidermis and of the central and periphe ral nervous systems, appear quite normal in homozygous rolling stone e mbryos. Embryonic development stops shortly before hatching in a P-ele ment-induced mutant, as well as in 16 EMS-induced alleles, In mutant e mbryos, other mesodermal derivatives such as the visceral mesoderm and the dorsal vessel, develop fairly normally and defects are restricted to the body wall musculature, Myoblasts remain as single mononucleate d cells, which express muscle myosin, showing that the developmental p rogram of gene expression proceeds, These myoblasts occur at positions corresponding to the locations of dorsal, ventral and pleural muscles , showing that the gene rolling stone is involved in cell fusion, a pr ocess that is independent of cell migration in these mutants, This gen etic analysis has set the stage for a molecular analysis to clarify wh ere the rolling stone action is manifested in the fusion process and t hus gives insight into the complex regulating network controlling the differentiation of the body wall musculature.