Spatio-temporal coordination of cell cycle exit, fusion and differentiation of adult muscle precursors by Drosophila Erect wing (Ewg).

The mechanisms of cell cycle exit by myoblasts during skeletal muscle development are poorly understood. Cell cycle arrest is known to be a prerequisite for myoblast fusion and subsequent differentiation. Despite tremendous knowledge on myoblast fusion and differentiation, tissue-specific factors that spatio-temporally regulate the cell cycle exit are not well known. In this paper, we show that the transcriptional factor/co-activator "Erect wing" (Ewg) synchronises myoblast cell cycle exit with that of the fusion process. Ewg-null myoblasts show delayed temporal development of dorsal longitudinal muscles (DLMs), a group of indirect flight muscles (IFMs), which culminates to abnormal and asymmetric muscle pattern. A role for Ewg in cell cycle exit at G1/S stage is also shown. Reducing Cyclin E dose in Ewg-null mutant rescues the lack of IFMs and flight ability. Thus, we show that Ewg repression of Cyclin E expression is required for the arrest of myoblast proliferation and initiate myoblast fusion and terminal differentiation.