The ryanodine receptor (RYR) genes encode evolutionarily conserved calcium release channels involved in a wide range of calcium-dependent biological processes. Here, we show that the sole Drosophila RYR gene ( dRyR ) functions in differentiated somatic and cardiac muscle as well as in developing embryonic myotubes. In the larval body wall muscles, dRyR protein localizes at the SR membranes, and dRyR knockdown adversely affects muscle contractility, suggesting its conserved role in calcium-triggered E-C coupling. After dRyR attenuation, sarcomere, and mitochondrial patterns are severely impaired, showing dRyR involvement in structural muscle properties. However, dRyR is also prominently expressed and functionally required in growing embryonic muscles. dRyR loss of function leads to myotube growth defects and thin myofiber phenotypes, while its overexpression induces myofiber splitting. Given the structural and functional conservation of dRyR , we used Drosophila to test the impact of on