The Drosophila Him gene is essential for adult muscle function and muscle stem cell maintenance

Muscle stem cells (MuSCs), or "satellite cells," are vital for vertebrate muscle growth, homeostasis, and repair. The discovery of analogous cells in Drosophila opens experimental opportunities in this genetically tractable model. Here, we show that the myogenic inhibitor gene Him, as well as being expressed in the myoblasts that form the flight and jump muscles, is expressed in flight muscle MuSCs. This makes Him only the second marker of these insect adult MuSCs. Furthermore, Him mutants exhibit disrupted jump muscle organization, impaired jumping ability, and a reduced pool of flight muscle myoblasts. In the flight muscles themselves, Him mutants show an age-dependent decrease in MuSC number, indicating Him is required for MuSC maintenance. This decrease coincides with reduced flight performance. Thus, Him is a new marker of Drosophila adult MuSCs and is the first gene shown to be required as flies age to maintain both MuSC number and flight ability.