Dystrophin interacts with Msp300 to regulate myonuclear positioning and microtubule organization

In Drosophila myogenesis, myonuclei are actively moved during embryogenesis, and their spacing is maintained through an anchoring mechanism in the fully differentiated myofiber. Although we have identified microtubule-associated proteins, motors and nuclear envelope proteins that regulate myonuclear spacing, the developmental time during which each gene functions has not been tested. Here, we identify Dystrophin as being required only for the maintenance of myonuclear spacing. Furthermore, we demonstrate that Dystrophin genetically interacts with Msp300, a gene encoding a KASH-domain protein, to maintain myonuclear spacing. Mechanistically, both Dystrophin and Msp300 regulate microtubule organization. Specifically, in animals with disrupted expression of both Dystrophin and Msp300, microtubule colocalization with thin filaments is reduced. Taken together, these data indicate that the peripheral membrane protein Dystrophin and the outer nuclear membrane protein Msp300 together regulate the organization of the microtubule network, which then acts as an anchor to restrict myonuclear movement in contractile myofibers. These data are consistent with growing evidence that myonuclear movement and myonuclear spacing are crucial to muscle development, muscle function and muscle repair, and provide a mechanism to connect disparate muscle diseases.