Dystrophin interacts with Msp300 to Regulate Myonuclear Positioning and Microtubule Organization

During Drosophila myognesis, myonuclei are actively moved during embryogenesis, and their spacing is maintained through an anchoring mechanism in the fully differentiated myofiber. While 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 have identified a Dystrophin as required only for the maintenance of myonuclear spacing. Furthermore, we demonstrate that Dystrophin genetically interacts with the KASH-domain protein Msp300 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 sarcomeres is reduced. Taken altogether, 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 critical to muscle development, muscle function, and muscle repair and provide a mechanism to connect disparate muscle diseases. Summary StatementHere we show that Dystrophin is required to maintain the spacing of nuclei in differentiated myofibers. Furthermore, Dystrophin achieves this function via a genetic interaction with Msp300 which regulates microtubule organization.