Drosophila adult muscle precursor cells contribute to motor axon pathfinding and proper innervation of embryonic muscles

Despites several decades of studies on the neuromuscular system, the relationship between muscle stem cells and motor neurons remains elusive. Using the Drosophila model, we provide evidences that adult muscle precursors (AMPs), the Drosophila muscle stem cells, interact with the motor axons during embryogenesis. AMPs not only hold the capacity to attract the navigating intersegmental (ISN) and segmental a (SNa) nerve branches, but are also mandatory to the innervation of muscles in the lateral field. This so far ignored AMPs role involves their filopodia-based interactions with nerve growth cones. In parallel, we report the previously undetected expression of encoding guidance molecules sidestep and side IV in AMPs. Altogether, our data support the view that Drosophila muscle stem cells represent spatial landmarks for navigating motor neurons and reveal that their positioning is critical for the muscles innervation in the lateral region. Furthermore, AMPs and motor axons are interdependent as the genetic ablation of SNa leads to a specific loss of SNa-associated lateral AMPs.