Aplip1, the homolog of JIP1, regulates myonuclear positioning and muscle stability.

During muscle development, myonuclei undergo a complex set of movements that result in evenly spaced nuclei throughout the muscle cell. In , two separate pools of Kinesin and Dynein work in synchrony to drive this process. However, how these two pools are specified is not known. Here, we investigate the role of Aplip1 (the homolog of JIP1, JIP1 is also known as MAPK8IP1), a known regulator of both Kinesin and Dynein, in myonuclear positioning. Aplip1 localizes to the myotendinous junction and has genetically separable roles in myonuclear positioning and muscle stability. In mutant embryos, there was an increase in the percentage of embryos that had both missing and collapsed muscles. Via a separate mechanism, we demonstrate that Aplip1 regulates both the final position of and the dynamic movements of myonuclei. Aplip1 genetically interacts with both Raps (also known as Pins) and Kinesin to position myonuclei. Furthermore, Dynein and Kinesin localization are disrupted in Aplip1 mutants suggesting that Aplip1-dependent nuclear positioning requires Dynein and Kinesin. Taken together, these data are consistent with Aplip1 having a function in the regulation of Dynein- and Kinesin-mediated pulling of nuclei from the muscle end.This article has an associated First Person interview with the first author of the paper.