Nuclear movement during myotube formation is microtubule and dynein dependent and is regulated by Cdc42, Par6 and Par3

Cells actively position their nucleus within the cytoplasm. One striking example is observed during skeletal myogenesis. Differentiated myoblasts fuse to form a multinucleated myotube with nuclei positioned in the centre of the syncytium by an unknown mechanism. Here, we describe that the nucleus of a myoblast moves rapidly after fusion towards the central myotube nuclei. This movement is driven by microtubules and dynein/dynactin complex, and requires Cdc42, Par6 and Par3. We found that Par6b and dynactin accumulate at the nuclear envelope of differentiated myoblasts and myotubes, and this accumulation is dependent on Par6 and Par3 proteins but not on microtubules. These results suggest a mechanism where nuclear movement after fusion is driven by microtubules that emanate from one nucleus that are pulled by dynein/dynactin complex anchored to the nuclear envelope of another nucleus.