SUMMARY Loss of function of a cell cycle-associated gene NEK1 causes amyotrophic lateral sclerosis (ALS), but how this leads to motor neuron degeneration is unknown. We studied the function of NEK1 in human stem cell-derived motor neurons and found that loss of NEK1 causes decreased neurite length accompanied by transcriptional alterations. We also found that NEK1 interacts with and modulates the formation of the retromer, and that impaired retromer function contributes to neurite outgrowth deficits. We identified SMC3, which interacts with NEK1 during the cell cycle, as a kinase substrate of NEK1 in motor neurons. Notably, loss of SMC3 not only recapitulates the decreased neurite outgrowth, but also affects retromer formation. We suggest that NEK1 interacts with multiple proteins in postmitotic neurons to coordinate retromer formation, and that loss of this leads to impaired neurite outgrowth.

NEK1 modulates neurite outgrowth in motor neurons through coordinating retromer formation