The myosin regulatory light chain Myl5 localizes to mitotic spindle poles and is required for proper cell division

Myosins are ATP-dependent actin-based molecular motors critical for diverse cellular processes like intracellular trafficking, cell motility and cell invasion. During cell division, myosin MYO10 is important for proper mitotic spindle assembly, the anchoring of the spindle to the cortex, and positioning of the spindle to the cell mid-plane, while myosin MYO2 functions in actomyosin ring contraction to promote cytokinesis. However, myosins are regulated by myosin regulatory light chains (RLCs), and whether RLCs are important for cell division has remained unexplored. Here, we have determined that the previously uncharacterized myosin RLC Myl5 associates with the mitotic spindle and is required for cell division. Myl5 localized to the mitotic spindle poles and spindle microtubules during early mitosis, an area overlapping with MYO10 localization. Depletion of Myl5 led to defects in chromosome congression and to a slower progression through mitosis. We propose that Myl5 is a novel myosin RLC that is important for cell division.