Myosin II regulatory light chain phosphorylation and formin availability modulate cytokinesis upon changes in carbohydrate metabolism.
Cytokinesis, which achieves the separation of daughter cells after mitosis completion, relies in animal cells on a contractile actomyosin ring (CAR), made of actin and class II myosins, whose activity is heavily influenced by regulatory light chain (RLC) phosphorylation. However, in simple eukaryotes such as fission yeast Schizosaccharomyces pombe, regulation of CAR dynamics by RLC phosphorylation seems dispensable. We found that redundant phosphorylation at Ser35 of the S. pombe RLC homolog Rlc1 by the p21-activated kinases Pak1 and Pak2, modulates Myosin II Myo2 activity and becomes essential for cytokinesis and cell growth during respiration. Previously, we showed that the Stress Activated Protein Kinase Pathway (SAPK) MAPK Sty1 controls fission yeast CAR integrity by downregulating formin For3 levels (Gomez-Gil et al.,2020). Here we report that reduced availability of formin For3-nucleated actin filaments for the CAR is the main reason for the required control of myosin II contractile activity by RLC phosphorylation during respiration-induced oxidative stress. Hence, recovery of For3 levels with antioxidants bypasses the control of Myosin II function regulated by RLC phosphorylation to allow cytokinesis and cell proliferation during respiration. Therefore, a fine-tuned interplay between Myosin II function by Rlc1 phosphorylation and environmentally controlled actin filament availability is critical for a successful cytokinesis in response to a switch to a respiratory carbohydrate metabolism.