Myo2p is the major motor involved in actomyosin ring contraction in fission yeast.

Cytokinesis in many eukaryotes requires an actomyosin-based contractile ring [1]. In fission yeast, cytokinesis involves the type II myosins Myo2p and Myp2p and the type V myosin Myo51p [2]. A recent study by Laplante et al.[3], using deletion mutants of myp2 and myo51 and the mis-sense mutant myo2-E1 [4], concluded that each myosin has distinct functions and proposed that Myp2p plays the dominant role in actomyosin ring contraction. Here we present evidence that Myo2p, not Myp2p, is likely to be the major motor driving actomyosin ring contractility. Since the previous work [3] was performed at 25°C, the permissive temperature for myo2-E1, we compared cytokinesis timings in myo2-E1 and myo2Δ at 25°C and found that myo2-E1 is only partially compromised at 25°C. Furthermore, we find that myp2Δ and myp2Δ myo51Δ double mutants contract actomyosin rings at ∼90% of the rate of wild-type cells at 30°C and 36°C, suggesting that Myp2p plays a minimal role in ring contraction at these temperatures. Finally, ring contraction in our myo2-E1 strain took longer at 25°C than previously reported [3]. Although faster-acting alleles of myo2 will be required to evaluate its contribution at 25°C, our work establishes that Myo2p is the major motor involved in ring contraction, under most, if not all, conditions.