Mechanical contributions of the Myp2 tail revealed by coiled-coil force sensors

Abstract

Cytokinesis is driven by the constriction of an actomyosin contractile ring, yet how forces generated by individual myosin molecules are transmitted within the ring remains poorly understood. In fission yeast Schizosaccharomyces pombe, the type II myosin Myp2 plays a key role in ring constriction and stability, particularly under stress conditions. Unlike typical type-II myosins, Myp2s tail contains two coiled coils. Although numerous studies have revealed the structure and molecular function of Myp2, the mechanical contribution of its unique tail region has remained unclear. Here, we directly measured forces acting on Myp2 in living cells using genetically encoded coiled-coil force sensors. Insertion of force sensors into the neck region revealed that Myp2 experiences forces of approximately 6.6 pN within the contractile ring. To dissect the contribution of the tail region, we systematically analyzed tail-deletion mutants. Deletion of the proximal tail had little effect on force levels, whereas deletion of the distal C-terminal tail significantly reduced the forces experienced by Myp2. Quantitative analysis of force distributions further showed that truncation of the C-terminal tail reduces the characteristic force by approximately half, demonstrating a major mechanical contribution of the distal tail to the forces experienced by Myp2 at the molecular scale. Deletion of the C-terminal tail slowed the growth rate, consistent with previous macroscopic observations that this region is required for robust ring constriction under stress conditions. We further found that the C-terminal tail forms clusters, which require full-length Myp2 for proper localization to the ring. These findings, together with molecular force measurements and quantitative analysis, demonstrate that the Myp2 tail is not merely a structural or regulatory domain but functions as a load-bearing component in vivo, with its C-terminal region playing a central role in force transmission across scales.