Wang et al. reveal how two proteins cluster the myosin motor Myo51 to promote assembly of the fission yeast cytokinetic ring.
Fission yeast assemble a contractile ring from myosin II–containing precursor nodes scattered around the cell equator. The motor protein captures actin filaments nucleated from neighboring nodes and pulls the structures together until they coalesce into a compact actomyosin ring. The type V myosin Myo51 also contributes to ring formation by promoting the delivery of additional actin filaments to the cell equator. But Myo51’s precise function and how it is regulated during cytokinesis remain unclear.
Wang et al. identified two coiled-coil proteins, which they named Rng8 and Rng9, that colocalized with Myo51 on actin cables and the cytokinetic ring. Deleting Rng8 or Rng9 largely abolished Myo51’s recruitment to these structures, thereby delaying node coalescence and ring assembly.
All three proteins interacted with each other in vivo, forming higher-order clusters containing multiple Myo51 dimers. These clusters were able to move without interruption along actin filaments, transporting artificial cargoes long distances across the cell. In the absence of Rng8 or Rng9, however, Myo51 only formed individual dimers that failed to move processively on actin cables.
Rng8 and Rng9 therefore support Myo51’s function in cytokinesis by regulating the motor’s localization and oligomerization. Senior author Jian-Qiu Wu now wants to investigate the motor complex’s behavior in vitro and to identify any cargoes (besides actin filaments) that it might transport to promote contractile ring assembly and stability.
Text by Ben Short