Osorio, D. S. | Search bioRxiv

bioRxiv2018

Flow-independent accumulation of motor-competent non-muscle myosin II in the contractile ring is essential for cytokinesis

Cytokinesis in animal cells requires the assembly of a contractile actomyosin ring, whose subsequent constriction physically separates the two daughter cells. Non-muscle myosin II (myosin) is essential for cytokinesis, but the role of its motor activity remains poorly defined. Here, we examine cytokinesis in C. elegans one-cell embryos expressing myosin motor mutants generated by genome editing. Motor-dead myosin, which is capable of binding F-actin, does not support cytokinesis, and embryos co-expressing motor-dead and wild-type myosin are delayed in cytokinesis. Partially motor-impaired myosin also delays cytokinesis and renders contractile rings more sensitive to reduced myosin levels. Thus, myosin motor activity, rather than its ability to cross-link actin filaments, drives contractile ring assembly and constriction. We further demonstrate that myosin motor activity is required for long-range cortical actin flows, but that flows per se play a minor role in contractile ring assembly. Our results suggest that flow-independent recruitment of motor-competent myosin to the cell equator is both essential and rate-limiting for cytokinesis.

cell biology↗

bioRxiv2017

TPXL-1 Activates Aurora A to Clear Contractile Ring Components from the Polar Cortex During Cytokinesis

During cytokinesis, a signal from the bundled microtubules that form between the separating anaphase chromosomes promotes the accumulation of contractile ring components at the cell equator, while a signal from the centrosomal microtubule asters inhibits accumulation of contractile ring components at the cell poles. However, the molecular identity of the inhibitory signal has remained unknown. To identify molecular components of the aster-based inhibitory signal, we developed a means to monitor the removal of contractile ring proteins from the polar cortex after anaphase onset. Using this assay, we show that polar clearing is an active process that requires activation of Aurora A kinase by TPXL-1. TPXL-1 concentrates on astral microtubules coincident with polar clearing in anaphase, and its ability to recruit Aurora A and activate its kinase activity are essential for clearing. In summary, our data identify Aurora A kinase as an aster-based inhibitory signal that restricts contractile ring components to the cell equator during cytokinesis.\n\nSUMMARYDuring cytokinesis, centrosomal asters inhibit cortical contractility at the cell poles. Mangal et al. provide molecular insight into this phenomenon, showing that TPXL-1, which localizes to astral microtubules, activates Aurora A kinase to clear contractile ring proteins from the polar cortex.

cell biology↗