Microtubule plus-ends act as physical signaling hubs to activate RhoA during cytokinesis.

Abstract

Microtubules (MTs) are essential for cleavage furrow positioning during cytokinesis, but the mechanisms by which MT-derived signals spatially define regions of cortical contractility are unresolved. In this study cytokinesis regulators visualized in <i>Drosophila melanogaster</i> (<i>Dm</i>) cells were found to localize to and track MT plus-ends during cytokinesis. The RhoA GEF Pebble (<i>Dm</i> ECT2) did not evidently tip-track, but rather localized rapidly to cortical sites contacted by MT plus-tips, resulting in RhoA activation and enrichment of myosin-regulatory light chain. The MT plus-end localization of centralspindlin was compromised following EB1 depletion, which resulted in a higher incidence of cytokinesis failure. Centralspindlin plus-tip localization depended on the C-terminus and a putative EB1-interaction motif (hxxPTxh) in RacGAP50C. We propose that MT plus-end-associated centralspindlin recruits a cortical pool of <i>Dm</i> ECT2 upon physical contact to activate RhoA and to trigger localized contractility.