Tissue maintenance requires adequate cell proliferation and a directed plane of cell division. Retraction fibres can determine the plane of cell division by directing spindle movements; however, retraction fibre components that direct spindle movements remain unclear. We report MARK2/Par1b kinase as a novel component of actin-rich retraction fibres, important for directed spindle movements. A kinase-dead mutant of MARK2 reveals MARK2’s ability to monitor actin status. MARK2’s localisation at retraction fibres, but not the rest of the cortical membrane or centrosome, is dependent on its kinase activity, highlighting a specialised spatial regulation of MARK2. By subtly perturbing the actin cytoskeleton, we demonstrate MARK2’s role in correcting spindle off-centering, induced by lesions in actin assembly. In addition to this mitotic role, we show MARK2’s post-mitotic role in ensuring normal G1-S progression and cell proliferation. We propose that MARK2 provides a molecular framework to integrate cortical signals and cytoskeletal changes in both mitosis and interphase. Short Summary Coordination of cell proliferation and division is important for tissue maintenance. We report a regulated localisation for MARK2 in mitosis and interphase. We demonstrate its mitotic role in correcting spindle positioning defects and its interphase role in G1-S transition.
