The Timing of Midzone Stabilization during Cytokinesis Depends on Myosin II Activity and an Interaction between INCENP and Actin

Abstract

The final steps of cell division are tightly coordinated in space and time, but whether mechanisms exist to couple the actin and microtubule (MT) cytoskeletons during anaphase and cytokinesis (C phase) is largely unknown. During anaphase, MTs are incorporated into an anti-parallel array termed the spindle midzone (midzone MTs), whereas F-actin and non-muscle myosin II, together with other factors, organize into the cleavage furrow [1]. Previous studies in somatic cells have shown that midzone MTs become highly stable after furrows have begun ingression [2], indicating that furrow-to-MT communication may occur. Midzone formation is also inhibited in fly spermatocytes that fail to form a cleavage furrow [3] and during monopolar cytokinesis when myosin contractility is blocked by blebbistatin [4]. We show here that midzone MT stabilization is dependent on actomyosin contraction, suggesting that there is active coordination between furrow ingression and microtubule dynamics. Midzone microtubule stabilization also depends on the kinase activity of Aurora B, the catalytic subunit of the chromosomal passenger complex (CPC), uncovering a feedback mechanism that couples furrowing with microtubule dynamics. We further show that the CPC scaffolding protein INCENP (inner centromere protein) binds actin, an interaction that is important for cytokinesis and for midzone MT stabilization following furrow ingression. Stabilization of midzone MTs with low amounts of Taxol rescues cytokinesis in INCENP actin-binding mutant-expressing cells. Collectively, our work demonstrates that the actin and microtubule cytoskeletons are coordinated during cytokinesis and suggests that the CPC is integral for coupling furrow ingression with midzone microtubule stabilization.