The chromosomal passenger complex (CPC), composed of Aurora-B, INCENP, borealin and survivin, is important for cytokinesis as it coordinates the site of contractile ring formation and the timing of its constriction. However, the specific roles of survivin within the CPC are not clear. In this article, Shoshana Ravid and colleagues (Babkoff et al., 2019) now report that survivin directly interacts with non-muscle myosin II isoform B (NMIIB) in vivo, and that this interferes with the ability of NMIIB to form filaments. Survivin and NMIIB mainly co-localise at the equatorial cortex during telophase, suggesting that formation of the contractile ring in other regions is prevented due to sequestering of NMIIB monomers. The authors also show that CDK1-mediated phosphorylation of survivin inhibits its interaction with NMIIB before anaphase onset, while the rapid decline of CDK1 in telophase and subsequent dephosphorylation of survivin allow its binding to NMIIB, thus providing a timing mechanism. Furthermore, disruption of the survivin–NMIIB complex leads to multiple mitotic defects, including some caused by NMIIB over-assembly, underscoring the importance of this interaction for successful cell division. Finally, the authors demonstrate that only survivin in homodimers interacts with NMIIB, answering the debate over whether homodimerisation of survivin is required for its function. This work thus describes a crucial role of survivin in the spatio-temporal regulation of cytokinesis.
