The bipolar kinesin-5 Cin8 switches from minus- to plus-end-directed motility under various conditions in vitro. The mechanism and physiological significance of this switch remain unknown. Here, we show that under high ionic strength conditions, Cin8 moves towards and concentrates in clusters at the minus ends of stable and dynamic microtubules. Clustering of Cin8 induces a switch from fast minus- to slow plus-end-directed motility and forms sites that capture antiparallel microtubules (MTs) and induces their sliding apart through plus-end-directed motility. In early mitotic cells with monopolar spindles, Cin8 localizes near the spindle poles at microtubule minus ends. This localization is dependent on the minus-end-directed motility of Cin8. In cells with assembled bipolar spindles, Cin8 is distributed along the spindle microtubules. We propose that minus-end-directed motility is required for Cin8 clustering near the spindle poles before spindle assembly. Cin8 clusters promote the capture of microtubules emanating from the neighboring spindle poles and mediate their antiparallel sliding. This activity is essential to maximize microtubule crosslinking before bipolar spindle assembly and to induce the initial separation of the spindle poles.
The authors declare no competing or financial interests.
L.G. and J.A.-B. conceived and supervised the study; O.S., A.G. and L.G. performed experiments; O.S. and L.G. analyzed data; L.G. and J.A.-B. wrote the manuscript; O.S., A.G., J.A.-B. and L.G. revised the manuscript.
This work was supported in part by the Israel Science Foundation (ISF) (grant 165/13 awarded to L.G.), the National Science Foundation (NSF-1615991), United States - Israel Binational Science Foundation (BSF-2015851 awarded to L.G. and J.A.-B.) and the National Institutes of Health (grant NIH-R01-GM11283 awarded to J.A.-B.). Deposited in PMC for release after 12 months.
Supplementary information available online at http://jcs.biologists.org/lookup/doi/10.1242/jcs.195040.supplemental
- Received July 12, 2016.
- Accepted December 29, 2016.
- © 2017. Published by The Company of Biologists Ltd