A Minimal Midzone Protein Module Controls Formation and Length of Antiparallel Microtubule Overlaps

SummaryDuring cell division, microtubules are arranged in a large bipolar structure, the mitotic spindle, to segregate the duplicated chromosomes. Antiparallel microtubule overlaps in the spindle center are essential for establishing bipolarity and maintaining spindle stability throughout mitosis. In anaphase, this antiparallel microtubule array is tightly bundled forming the midzone, which serves as a hub for the recruitment of proteins essential for late mitotic events. The molecular mechanism of midzone formation and the control of its size are not understood. Using an in vitro reconstitution approach, we show here that PRC1 autonomously bundles antiparallel microtubules and recruits Xklp1, a kinesin-4, selectively to overlapping antiparallel microtubules. The processive motor Xklp1 controls overlap size by overlap length-dependent microtubule growth inhibition. Our results mechanistically explain how the two conserved, essential midzone proteins PRC1 and Xklp1 cooperate to constitute a minimal protein module capable of dynamically organizing the core structure of the central anaphase spindle.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (223 K)Download as PowerPoint slideHighlights► PRC1 autonomously recognizes antiparallel microtubule overlaps ► PRC1 recruits kinesin-4 to antiparallel microtubule overlaps ► Kinesin-4 locally inhibits microtubule growth in antiparallel overlaps ► PRC1 and kinesin-4 generate a “minimal midzone” with controlled length in vitro