MCAK-independent functions of ch-Tog/XMAP215 in microtubule plus-end dynamics.
The formation of a functional bipolar mitotic spindle is essential for genetic integrity. In human cells, the microtubule polymerase XMAP215/ch-Tog ensures spindle bipolarity by counteracting the activity of the microtubule-depolymerizing kinesin XKCM1/MCAK. Their antagonistic effects on microtubule polymerization confer dynamic instability on microtubules assembled in cell-free systems. It is, however, unclear if a similar interplay governs microtubule behavior in mammalian cells in vivo. Using real-time analysis of spindle assembly, we found that ch-Tog is required to produce or maintain long centrosomal microtubules after nuclear-envelope breakdown. In the absence of ch-Tog, microtubule assembly at centrosomes was impaired and microtubules were nondynamic. Interkinetochore distances and the lengths of kinetochore fibers were also reduced in these cells. Codepleting MCAK with ch-Tog improved kinetochore fiber length and interkinetochore separation but, surprisingly, did not rescue centrosomal microtubule assembly and microtubule dynamics. Our data therefore suggest that ch-Tog has at least two distinct roles in spindle formation. First, it protects kinetochore microtubules from depolymerization by MCAK. Second, ch-Tog plays an essential role in centrosomal microtubule assembly, a function independent of MCAK activity. Thus, the notion that the antagonistic activities of MCAK and ch-Tog determine overall microtubule stability is too simplistic to apply to human cells.
Barr
Alexis R
AR
Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge, United Kingdom.
Gergely
Fanni
F
D018385:Centrosome; D006367:HeLa Cells; D006801:Humans; D016547:Kinesins / Q000502:physiology*; D007700:Kinetics; D018386:Kinetochores; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism*; D008941:Spindle Apparatus
C454180:CKAP5 protein, human; C091489:KIF2C protein, human; D008869:Microtubule-Associated Proteins; D016547:Kinesins