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Abstract
Kinetochores must continuously associate with dynamic microtubule plus ends, as they oscillate along the mitotic spindle. The molecular basis for the kinetochore to track microtubule plus ends remains unresolved. In a recent study, we have shown an essential role of the formin mDia3 in stable kinetochore microtubule attachment and metaphase chromosome alignment. This function is attributable to EB1-binding by mDia3, for replacing endogenous mDia3 with an EB1-binding deficient mutant results in chromosome misalignment. EB1 specifically targets to attached, antipoleward kinetochores with polymerizing microtubules during chromosome oscillation. Therefore, we speculate that the mDai3-EB1-APC complex formation may relay EB1 microtubule plus end-tracking activity to the kinetochore.
Acknowledgments
We are grateful to Y. Guo and S. Ahmad for critically reading the manuscript. Y. Mao is an Irma T. Hirschl Career Scientist.
Figures and Tables
Figure 1 A Model for kinetochores tracking spindle microtubule plus-ends. During metaphase chromosome oscillation, the leading and trailing kinetochores in a sister kinetochore pair have two distinct stably attached microtubule populations: the trailing kinetochore is attached to growing microtubules, whereas the leading kinetochore retains its attachment to shrinking microtubules. The Ndc80 complex is a central component in stabilizing end-on kinetochore microtubule attachment. Microtubule plus-end tracking proteins, EB1 and APC, track plus ends of growing microtubules. The interaction between EB1-APC and formin mDia3, a novel kinetochore protein, may mediate continuous Ndc80 tip tracking with growing microtubules, either directly or through other unknown linker proteins. The Ska complex is able to mediate a cargo association with depolymerizing microtubule plus ends in vitro.Citation27 Whether the Ska complex is able to interact with Ndc80 and increase the stability of connection between Ndc80 and shrinking microtubule ends is not clear.
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