The human microtubule crosslinking protein prc1 acts like a viscous dashpot to resist microtuble sliding during mitosis

Abstract

The results indicated that the resistive forces generated by PRC1 crosslinked microtubule bundles scale with sliding velocity and the number of PRC1 within the bundle. Interestingly, the resistive forces measured were independent of microtubule bundle overlap length or PRC1 density within the bundle overlaps. From the data I argue that PRC1 acts as a mechanical dashpot indicating that the resistive forces generated by PRC1 ensembles scale proportionately to the velocity at which the bundle is being pulled apart. This behavior would generate higher resistance to fast acting motor proteins such as dynein while producing minimal resistance to slower acting motors such as kinesin-5 or kinesin-14 thereby playing an important role in the maintenance of a steady-state mitotic spindle.

The eukaryotic mitotic spindle is a highly dynamic structure composed primarily of microtubules organized by motor and non-motor microtubule associated proteins (MAP’s). These protein-microtubule ensembles produce various pull-push forces at different rates as the spindle undergoes the multiple stages of mitosis. Strikingly, the spindle manages to maintain a steady-state throughout the entire mitotic process despite the various forces generated at multiple rates by microtubule-MAP interactions. The MAP PRC1 is one such protein which crosslinks microtubules in an antiparallel orientation within the central spindle and has been hypothesized to generate a resistive force to active motor protein microtubule sliding. The research presented within this document sought to recapitulate the activity of PRC1 and to quantify the hypothesized resistive forces. This was accomplished by reconstituting PRC1 crosslinked microtubule bundles and applying the techniques Total Internal Reflection Fluorescence Microscopy (TIRF) microscopy and optical trapping to measure the resistive forces using multiple parameters.