Single-particle tracking of dynein identifies PP2A B55/SUR-6 as a cell cycle regulator of cortical force generation

Convergence and positioning of the pronuclei and mitotic spindle of many zygotes aids efficient division and is essential for early embryonic patterning. In the C. elegans zygote, interactions between microtubules and cortically anchored dynein are key to early development. However, how cortical microtubule pulling forces are controlled through the cell cycle is less well understood. We used single-molecule imaging and a windowed mean squared displacement analysis to uncover the behavior of dynein during cortical force generation, and provide a regulatory role for protein phosphatase PP2A-B55/SUR6 via NuMA-like protein LIN-5 in this process. Previous findings and our results suggest that PP2A regulates cortical microtubule pulling forces by increasing dynein binding and unbinding to the cortical force generation complex. Our data also suggests that cortical occupancy of dynein is abrogated to vary force generation. Our approach will be broadly applicable to classify the force generation behavior of single molecules in living organisms.