Dynamics of dynein at microtubule plus-ends and the cortex during the division of the C. elegans zygote

During asymmetric cell divisions, cortical dyneins generate forces essential to position the spindle after polarity cues, prescribing daughter cells fate. In nematode zygote, cortical dynein pulls on microtubules transiently, raising the question of its targeting and dynamics. Tracking and fluorescence correlation spectroscopy revealed that in the cytoplasm, dynein spots displayed directed motions toward the cortex, localized at microtubule plus-ends through EBP-2/EB but are not actively transported. Surprisingly CLIP-1/CLIP170 is not involved. ebp-2(0) slightly reduced spindle rocking, thus most cortical forces remain suggesting a redundant mechanism. At the cortex, to relate dynein residency and forces generating, we tracked dynein and found two dynamically distinct populations. One of them would correspond to force generating events. Our experiments also indicated that an asymmetric (polarized) dynein-microbutule on-rate, causes the force imbalance positioning the spindle. GPR-1/2 increases the overall dynein density but also residency time (pulling processivity), although this latter was not polarized.