Figure 7.

Models for the polarity paradox of the sequential action of kinesin-1 and cytoplasmic dynein during meiotic spindle positioning. In both models, the cytoplasmic microtubule array has microtubules with plus ends pointed toward the cortex with kinesin-1 bound to the spindle through KCA-1, pulling the spindle with a net pulling force toward the cortex. (A) On APC activation, inhibitors of dynein motility and/or astral microtubule growth are proteolyzed. Dynein would be transported on the growing plus ends of astral microtubules and be activated upon docking at a cortical site, where it would generate a cortical pulling force acting on spindle poles. (B) Alternatively, upon APC activation, microtubules are nucleated at the cortex resulting in a majority of cytoplasmic microtubules with minus ends pointed toward the cortex. Dynein at spindle poles would be attached to the spindle through the cargo-binding domain to allow the motor domains to interact with this new population of cytoplasmic microtubules.