.
In this model, plus-end-directed motor proteins operating on interacting antiparallel microtubules help separate the two poles of a forming mitotic spindle. New microtubules grow out in random directions from two nearby centrosomes. The microtubules are anchored at the centrosome by their minus ends, while their plus ends extend outward. When two microtubules from opposite centrosomes interact in an overlap zone, plus-end-directed, kinesin-related motor proteins cross-link the microtubules together and tend to drive the microtubules in the direction that will push the centrosomes apart (see Figure 18-13B
). Minus-end-directed dynein motors associated with the nuclear envelope are also thought to help separate the two centrosomes by pulling on the two sets of astral microtubules (not shown).
). Minus-end-directed dynein motors associated with the nuclear envelope are also thought to help separate the two centrosomes by pulling on the two sets of astral microtubules (not shown).