The star of the Inner Life of the Cell was the kinesin motor protein pulling a large vesicle along a microtubule. But there are many variants of kinesin that transport different cargo. For example, klp2p (kinesin-14) can pull other microtubules to regions within the cell where overlapping microtubules can be cross-linked by microtubule-associating proteins and thus serve as new nucleation sites. Researchers at the University of Pennsylvania School of Medicine have published a study in Cell ("Crosslinkers and Motors Organize Dynamic Microtubules to Form Stable Bipolar Arrays in Fission Yeast") that outlines a mechanism for the development of such nucleation sites involving an interplay between the motor ability of the kinesin and the brake-like abilities of the cross-linkers. What's fun is that they include a short video of the kinesins at work. If you watch the second video, you'll see the kinesins within the cell as green dots zoom along microtubules (red lines).

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