Some of my favorite proteins ride on the ends of microtubules. I don’t usually like to anthropomorphize proteins, but I always think of Dr. Strangelove hopping on the growing end of a microtubule (and I didn’t even like that movie!). Today’s image is from a paper that adds a satisfying piece to the mitotic spindle puzzle.
Astrin is a mitotic spindle protein that is required for proper alignment of chromosomes on the metaphase plate during mitosis. It wasn’t clear exactly what astrin is doing to promote chromosome alignment, or how astrin arrives at the right location. A recent paper paints a much more complete astrin story. Dunsch and colleagues found a novel protein called kinastrin that forms a complex with astrin and a few others. Astrin localizes to the plus ends of microtubules, and requires kinastrin to do so. The presence of this complex may be affecting microtubule dynamics directly, consistent with the chromosome alignment and spindle integrity problems seen in kinastrin- and astrin-depleted cells. Image above shows fluorescently-tagged astrin localized to the ends of microtubules. The different colors show the localization of astrin in subsequent time-lapse images (ie, the astrin moves with the end of the microtubule).
Dunsch, A., Linnane, E., Barr, F., & Gruneberg, U. (2011). The astrin-kinastrin/SKAP complex localizes to microtubule plus ends and facilitates chromosome alignment originally published in The Journal of Cell Biology, 192 (6), 959-968 DOI: 10.1083/jcb.201008023