Msps in red localizes to the poles (left) or polar regions (right) of the fly spindles seen in green.

Ohkura/Macmillan

Two centrosomal proteins help restrict the bulk of microtubule polymerization to the spindle, according to two papers from Fiona Cullen and Hiroyuki Ohkura (University of Edinburgh, Edinburgh, UK) and Jordan Raff (Wellcome/CRC Institute, Cambridge, UK) and colleagues.

The two Drosophila proteins, Mini-spindles (Msps) and D-TACC, have previously been shown to localize to centrosomes. Here both groups show that the two proteins physically interact. At least in female fly meiotic cells, the microtubule motor Ncd helps with the localization of Msps to spindle poles, and this localization is stabilized by the interaction with D-TACC at either conventional centrosomal spindle poles (Raff) or the acentrosomal poles that form during female fly meiosis (Cullen and Ohkura). Msps and D-TACC are the first proteins that have been localized to these unusual acentrosomal poles.

Lack of Msps leads to tripolar meiotic spindles, and overexpression of D-TACC (and subsequent recruitment of Msps to aggregates of D-TACC) results in the formation of extra microtubule asters in synctial embryos. Given the fact that Msps promotes microtubule polymerization, both groups suggest that the localization of Msps to spindle poles is essential to focus and restrict microtubule growth to a bipolar spindle. ▪

References

References
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Lee, M.J., et al.
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