The Centrosome Controls the Number and Spatial Distribution of Microtubules by Negatively Regulating Alternative MTOCs

1 In this work, we have investigated in mammalian cells how microtubule nucleation at 2 centrosome and Golgi apparatus are coordinated, using genetic ablation of three g-TuRC 3 binding proteins -AKAP450, Pericentrin and CDK5Rap2and the PLK4 inhibitor centrinone. We 4 show that centrosomal microtubule nucleation is independent of Golgi activity whereas the 5 converse is not true: nucleation on the Golgi negatively correlates with the number of 6 centrosomes. In addition, depleting AKAP450 in cells lacking centrioles, that abolishes Golgi 7 nucleation activity, leads to microtubule nucleation from numerous cytoplasmic Golgi8 unbound acentriolar structures containing Pericentrin, CDK5Rap2 and g-tubulin. Strikingly, 9 centrosome-less cells display twice higher microtubule density than normal cells, suggesting 10 that the centrosome controls the spatial distribution of microtubules, not only by nucleating 11 them, but also by acting as a negative regulator of alternative MTOCs. Collectively, the data 12 reveals a hierarchical control of microtubule nucleation, with the centrosome regulating this 13 process in a more complex manner than usually thought. It also unveils mechanisms that could 14 help understanding MT network reorganization during cell differentiation. 15 16 2 not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/153304 doi: bioRxiv preprint first posted online Jun. 21, 2017;