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Nat Cell Biol. 2015 Apr;17(4):470-9. doi: 10.1038/ncb3131. Epub 2015 Mar 16.

Active diffusion positions the nucleus in mouse oocytes.

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CIRB, Collège de France, and CNRS-UMR7241 and INSERM-U1050, Equipe Labellisée Ligue Contre le Cancer, Paris F-75005, France.
1] Institut Curie, Centre de Recherche, Laboratoire Physico-Chimie, Paris F-75248, France [2] CNRS-UMR168, Paris F-75248, France [3] UPMC, 4 Place Jussieu, Paris F-75005, France.
UMR7600-CNRS/UPMC, 4 Place Jussieu Paris F-75005, France.
Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.


In somatic cells, the position of the cell centroid is dictated by the centrosome. The centrosome is instrumental in nucleus positioning, the two structures being physically connected. Mouse oocytes have no centrosomes, yet harbour centrally located nuclei. We demonstrate how oocytes define their geometric centre in the absence of centrosomes. Using live imaging of oocytes, knockout for the formin 2 actin nucleator, with off-centred nuclei, together with optical trapping and modelling, we discover an unprecedented mode of nucleus positioning. We document how active diffusion of actin-coated vesicles, driven by myosin Vb, generates a pressure gradient and a propulsion force sufficient to move the oocyte nucleus. It promotes fluidization of the cytoplasm, contributing to nucleus directional movement towards the centre. Our results highlight the potential of active diffusion, a prominent source of intracellular transport, able to move large organelles such as nuclei, providing in vivo evidence of its biological function.

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