Antoine Guichet

Microtubules and their associated motors are important players in nucleus positioning. Although nuclear migration in Drosophila oocytes is controlled by microtubules, a precise role for microtubule-associated molecular motors in nuclear migration has yet to be reported. We characterize novel landmarks that allow a precise description of the pre-migratory stages. Using these newly defined stages, we report that, before migration, the nucleus moves from the oocyte anterior side toward the center and concomitantly the centrosomes cluster at the posterior of the nucleus. In the absence of Kinesin-1, centrosome clustering is impaired and the nucleus fails to position and migrate properly. The maintenance of a high level of Polo-kinase at centrosomes prevents centrosome clustering and impairs nuclear positioning. In the absence of Kinesin-1, SPD-2, an essential component of the pericentriolar material, is increased at the centrosomes, suggesting that Kinesin-1-associated defects result from a failure to reduce centrosome activity. Consistently, depleting centrosomes rescues the nuclear migration defects induced by Kinesin-1 inactivation. Our results suggest that Kinesin-1 controls nuclear migration in the oocyte by modulating centrosome activity.