Nucleus runs ahead of centrosome

Nucleus runs ahead of centrosome T he nucleus is not pulled by the centrosome in migrating neurons, according to a new direct imaging study by Hiroki Umeshima, Tomoo Hirano, and Mineko Kengaku (RIKEN Brain Science Institute, Wako, Japan). Previous studies showing the centrosome leading the nucleus in migrating neurons led to the suggestion that the centrosome provides the motive force for nuclear migration. “Our results clearly argue against this accepted model,” Kengaku says. The imaging study in mouse cerebellar slices indicates that the nucleus sometimes passes in front of the centrosome—a phenomenon not seen previously in isolated cells. While the nucleus spent part of its time behind the centrosome, it also jumped ahead. Neither the dynamic microtubules enveloping the nucleus or the stable microtubules extending from nucleus to leading edge converged at the centrosome. Disruption or excess formation of the stable microtubules interrupted nuclear movement. One possibility is that the stable fi laments form a track along which the nucleus is pulled by the dynamic microtubules. Inhibition of LIS1, which regulates the microtubule motor dynein, prevented migration of the nucleus without interfering with the centrosome, indicating the two use different mechanisms to migrate. What, then, is the centrosome’s role in nuclear migration? “That’s the next question we have to answer,” Kengaku says. “We think the centrosome is important for microtubule organization,” perhaps in preparing microtubules during the cyclic pauses in nuclear migration for future movements, “but we haven’t proven it yet.” Reference: Umeshima, H., et al. 2007. Proc. Natl. Acad. Sci. USA. doi:10.1073/pnas.0708047104.