Fibrillarin redistributes to the spindle poles and partially colocalizes with NuMA during mitosis

Fibrillarin, a major protein in the nucleolus, is known to redistribute during mitosis from the nucleolus to the cytosol, and is related to the dynamics of post-mitotic reassembly of the nucleolus. To better understand the dynamic behavior and the relationship with other cytoplasmic structures, we have now expressed fibrillarin-pDsRed1 fusion protein in HeLa cells. The results showed that a part of fibrillarin was associated with mitotic spindle poles in the mitotic cells. Nocodazole-induced microtubule depolymerization resulted in fibrillarin redistribution throughout the cytoplasm, and removal of nocodazole resulted in relocalization of fibrillarin at the polar region during the mitotic spindles reassembly. In a mitotic cell free system, fibrillarin was found in the center of taxol-induced microtubule asters. Moreover, fibrillarin was found to colocalize with the nuclear mitotic apparatus protein (NuMA) at the poles of mitotic cells. Therefore, it is postulated that the polar redistribution of fibrillarin is mediated by microtubules.