LOCALIZATION OF NUMA PROTEIN ISOFORMS IN THE NUCLEAR MATRIX OF MAMMALIAN-CELLS

Using a monoclonal antibody 2D3 generated against a kinetochore-enrich ed human chromosome preparation, we identified a high molecular mass p rotein with nuclear staining in interphase and polar staining of the p ericentriolar region in the mitotic spindle. Initially termed centroph ilin, this protein associates with the minus-ends of spindle microtubu les (MT) and appears to be important in spindle organization [Tousson et al., 1991: J. Cell Biol. 112:427-440]. Comparison of a partial cDNA sequence obtained for centrophilin with the full length cDNA sequence of nuclear mitotic apparatus protein (NuMA) [Compton et al., 1992: J. Cell Biol. 116:1395-1408; Yang et al., 1992: J. Cell Biol. 116:1303-1 317] has indicated that NuMA and centrophilin are the same protein. Us ing a polyclonal NuMA antibody, we have provided further evidence that NuMA exists as isoforms as shown by peptide mapping and immunoblots. Sequential fractionation experiments along with immunofluorescence, im munoblotting, and EM immunogold labeling have demonstrated that NuMA i soforms are novel components of nuclear core filaments. Thus, NuMA, a long coiled-coil protein, appears to have dual functions in interphase and mitosis during the cell cycle. In interphase, NuMA likely plays a structural role in the nucleoskeleton that may be important in nuclea r organization and functions, whereas in mitosis, NuMA appears to be a ssociated with spindle MT organization and chromosome positioning. (C) 1994 Wiley-Liss, Inc.