Nuclear-mitotic apparatus protein: a structural protein interface between the nucleoskeleton and RNA splicing

Vertebrate splicing factors are localized to discrete domains within the nuclei of somatic cells. The mechanism whereby such nuclear domains, identified as speckles by immunofluorescence microscopy, are generated is unclear. Recent studies suggest that the spatial order within the nucleus is maintained by nuclear matrix factors. Here we show that a protein in the nuclear matrix and mitotic apparatus [nuclear-mitotic apparatus protein, NuMA; Lydersen, B. & Pettijohn, D. (1980) Cell 22, 489-499] colocalizes with splicing factors in interphase nuclei and is associated with small nuclear ribonucleoproteins in a complex immunoprecipitated from HeLa extract with small nuclear ribonucleoprotein antibodies. Moreover, NuMA associates with splicing complexes that are reconstituted in vitro using wild-type pre-mRNA, but not with nonspecific RNA. Cumulatively, these observations suggest a function of NuMA or NuMA-like proteins in interphase cells in providing a bridge between RNA processing and the nucleoskeleton.

Localization of NuMA protein isoforms in the nuclear matrix of mammalian cells

Using a monoclonal antibody 2D3 generated against a kinetochore-enriched human chromosome preparation, we identified a high molecular mass protein with nuclear staining in interphase and polar staining of the pericentriolar region in the mitotic spindle. Initially termed centrophilin, this protein associates with the minus-ends of spindle microtubules (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. 116:1303-1317] has indicated that NuMA and centrophilin are the same protein. Using 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, immunoblotting, and EM immunogold labeling have demonstrated that NuMA isoforms 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 nuclear organization and functions, whereas in mitosis, NuMA appears to be associated with spindle MT organization and chromosome positioning.

[A study on developmental toxicity of vanadium pentoxide in Wistar rats]

Timed-pregnant Wistar rats were injected intraperitoneally with V2O5 at 0.33, 1.0 and 3.0 mg/kg/day on days 6-15 of gestation. Maternal toxic symptoms, decreased of weight gain during treatment and placenta weight, increased incidence of embryo-fetus mortality and external or skeletal malformation and fetal growth retardation were observed in the 3.0 mg/kg group. Increased incidence of embryo-fetus mortality and external or skeletal malformation, delayed ossification of bone and decreased placenta weight were observed in the 1.0 mg/kg group. These results indicate that V2O5 is a developmental toxicant with or without obvious maternal toxicity in Wistar rats. Although vanadium can be accumulated in placenta, it could passed through placenta. In this study, vanadium could induce a decrease of placenta weight without obvious maternal toxicity, and an A/D ratio of 3 was noted. These results suggest that vanadium may exert a direct effect on embryo-fetues or a "double effect" on the placenta function and embryo-fetus both. It has been reported that vanadium does not increase mal formation in NIN, Kunming, Swiss, NMRI mice or Syrian golden hamster. The dose for inducing developmental toxicity of vanadium in mice is higher than that in rats. This suggests that rats be more sensitive than mice to the developmental toxicity of vanadium.

Centrophilin: a novel mitotic spindle protein involved in microtubule nucleation

A novel protein has been identified which may serve a key function in nucleating spindle microtubule growth in mitosis. This protein, called centrophilin, is sequentially relocated from the centromeres to the centrosomes to the midbody in a manner dependent on the mitotic phase. Centrophilin was initially detected by immunofluorescence with a monoclonal, primate-specific antibody (2D3) raised against kinetochore-enriched chromosome extract from HeLa cells (Valdivia, M. M., and B. R. Brinkley. 1985. J. Cell Biol. 101:1124-1134). Centrophilin forms prominent crescents at the poles of the metaphase spindle, gradually diminishes during anaphase, and bands the equatorial ends of midbody microtubules in telophase. The formation and breakdown of the spindle and midbody correlates in time and space with the aggregation and disaggregation of centrophilin foci. Immunogold EM reveals that centrophilin is a major component of pericentriolar material in metaphase. During recovery from microtubule inhibition, centrophilin foci act as nucleation sites for the assembly of spindle tubules. The 2D3 probe recognizes two high molecular mass polypeptides, 180 and 210 kD, on immunoblots of whole HeLa cell extract. Taken together, these data and the available literature on microtubule dynamics point inevitably to a singular model for control of spindle tubule turnover.

Polyethylene glycol significantly enhances the transfer of membrane immunoblotting

Poly(ethylene glycol)n is a group of water-soluble, hydrophobic, optically transparent and biomacromolecule-nondenaturing polymers. These properties have caused it be widely used for various purposes in the biological sciences. In this study, the effects of poly(ethylene glycol)n on protein preservation, electrotransferring, and immunoblotting from sodium dodecyl sulfate (SDS)-polyacrylamide gel onto polyvinylidene difluoride (PVDF) membrane have been systematically evaluated. After SDS-polyacrylamide gel electrophoresis, 30% poly(ethylene glycol)n may be applied to reversibly fix proteins within the gel more completely, differing from irreversible fixation produced by solutions such as trichloroacetic acid-sulfosalicylic acid or acetic acid-methanol systems. The intragel proteins, fixed by poly(ethylene glycol)n, can be electroblotted directly onto PVDF membranes in the presence of 30% poly(ethylene glycol)n. We have shown that treatment with poly(ethylene glycol)n may reduce background, raise signal-to-noise ratio, sharpen protein bands, and increase resolution, resulting in enhancement of the immunoblotting transfer. It is possible to visualize a few picograms of a single protein band, increasing the sensitivity of the method by 10- to 100-fold, as compared with standard immunoblotting techniques.