Metaphase

Abstract: This report describes the use of fluorescence in situ hybridization for chromosome classification and detection of chromosome aberrations. Biotin-labeled DNA was hybridized to target chromosomes and subsequently rendered fluorescent by successive treatments with fluorescein-labeled avidin and biotinylated anti-avidin antibody. Human chromosomes in human-hamster hybrid cell lines were intensely and uniformly stained in metaphase spreads and interphase nuclei when human genomic DNA was used as a probe. Interspecies translocations were detected easily at metaphase. The human-specific fluorescence intensity from cell nuclei and chromosomes was proportional to the amount of target human DNA. Human Y chromosomes were fluorescently stained in metaphase and interphase nuclei by using a 0.8-kilobase DNA probe specific for the Y chromosome. Cells from males were 40 times brighter than those from females. Both Y chromosomal domains were visible in most interphase nuclei of XYY amniocytes. Human 28S ribosomal RNA genes on metaphase chromosomes were distinctly stained by using a 1.5-kilobase DNA probe.

Abstract: Chromosomes can be specifically stained in metaphase spreads and interphase nuclei by in situ hybridization with entire chromosome-specific DNA libraries. Unlabeled human genomic DNA is used to inhibit the hybridization of sequences in the library that bind to multiple chromosomes. The target chromosome can be made at least 20 times brighter per unit length than the others. Trisomy 21 and translocations involving chromosome 4 can be detected in metaphase spreads and interphase nuclei by using this technique.

Abstract: Oscillations in the activity of cyclin-dependent kinases (CDKs) promote progression through the eukaryotic cell cycle. This review examines how proteolysis regulates CDK activity—by degrading CDK activators or inhibitors—and also how proteolysis may directly trigger the transition from metaphase to anaphase. Proteolysis during the cell cycle is mediated by two distinct ubiquitin-conjugation pathways. One pathway, requiring CDC34, initiates DNA replication by degrading a CDK inhibitor. The second pathway, involving a large protein complex called the anaphase-promoting complex or cyclosome, initiates chromosome segregation and exit from mitosis by degrading anaphase inhibitors and mitotic cyclins. Proteolysis therefore drives cell cycle progression not only by regulating CDK activity, but by directly influencing chromosome and spindle dynamics.

Abstract: A method of in situ hybridization for visualizing individual human chromosomes from pter to qter, both in metaphase spreads and interphase nuclei, is reported. DNA inserts from a single chromosomal library are labeled with biotin and partially preannealed with a titrated amount of total human genomic DNA prior to hybridization with cellular or chromosomal preparations. The cross-hybridization of repetitive sequences to nontargeted chromosomes can be markedly suppressed under appropriate preannealing conditions. The remaining single-stranded DNA is hybridized to specimens of interest and detected with fluorescent or enzymelabeled avidin conjugates following post-hybridization washes. DNA inserts from recombinant libraries for chromosomes 1, 4, 7, 8, 13, 14, 18, 20, 21, 22, and X were assessed for their ability to decorate specifically their cognate chromosome; most libraries proved to be highly specific. Quantitative densitometric analyses indicated that the ratio of specific to nonspecific hybridization signal under optimal preannealing conditions was at least 8:1. Interphase nuclei showed a cohesive territorial organization of chromosomal domains, and laserscanning confocal fluorescence microscopy was used to aid the 3-D visualization of these domains. This method should be useful for both karyotypic studies and for the analysis of chromosome topography in interphase cells.

Abstract: Taxol inhibited HeLa cell proliferation by inducing a sustained mitotic block at the metaphase/anaphase boundary. Half-maximal inhibition of cell proliferation occurred at 8 nM taxol, and mitosis was half-maximally blocked at 8 nM taxol. Inhibition of mitosis was associated with formation of an incomplete metaphase plate of chromosomes and an altered arrangement of spindle microtubules that strongly resembled the abnormal organization that occurs with low concentrations of vinblastine and other antimitotic compounds. No increase in microtubule polymer mass occurred below 10 nM taxol. The mass of microtubules increased half-maximally at 80 nM taxol and attained maximal levels (5 times normal) at 330 nM taxol. At submicromolar concentrations, taxol suppressed growing and shortening at the ends of microtubules reassembled in vitro from bovine brain tubulin in a manner that resembled suppression by vinblastine. Taxol was concentrated in HeLa cells several hundredfold to levels that were similar to those which suppressed dynamic instability in vitro. The results indicate that taxol shares a common antiproliferative mechanism with vinblastine. At its lowest effective concentrations, taxol appears to block mitosis by kinetically stabilizing spindle microtubules and not by changing the mass of polymerized microtubules.