Mitosis mammalian cells

Downes CS, Mullinger AM, Johnson RT 1991 Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis. Proc Nad Acad Sci USA 88 8895-8899... 

Barber CM et al., report that histone H2A is highly phosphorylated at Serine 1 residues during mitosis in the worm, fly, and mammalian cells (Barber et al, 2004). This phosphorylation by MSKl negatively regulated transcription on chromatin templates (Zhang et al, 2004). 

Mammalian cells in vitro are exposed to the test chemical with and without an exogenous mammalian metaboUc activation system and cultured for two rounds of replication in bromodeox3Uiridine (BrdU) containing medium. After treatment with a spindle inhibitor (e.g., colchicine) to accumulate cells in a metaphase-Uke stage of mitosis (c-metaphase), cells are harvested, stained, and metaphase cells analyzed for SCEs. Primary cultures (e.g., human lymphocytes) or established cell lines (e.g., Chinese hamster ovary or lung cells) may be used in the assay. At least three adequately spaced concentrations of the test substance should be used. 

The simplest and most sensitive assays for detecting clastogenic (i.e. chromosomal breaking) effects involve the use of mammalian cells. Cultures of established cell lines (e.g. Chinese hamster ovary) as well as primary cell cultures (e.g. human l)nnphocyte) may be used. After exposure to a range of chemical concentrations in the presence and absence of an appropriate metabolic activation system, the cell cultures are treated with a spindle inhibitor (e.g. vinblastine) to accumulate cells in a metaphaselike stage of mitosis. Cells are harvested at appropriate times and chromosome preparations are made, stained with DNA-specific dye and the metaphase cells are analysed under the microscope for chromosome abnormalities. 

The vinca alkaloids bind avidly to tubulin, a class of proteins that form the mitotic spindle during cell division. The drugs cause cellular arrest in metaphase during mitosis, and cell division cannot be completed. Although the vinca alkaloids usually have been regarded as phase specific in the cell cycle, some mammalian cells are most vulnerable in the late S-phase. 

Onfelt, A. (1987) Spindle disturbances in mammalian cells. III. Toxicity, c-mitosis and aneuploidy with 22 different compounds. Specific and unspecific mechanisms. Mutat. Res., 182,135-154... 

Cell division also requires duplication of the protein mass and of organelles, which takes longer to be accomplished than DNA replication. Thus, for the cell to be able to grow and duplicate its contents, there are two additional phases in the cell cycle the Gi phase (between the M and the S phase), and the G2 phase (between the S-phase and mitosis). The cell cycle is divided into four sequential phases Gi, S, G2, and M (Figure 7.2). The part of the cycle that consists of phases Gi, S, and G2 is designated the interphase. In a typical proliferating mammalian cell, the interphase can... 

Chapter 10) has been shown to be remarkably similar to that of mammalian cells during interphase and mitosis (719). 

Most of the information concerning recombination between repeated sequences has been derived from studies in the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe,5 although some classes of ectopic recombination have also been studied in mammalian cells.6 The yeast studies indicate that the rates of ectopic recombination are surprisingly high (similar to the rates of classical recombination) and that the rates of these events are much higher in meiosis than in mitosis. Conversion events involving repeats on nonhomologous chromosomes are associated... 

This in vitro cytogenetic test is a clastogenicity test system for the detection of chromosomal aberrations in cultured mammalian cells or primary cultures. Chromosomal aberrations may be either structural or numerical. However, because cytogenetic assays are usually designed to analyze cells at their first posttreatment mitosis and numerical aberrations require at least one cell division to be visualized, this type of aberration is generally not observed in a routine cytogenetic assay. The best estimate of aberration frequency is the first cell division after the start of treatment. Structural aberrations are of two types chromosome or chromatid aberrations. 

The inner nuclear membrane of the nucleus in mammalian cells is supported by a network of intermediate filaments called the nuclear lamina which is comprised of lamins. In late prophase of mitosis, the nuclear membrane fragments into vesicles triggered largely by phosphorylation of the lamins at various serine residues. This serves to disassemble the nuclear lamina. At the completion of mitosis, dephosphorylation of the lamins allows the vesicles in each of the new daughter cells to reform nuclear membranes surrounding the chromosomes. 

DNA in mammalian cells is organized in complex structures called chromosomes (prokaryotes do not have a nucleus, do not divide by mitosis, and do not, strictly speaking, have chromosomes). The DNA in the chromosomes of human and other eukaryotic cells is intimately associated with two classes of proteins called histones and nonhistones. Collectively, DNA, histones, and nonhistones constitute chromatin, from which the name chromosome is derived. The DNA in a chromosome is an extremely long, linear molecule that must be condensed and organized to fit into the chromosomes in the nucleus. (The DNA in the 46 human chromosomes would be about 1 m long if fully extended.) Histones are responsible for the structural organization of DNA in chromosomes the nonhistone proteins... 

Figure 34.1 Motion within cells. This high-voltage electron micrograph shows the mitotic apparatus in a metaphase mammalian cell. The targe cylindrical objects are chromosomes, and the threadlike structures stretched across the center are microtubules—tracks for the molecular motors that move chromosomes. Many processes, including chromosome segregation in mitosis, depend on the action of molecular-motor proteins.. [Courtesy of Dr. J. R. McIntosh.]...

The first evidence that diffusible factors regulate the cell cycle came from cell-fusion experiments with cultured mammalian cells. When interphase cells in the Gi, S, or G2 phase of the cell cycle were fused to cells in mitosis, their nuclear envelopes retracted and their chromosomes condensed (Figure 21-3). This finding indicates that some diffusible component or components in the cytoplasm of the mitotic cells forced interphase nuclei to undergo many of the processes associated with early mitosis. We now know that these factors are the mitotic cyclin-CDK complexes. 

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