Metaphase

About: Metaphase is a research topic. Over the lifetime, 6925 publications have been published within this topic receiving 291590 citations. The topic is also known as: GO:0007091 & mitotic metaphase/anaphase transition.

Pre-B cells in mouse bone marrow: immunofluorescence stathmokinetic studies of the proliferation of cytoplasmic mu-chain-bearing cells in normal mice.

Abstract: By using a technique that combines metaphase arrest with immunofluorescence labeling, the proliferation of specifically identified pre-B cells in mouse bone marrow has been analyzed under physiological conditions in vivo. Pre-B cells bearing cytoplasmic mu-chains and no surface mu-chains constituted 12% of marrow nucleated cells, or 27 X 10(5) cells/femur, whereas surface mu-bearing B lymphocytes totaled 33 X 10(5) cells/femur. Pre-B cells measured 7 to 14 micron in diameter, the small number seen in metaphase (1 to 2%) being large cells (greater than 10 microns). After vincristine injection, the metaphase incidence (Imet) of pre-B cells increased with cell size; a broad-dose range of vincristine gave similar Imet values. Mitoses were arrested for 4 hr with no apparent cell death. Linear regression analysis of the increase in Imet of pre-B cells 2 to 4 hr after vincristine revealed a rate of entry into mitosis of 6.3%/hr, relative to all pre-B cells (average compartment turnover time, 16 hr), and 15.3%/hr for the large proliferating pre-B cell subset. This represented a pre-B cell production of 1.3 X 10(5) cells/femoral shaft/hr or 0.5 X 10(8) cells/whole bone marrow organ/day, emphasizing the magnitude of B lymphocyte genesis in normal bone marrow. Combined with reported renewal rates for small pre-B cells and small B lymphocytes, these values form a kinetic model of B lymphocyte development. The results reveal an apparent overproduction of large pre-B cells, consistent with a speculative post-mitotic loss of some immature primary B lymphocytes.

Zinc sparks are triggered by fertilization and facilitate cell cycle resumption in mammalian eggs.

Abstract: In last few hours of maturation, the mouse oocyte takes up over twenty billion zinc atoms and arrests after the first meiotic division, until fertilization or pharmacological intervention stimulates cell cycle progression toward a new embryo. Using chemical and physical probes, we show that fertilization of the mature, zinc-enriched egg triggers the ejection of zinc into the extracellular milieu in a series of coordinated events termed zinc sparks. These events immediately follow the well-established series of calcium oscillations within the activated egg and are evolutionarily conserved in several mammalian species, including rodents and nonhuman primates. Functionally, the zinc sparks mediate a decrease in intracellular zinc content that is necessary for continued cell cycle progression, as increasing zinc levels within the activated egg results in the reestablishment of cell cycle arrest at metaphase. The mammalian egg thus uses a zinc-dependent switch mechanism to toggle between metaphase arrest and r...

Visualization of early chromosome condensation: a hierarchical folding, axial glue model of chromosome structure

Abstract: Current models of mitotic chromosome structure are based largely on the examination of maximally condensed metaphase chromosomes. Here, we test these models by correlating the distribution of two scaffold components with the appearance of prophase chromosome folding intermediates. We confirm an axial distribution of topoisomerase IIα and the condensin subunit, structural maintenance of chromosomes 2 (SMC2), in unextracted metaphase chromosomes, with SMC2 localizing to a 150–200-nm-diameter central core. In contrast to predictions of radial loop/scaffold models, this axial distribution does not appear until late prophase, after formation of uniformly condensed middle prophase chromosomes. Instead, SMC2 associates throughout early and middle prophase chromatids, frequently forming foci over the chromosome exterior. Early prophase condensation occurs through folding of large-scale chromatin fibers into condensed masses. These resolve into linear, 200–300-nm-diameter middle prophase chromatids that double in diameter by late prophase. We propose a unified model of chromosome structure in which hierarchical levels of chromatin folding are stabilized late in mitosis by an axial “glue.”