Topic
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.
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TL;DR: The results suggest that radiation-induced G2-phase block is associated with unrejoined chromosome fragments induced by radiation exposure during G0, and chromosomal exchanges was similar in G0 (after repair), G2 and M phase for cells exposed to X rays, while a lower frequency of exchanges was observed in M phase when lymphocytes were irradiated with high-LET carbon ions.
Abstract: We have studied the induction of chromosomal aberrations in human lymphocytes exposed in G0 to X rays or carbon ions. Aberrations were analyzed in G0, G1, G2 or M phase. Analysis during the interphase was performed by chemically induced premature chromosome condensation, which allows scoring of aberrations in G1, G2 and M phase; fusion-induced premature chromosome condensation was used to analyze the damage in G0 cells after incubation for repair; M-phase cells were obtained by conventional Colcemid block. Aberrations were scored by Giemsa staining or fluorescence in situ hybridization (chromosomes 2 and 4). Similar yields of fragments were observed in G1 and G2 phase, but lower yields were scored in metaphase. The frequency of chromosomal exchanges was similar in G0 (after repair), G2 and M phase for cells exposed to X rays, while a lower frequency of exchanges was observed in M phase when lymphocytes were irradiated with high-LET carbon ions. The results suggest that radiation-induced G2-phase block is associated with unrejoined chromosome fragments induced by radiation exposure during G0.
82 citations
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TL;DR: Giemsa techniques have refused to reveal G-banding patterns in plant chromosomes, but the striking correspondence of pachytene chromomeres and mitotic G-bands in higher vertebrates suggests that pachyTene chromomes are G- band equivalents, and that this may also be the case in plants.
Abstract: Giemsa techniques have refused to reveal G-banding patterns in plant chromosomes. Whatever has been differentially stained so far in plant chromosomes by various techniques represents constitutive heterochromatin (redefined in this paper). Patterns of this type must not be confused with the G-banding patterns of higher vertebrates which reveal an additional chromosome segmentation beyond that due to constitutive heterochromatin. The absence of G-bands in plants is explained as follows: 1) Plant chromosomes in metaphase contain much more DNA than G-banding vertebrate chromosomes of comparable length. At such a high degree of contraction vertebrate chromosomes too would not show G-bands, simply for optical reasons. 2) The striking correspondence of pachytene chromomeres and mitotic G-bands in higher vertebrates suggests that pachytene chromomeres are G-band equivalents, and that this may also be the case in plants. G-banded vertebrate chromosomes are on the average only 2.3 times shorter in mitosis than in pachytene; the chromomeric pattern therefore still can be shown. In contrast, plant chromosomes are approximately 10 times shorter at mitotic metaphase; their pachytene-like arrangement of chromomeres is therefore no longer demonstrable.
82 citations
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TL;DR: Observations indicate that centrosomes eject particles of Cnn-containing pericentriolar material that move on dynamic astral microtubules at a rate that varies with the cell cycle, and propose that flare particles play a role in organizing the actin cytoskeleton during syncytial cleavage.
Abstract: The Drosophila Centrosomin (Cnn) protein is an essential core
component of centrosomes in the early embryo. We have expressed a Cnn-GFP
fusion construct in cleavage stage embryos, which rescues the maternal effect
lethality of cnn mutant animals. The localization patterns seen with
GFP-Cnn are identical to the patterns we see by immunofluorescent staining
with anti-Cnn antibodies. Live imaging of centrosomes with Cnn-GFP reveals
surprisingly dynamic features of the centrosome. Extracentrosomal particles of
Cnn move radially from the centrosome and frequently change their direction.
D-TACC colocalized with Cnn at these particles. We have named these extrusions
`flares9. Flares are dependent on microtubules, since disruption of the
microtubule array severs the movement of these particles. Movement of flare
particles is cleavage-cycle-dependent and appears to be attributed mostly to
their association with dynamic astral microtubules. Flare activity decreases
at metaphase, then increases at telophase and remains at this higher level of
activity until the next metaphase. Flares appear to be similar to vertebrate
PCM-1-containing `centriolar satellites9 in their behavior. By injecting
rhodamine-actin, we observed that flares extend no farther than the actin
cage. Additionally, disruption of the microfilament array increased the extent
of flare movement. These observations indicate that centrosomes eject
particles of Cnn-containing pericentriolar material that move on dynamic
astral microtubules at a rate that varies with the cell cycle. We propose that
flare particles play a role in organizing the actin cytoskeleton during
syncytial cleavage.
82 citations
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TL;DR: Results indicate that exposure to alpha-tocopherol or L-ascorbic acid promotes the development of porcine DOs from MI to MII and prevents cumulus cell DNA fragmentation at certain levels.
Abstract: It is known that alpha-tocopherol (vitamin E) and L-ascorbic acid (vitamin C) can modulate many biochemical processes intracellularly or extracellularly as antioxidants. The objective of the present study was to investigate the effects of alpha-tocopherol and L-ascorbic acid on porcine oocyte meiotic maturation, viability and the functions of cumulus cells. In two independent experiments, porcine oocytes with or free from cumulus cells were exposed to different levels of alpha-tocopherol (0, 10, 100 and 200 microM) or L-ascorbic acid (0, 50, 250 and 750 microM). Cumulus expansion, cumulus cell DNA fragmentation, meiotic maturation and degeneration of oocytes were assessed 48 h after in vitro culture. The results showed that: (1) neither alpha-tocopherol nor L-ascorbic acid influenced cumulus expansion but both prevented cumulus cell DNA fragmentation. (2) Alpha-tocopherol lowered the percentage of denuded oocytes (DOs) arrested at germinal vesicle stage (GV). Among the oocytes undergoing germinal vesicle breakdown (GVBD) proportion, fewer DOs treated by alpha-tocopherol were at metaphase I (MI) and more at metaphase II (MII). L-ascorbic acid caused lower percentage of DOs arrested at GV stage and higher percentage of DOs undergoing GVBD, especially at MII. The influences of alpha-tocopherol and L-ascorbic acid were not obvious in cumulus-enclosed oocytes (CEOs). (3) Both vitamins compromised the viability of CEOs and DOs. These results indicate that exposure to alpha-tocopherol or L-ascorbic acid promotes the development of porcine DOs from MI to MII and prevents cumulus cell DNA fragmentation at certain levels, especially 10 microM alpha-tocopherol or 250 microM L-ascorbic acid.
82 citations
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TL;DR: It is suggested that distinct from its role in chromosome movement, Kid contributes to spindle morphogenesis by mediating spindle microtubules stabilization.
Abstract: The human chromokinesin Kid/kinesin-10, a plus end-directed microtubule (MT)-based motor with both microtubule- and DNA-binding domains, is required for proper chromosome alignment at the metaphase plate. Here, we performed RNA interference experiments to deplete endogenous Kid from HeLa cells and confirmed defects in metaphase chromosome arm alignment in Kid-depleted cells. In addition, we noted a shortening of the spindle length, resulting in a pole-to-pole distance only 80% of wild type. The spindle microtubule-bundles with which Kid normally colocalize became less robust. Rescue of the two Kid deficiency phenotypes-imprecise chromosome alignment at metaphase and shortened spindles- exhibited distinct requirements. Mutants lacking either the DNA-binding domain or the MT motor ATPase failed to rescue the former defect, whereas rescue of the shortened spindle phenotype required neither activity. Kid also exhibits microtubule bundling activity in vitro, and rescue of the shortened spindle phenotype and the bundling activity displayed similar domain requirements, except that rescue required a coiled-coil domain not needed for bundling. These results suggest that distinct from its role in chromosome movement, Kid contributes to spindle morphogenesis by mediating spindle microtubules stabilization.
82 citations