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.

The disappearance of cyclin B at the end of mitosis is regulated spatially in Drosophila cells.

Abstract: We have followed the behaviour of a cyclin B–green fluorescent protein (GFP) fusion protein in living Drosophila embryos in order to study how the localization and destruction of cyclin B is regulated in space and time We show that the fusion protein accumulates at centrosomes in interphase, in the nucleus in prophase, on the mitotic spindle in prometaphase and on the microtubules that overlap in the middle of the spindle in metaphase In cellularized embryos, toward the end of metaphase, the spindle‐associated cyclin B–GFP disappears from the spindle in a wave that starts at the spindle poles and spreads to the spindle equator; when the cyclin B–GFP on the spindle is almost undetectable, the chromosomes enter anaphase, and any remaining cytoplasmic cyclin B–GFP then disappears over the next few minutes The endogenous cyclin B protein appears to behave in a similar manner These findings suggest that the inactivation of cyclin B is regulated spatially in Drosophila cells We show that the anaphase‐promoting complex/cyclosome (APC/C) specifically interacts with microtubules in embryo extracts, but it is not confined to the spindle in mitosis, suggesting that the spatially regulated disappearance of cyclin B may reflect the spatially regulated activation of the APC/C

Cloned Mice from Fetal Fibroblast Cells Arrested at Metaphase by a Serial Nuclear Transfer

Abstract: Cloning using G(0)-arrested somatic cells has led to the suggestion that this stage of the cell cycle is necessary for the success of cloning. In this study we report that cloned mice can be generated from fetal fibroblasts arrested at metaphase of the cell cycle. The procedure involves fusing a metaphase-arrested fetal fibroblast to an enucleated oocyte. After parthenogenetic activation a polar body and single diploid pronucleus were formed. Some of these were allowed to develop to the blastocyst stage, while others were enucleated and the nucleus was transferred to an enucleated fertilized 1-cell embryo. After the single transfer technique, 2 out of 164 developed to late stages of gestation were dead with gross abnormalities. However, after the serial nuclear transfer, 5 out of 272 embryos were recovered live at Day 19.5, and 2 of these went on to develop into apparently normal adults. All of the cloned embryos showed severe placental hypertrophy and defective differentiation of placental tissues. This study illustrates that reprogramming can occur after nuclear transfer at metaphase of the cell cycle.

Ki-67 detects a nuclear matrix-associated proliferation-related antigen. II. Localization in mitotic cells and association with chromosomes

Abstract: In interphase cells the proliferation-associated antigen recognized by monoclonal antibody Ki-67 is almost exclusively located in the nucleoli. When cells at several stages of mitosis were examined for the localization of the Ki-67 antigen, a striking redistribution could be observed. During prophase the distinct nucleolar Ki-67 fluorescence changed to a bright irregular meshwork throughout the nucleoplasm. At metaphase the antigen appeared to be distributed in a reticulate structure surrounding the condensed chromosomes, while at late telophase a punctated staining of the entire nucleoplasm was observed, which preceded the typical nucleolar localization pattern in each of the two daughter cells. Immunolabelling with Ki-67 of metaphase chromosome spreads revealed a circumferential staining of the individual chromosomes. The Ki-67 antigen is preserved in nuclear matrix preparations obtained after in situ fractionation of interphase cells. When mitotic cells were exposed to such treatments, the obtained fluorescence data suggested that the antigen may be part of the chromosome scaffold. Quantification of the Ki-67 fluorescence signal using flow cytometry revealed the highest staining intensities in mitotic cells. Furthermore, it was shown that nutritionally deprived cells became negative for Ki-67.

SIRT2, a tubulin deacetylase, acts to block the entry to chromosome condensation in response to mitotic stress.

Abstract: We previously identified SIRT2, an nicotinamide adenine dinucleotide (NAD)-dependent tubulin deacetylase, as a protein downregulated in gliomas and glioma cell lines, which are characterized by aneuploidy. Other studies reported SIRT2 to be involved in mitotic progression in the normal cell cycle. We herein investigated whether SIRT2 functions in the mitotic checkpoint in response to mitotic stress caused by microtubule poisons. By monitoring chromosome condensation, the exogenously expressed SIRT2 was found to block the entry to chromosome condensation and subsequent hyperploid cell formation in glioma cell lines with a persistence of the cyclin B/cdc2 activity in response to mitotic stress. SIRT2 is thus a novel mitotic checkpoint protein that functions in the early metaphase to prevent chromosomal instability (CIN), characteristics previously reported for the CHFR protein. We further found that histone deacetylation, but not the aberrant DNA methylation of SIRT2 5'untranslated region is involved in the downregulation of SIRT2. Although SIRT2 is normally exclusively located in the cytoplasm, the rapid accumulation of SIRT2 in the nucleus was observed after treatment with a nuclear export inhibitor, leptomycin B and ionizing radiation in normal human fibroblasts, suggesting that nucleo-cytoplasmic shuttling regulates the SIRT2 function. Collectively, our results suggest that the further study of SIRT2 may thus provide new insights into the relationships among CIN, epigenetic regulation and tumorigenesis.