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 chromokinesin Kid is necessary for chromosome arm orientation and oscillation, but not congression, on mitotic spindles

Abstract: Chromokinesins have been postulated to provide the polar ejection force needed for chromosome congression during mitosis. We have evaluated that possibility by monitoring chromosome movement in vertebrate-cultured cells using time-lapse differential interference contrast microscopy after microinjection with antibodies specific for the chromokinesin Kid. 17.5% of cells injected with Kid-specific antibodies have one or more chromosomes that remain closely opposed to a spindle pole and fail to enter anaphase. In contrast, 82.5% of injected cells align chromosomes in metaphase, progress to anaphase, and display chromosome velocities not significantly different from control cells. However, injected cells lack chromosome oscillations, and chromosome orientation is atypical because chromosome arms extend toward spindle poles during both congression and metaphase. Furthermore, chromosomes cluster into a mass and fail to oscillate when Kid is perturbed in cells containing monopolar spindles. These data indicate that Kid generates the polar ejection force that pushes chromosome arms away from spindle poles in vertebrate-cultured cells. This force increases the efficiency with which chromosomes make bipolar spindle attachments and regulates kinetochore activities necessary for chromosome oscillation, but is not essential for chromosome congression.

Timely anaphase onset requires a novel spindle and kinetochore complex comprising Ska1 and Ska2

Abstract: Chromosome segregation during mitosis requires chromosomes to undergo bipolar attachment on spindle microtubules (MTs) and subsequent silencing of the spindle checkpoint Here, we describe the identification and characterisation of a novel spindle and kinetochore (KT)-associated complex that is required for timely anaphase onset The complex comprises at least two proteins, termed Ska1 (Spindle and KT Associated 1) and Ska2 Ska1 associates with KTs following MT attachment during prometaphase Ska1 and Ska2 interact with each other and Ska1 is required for Ska2 stability in vivo Depletion of either Ska1 or Ska2 by small interfering RNA results in the loss of both proteins from the KT The absence of Ska proteins does not disrupt overall KT structure, but KT fibres show an increased cold-sensitivity Most strikingly, Ska-depleted cells undergo a prolonged checkpoint-dependent delay in a metaphase-like state This delay is characterised by the recruitment of Mad2 protein to a few KTs and the occasional loss of individual chromosomes from the metaphase plate These data suggest that the Ska1/2 complex plays a critical role in the maintenance of the metaphase plate and/or spindle checkpoint silencing

Identification of gains and losses of DNA sequences in primary bladder cancer by comparative genomic hybridization.

Abstract: Comparative genomic hybridization (CGH) makes it possible to detect losses and gains of DNA sequences along all chromosomes in a tumor specimen based on the hybridization of differentially labeled tumor and normal DNA to normal human metaphase chromosomes. In this study, CGH analysis was applied to the identification of genomic imbalances in 26 bladder cancers in order to gain information on the genetic events underlying the development and progression of this malignancy. Losses affecting 11p, 11q, 8p, 9, 17p, 3p, and 12q were all seen in more than 20% of the tumors. The minimal common region of loss in each chromosome was identified based on the analysis of overlapping deletions in different tumors. Gains of DNA sequences were most often found at chromosomal regions distinct from the locations of currently known oncogenes. The bands involved in more than 10% of the tumors were 8q21, 13q21-q34, 1q31, 3q24-q26, and 1p22. In conclusion, these CGH data highlight several previously unreported genetic alterations in bladder cancer. Further detailed studies of these regions with specific molecular genetic techniques may lead to the identification of tumor suppressor genes and oncogenes that play an important role in bladder tumorigenesis.

Preferential binding of a G-quadruplex ligand to human chromosome ends

Abstract: The G-overhangs of telomeres are thought to adopt particular conformations, such as T-loops or G-quadruplexes. It has been suggested that G-quadruplex structures could be stabilized by specific ligands in a new approach to cancer treatment consisting in inhibition of telomerase, an enzyme involved in telomere maintenance and cell immortality. Although the formation of G-quadruplexes was demonstrated in vitro many years ago, it has not been definitively demonstrated in living human cells. We therefore investigated the chromosomal binding of a tritiated G-quadruplex ligand, 3H-360A (2,6-N,N′-methyl-quinolinio-3-yl)-pyridine dicarboxamide [methyl-3H]. We verified the in vitro selectivity of 3H-360A for G-quadruplex structures by equilibrium dialysis. We then showed by binding experiments with human genomic DNA that 3H-360A has a very potent selectivity toward G-quadruplex structures of the telomeric 3′-overhang. Finally, we performed autoradiography of metaphase spreads from cells cultured with 3H-360A. We found that 3H-360A was preferentially bound to chromosome terminal regions of both human normal (peripheral blood lymphocytes) and tumor cells (T98G and CEM1301). In conclusion, our results provide evidence that a specific G-quadruplex ligand interacts with the terminal ends of human chromosomes. They support the hypothesis that G-quadruplex ligands induce and/or stabilize G-quadruplex structures at telomeres of human cells.