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.

Shaping mitotic chromosomes: From classical concepts to molecular mechanisms.

Abstract: How eukaryotic genomes are packaged into compact cylindrical chromosomes in preparation for cell divisions has remained one of the major unsolved questions of cell biology. Novel approaches to study the topology of DNA helices inside the nuclei of intact cells, paired with computational modeling and precise biomechanical measurements of isolated chromosomes, have advanced our understanding of mitotic chromosome architecture. In this Review Essay, we discuss – in light of these recent insights – the role of chromatin architecture and the functions and possible mechanisms of SMC protein complexes and other molecular machines in the formation of mitotic chromosomes. Based on the information available, we propose a stepwise model of mitotic chromosome condensation that envisions the sequential generation of intra-chromosomal linkages by condensin complexes in the context of cohesin-mediated inter-chromosomal linkages, assisted by topoisomerase II. The described scenario results in rod-shaped metaphase chromosomes ready for their segregation to the cell poles.

Detection of the t(2;13)(q35;q14) and PAX3‐FKHR fusion in alveolar rhabdomyosarcoma by fluorescence in situ hybridization

Abstract: Cytogenetic studies of the pediatric solid tumor alveolar rhabdomyosarcoma have demonstrated the presence of a consistent chromosomal translocation, t(2;13)(q35;q14). We recently identified PAX3 and FKHR as the genes on chromosomes 2 and 13, respectively, that are juxtaposed by this translocation. As one means of detecting the t(2;13) translocation in clinical specimens, we have developed a fluorescence in situ hybridization (FISH) assay that may be used for both interphase and metaphase cells. Translocation of the 5' region of the FKHR gene to the derivative chromosome 2, and retention of the 3' region of FKHR on the derivative chromosome 13 [(der(13)], were demonstrated in metaphase cells from a rhabdomyosarcoma cell line with a previously identified t(2;13) translocation. A 5' PAX3 cosmid probe was shown to localize to 2q35 in normal cells, and to translocate to the der(13) in the rhabdomyosarcoma cell line. In order to detect the der(13) in interphase nuclei, we labeled the 3'FKHR and the 5'PAX3 cosmid probes with digoxigenin and biotin, respectively, and used these in a two-color FISH assay. The presence of the der(13) was visualized as juxtaposed or overlapping red and green signals in metaphase and interphase tumor cells. The PAX3-FKHR FISH assay was then applied to a series of cytogenetically characterized pediatric sarcoma cell lines. The presence of the der(13) was demonstrated by FISH in all cases containing a cytogenetically detectable t(2;13). The FISH assay was then applied to a series of 20 embryonal and alveolar rhabdomyosarcoma samples. All 10 of the alveolar rhabdomyosarcoma specimens demonstrated a der(13) with the FISH assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Centromere localization at meiosis and the position of chiasmata in the male and female mouse.

Abstract: Techniques for obtaining differential Giemsa staining of the paracentromeric (p.c.) regions of male and female mouse meiotic chromosomes (centromeric heterochromatin) were explored and standard procedures developed for the different meiotic cells in the two sexes. The best result followed the use of heat at controlled pH in Sorensen's phosphate buffer or in Standard Saline Citrate (SSC) solutions. With these techniques, morphological features of the p.c. regions and their variation were studied in normal animals (CFLP strain) and in a strain (AKR) homozygous for a centric fusion [T(11; ?)-1 Ald] between chromosomes No. 6 and No. 15 (Miller et al., 1971). The Y chromosome was often found to show distinct p. c. staining at first and apparently at second meiotic metaphase, and the X and Y chromosomes were found to associate as bivalents by their long arms. Autosomal p.c. regions showed variation in size which might indicate differences between non-homologous chromosomes but a tendency to similarity between homologues. Differences were found between males and females in respect to proportions and variation of bivalents with single and double chiasmata. The relative positions of chiasmata were different in the two sexes. The presence of the centric fusion in the males did not seem to affect the pairing behaviour of the remaining autosomes or of those taking part in the centric fusion. The possibility is discussed that the p.c. regions, to which also other functions would seem to appertain, may be important for chromosome recognition and pairing, possibly on a quantitative basis.

Premature dyad separation in meiosis II is the major segregation error with maternal age in mouse oocytes

Abstract: As women get older their oocytes become susceptible to chromosome mis-segregation. This generates aneuploid embryos, leading to increased infertility and birth defects. Here we examined the provenance of aneuploidy by tracking chromosomes and their kinetochores in oocytes from young and aged mice. Changes consistent with chromosome cohesion deterioration were found with age, including increased interkinetochore distance and loss of the centromeric protector of cohesion SGO2 in metaphase II arrested (metII) eggs, as well as a rise in the number of weakly attached bivalents in meiosis I (MI) and lagging chromosomes at anaphase I. However, there were no MI errors in congression or biorientation. Instead, premature separation of dyads in meiosis II was the major segregation defect in aged eggs and these were associated with very low levels of SGO2. These data show that although considerable cohesion loss occurs during MI, its consequences are observed during meiosis II, when centromeric cohesion is needed to maintain dyad integrity.

Treatment of Vicia faba root tip cells with specific inhibitors to cyclin‐dependent kinases leads to abnormal spindle formation

Abstract: Many events during cell division are triggered by an evolutionary conserved regulator, the cyclin-dependent kinase (Cdk). Here we used two novel drugs, the purine analogues bohemine and roscovitine, to study the role of Cdks in cell cycle progression and microtubule organisation in Vicia faba root tip cells. Both drugs inhibited the activity of immunopurified Vicia faba and alfalfa Cdc2-kinase. The transcript levels of an A- and B-type cyclin, as well as of the cdc2 genes, declined in treated root tips, while the mRNA level of a D-type cyclin gene was not affected. An observed transient arrest at the G1/S and G2/M regulatory points indicated that inhibition of the Cdc2-kinase had an effect on both transitions. In contrast to the regular bipolar spindle in untreated cell, in drug-treated metaphase cells abnormally short and dense kinetochore microtubule fibres were observed. These microtubules were randomly arranged in the vicinity of the kinetochores and connected the chromosomes. Thus, the chromosomes were not aligned on the metaphase plate but were arranged in a circle, with kinetochores pointing inwards and chromosome arms pointing outwards. gamma-Tubulin, which plays a role in microtubule nucleation, also localised to the centre of the monopolar spindle. The observed abnormalities in mitosis, after inhibition of Cdc2-kinase by specific drugs, suggest a role for this enzyme in regulating some of the steps leading to a bipolar spindle structure.