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.

Heterochromatinization, chromatin elimination and haploidization in the parahaploid mite Metaseiulus occidentalis (Nesbitt) (Acarina: Phytoseiidae)

Abstract: Embryogenic mitoses, mitoses in females and spermatogenesis are described in the predatory mite Metaseiulus occidentalis (Nesbitt). At 22° C, egg development lasts approximately 4 days. Six chromosomes are seen in mitotic metaphases and anaphases of 0–24 h eggs. Toward the end of this period some embryo squashes have patches of cells containing nuclei which are partially heteropycnotic. These patches of cells apparently increase in size with the age of the embryo. In approximately 1/2 of all 24–48 h-old eggs they encompass all or most cells of the embryo. In these embryos metaphases involved 6 chromosomes, anaphases 3. Either prior to, or following metaphase, a pairing of chromosomes appeared to take place to form 3 units which resembled meiotic diplotene chromosomes where there is opening out between homologues. At metaphase, two sets of 3 chromosomes were slightly differentially stained. One, designated the H set, was darker and slightly more contracted than the other, the E set. At anaphase, 3H and 3E chromosomes segregated in a reductional division retaining the differential contraction until telophase. No cytokinesis appeared. The H set appeared to remain contracted while the E set decontracted to assume the appearance of an interphase nucleus. Both of these entities, side-by-side, created the partially heteropycnotic nucleus mentioned above. The H set then appeared to be excluded from the cell. Mitotic meta and anaphases involving 6 chromosomes were noted in female deutonymphs. Spermatogenesis appeared to encompass an equational division of 3 chromosomes, with the formation of a binucleate spermatid. Two tail structures appeared juxtaposed at the edge of each spermatid and thereafter a separation into two individual sperms occurred. —While mitosis was not studied in known males, we believe that the embryos exhibiting heterochromatinization and elimination of chromosomes in most or all cells were in fact demonstrating parahaploidization.

Analysis of mammalian proteins involved in chromatin modification reveals new metaphase centromeric proteins and distinct chromosomal distribution patterns

Abstract: We have examined the metaphase chromosomal localization of 15 proteins that have previously been described as involved in mammalian chromatin modification and/or transcriptional modulation. Immunofluorescence data indicate that all the proteins localize to human and mouse centromeres, a neocentromere, and the active centromere of a dicentric chromosome, with six of these proteins (Sin3A, PCAF, MYST, MBD2, ORC2, P300/CBP) being demonstrated at mammalian centromeres for the first time. Most of these proteins fall into two distinct chromosomal distribution patterns: (a) kinetochore-associated proteins (Sin3A, PCAF, MYST and BAF180), which colocalize with metaphase kinetochores, but not any of the pericentric and other major heterochromatic regions; and (b) heterochromatin-associated proteins (MeCP2, MBD1, MBD2, ATRX, HP1alpha, HDAC1, HDAC2, DNMT1 and DNMT3b), which colocalize with centromeric/pericentric heterochromatin and all other major heterochromatic sites. A heterogeneous third group (c) consists of the origin recognition complex subunit ORC2 and the histone acetyltransferase P300/CBP, which associate generally with kinetochores in humans and centromeric/pericentric heterochromatin in mouse, with some minor differences in localization. These observations indicate an extensive sharing of protein components involved in chromatin modification at gene loci, centromeres and various chromosomal heterochromatic landmarks. The definition of distinct patterns of chromosomal distribution for these proteins provides a useful basis for the further investigation of the broad-ranging roles of these proteins.

An efficient screening for terminal deletions and translocations of barley chromosomes added to common wheat

Abstract: Summary As a prerequisite to determine physical gene distances in barley chromosomes by deletion mapping, a reliable, fast and inexpensive approach was developed to detect terminal deletions and translocations in individual barley chromosomes added to the chromosome complement of common wheat. A refined fluorescence in situ hybridization (FISH) technique subsequent to N-banding made it possible to detect subtelomeric repeat sequences (HvT01) on all 14 chromosome arms of barley. Some chromosome arms could be distinguished individually based on the number of FISH signals or the intensity of terminal FISH signals. This allowed the detection and selection of deletions and translocations of barley chromosomes (exemplified by 7H and 4HL), which occurred in the progeny of the wheat lines containing a pair of individual barley chromosomes (or telosomes) and a single so-called gametocidal chromosome (2C) of Aegilops cylindrica. This chromosome is known to cause chromosomal breakage in the gametes in which it is absent. Terminal deletions and translocations in barley chromosomes were easily recognized in metaphase and even in interphase nuclei by a decrease in the number of FISH signals specific to the subtelomeric repeat. These aberrations were verified by genomic in situ hybridization. The same approach can be applied to select deletions and translocations of other barley chromosomes in wheat lines that are monosomic for the Ae. cylindrica chromosome 2C.

Suppression of Centromere Dynamics by Taxol® in Living Osteosarcoma Cells

Abstract: Taxol potently blocks mitosis at the transition from metaphase to anaphase, leading to apoptosis in many types of tumor cells. However, the precise mechanism of action of Taxol is not understood. Here we have tested the hypothesis that a primary mechanism of action of Taxol involves suppression of spindle microtubule dynamics. We have used centromere-binding protein B coupled to green fluorescent protein as a marker for the kinetochores and centromeres of chromosomes and analyzed the effects of low Taxol concentrations on the dynamics of centromeres during metaphase of mitosis in living human osteosarcoma (U2OS) cells by quantitative time-lapse confocal microscopy. In the absence of Taxol, the centromere pairs on attached sister chromatids alternately stretch apart and relax back together approximately 1.2 times/min due to tension on the kinetochores produced by the spindle microtubules (referred to here as centromere dynamics). We found that 50-100 nM Taxol significantly suppressed centromere dynamics. For example, Taxol reduced the mean separation distance between the sister centromeres from 0.73 to 0.65 microm, a distance equivalent to that observed in the complete absence of microtubules. The frequency of transitions between stretching and relaxing was also significantly diminished by Taxol (by 27%-35%). The suppressive effects of Taxol on centromere dynamics were associated with maximal accumulation of cells at mitosis (63%), a >90% block of the metaphase/anaphase transition, and complete inhibition of cell proliferation. The data strongly support the idea that the inhibition of centromere dynamics by Taxol prevents silencing of the mitotic spindle surveillance (checkpoint) mechanism. Because Taxol strongly suppresses microtubule dynamics, the data also indicate that centromere dynamics can be accounted for by microtubule dynamics and may not require significant energetic contributions from microtubule motors. The strict correlation between the degree of suppression of centromere dynamics by Taxol and the degree of mitotic block strongly indicates that the primary mechanism responsible for the mitotic block by Taxol in U2OS cells involves suppression of the polymerization dynamics of kinetochore microtubules.