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.

Phenotypic Analysis of Separation-of-Function Alleles of MEI-41, Drosophila ATM/ATR

Abstract: ATM/ATR kinases act as signal transducers in eukaryotic DNA damage and replication checkpoints. Mutations in ATM/ATR homologs have pleiotropic effects that range from sterility to increased killing by genotoxins in humans, mice, and Drosophila. Here we report the generation of a null allele of mei-41, Drosophila ATM/ATR homolog, and the use of it to document a semidominant effect on a larval mitotic checkpoint and methyl methanesulfonate (MMS) sensitivity. We also tested the role of mei-41 in a recently characterized checkpoint that delays metaphase/anaphase transition after DNA damage in cellular embryos. We then compare five existing mei-41 alleles to the null with respect to known phenotypes (female sterility, cell cycle checkpoints, and MMS resistance). We find that not all phenotypes are affected equally by each allele, i.e., the functions of MEI-41 in ensuring fertility, cell cycle regulation, and resistance to genotoxins are genetically separable. We propose that MEI-41 acts not in a single rigid signal transduction pathway, but in multiple molecular contexts to carry out its many functions. Sequence analysis identified mutations, which, for most alleles, fall in the poorly characterized region outside the kinase domain; this allowed us to tentatively identify additional functional domains of MEI-41 that could be subjected to future structure-function studies of this key molecule.

Indications of centromere movement during interphase and differentiation.

Abstract: Mouse and human DNA sequences from centromeric and ribosomal domains were labeled with biotinylated deoxynucleotides and hybridized in situ to paraformaldehyde-fixed tissue culture cells. Centromeres were widely dispersed in most of these interphase nuclei. At late G2 phases of the cell cycle, centromeres appeared to coalesce and then to align in an orderly pattern, with discrete positional assignments for individuals chromosomes in metaphase and anaphase. Ribosomal cistrons were also organized in an orderly and defined fashion during mitosis. As soon as the nuclear membrane forms in early G1, centromeres rapidly disperse throughout the nucleus. Centromere patterns during G1 and S were indistinguishable in cultured cells, as determined by double-labeling experiments. Antibodies that bind to centric chromosomal proteins revealed the same patterns in cultured cells as those obtained with DNA sequence-specific probes. Large differentiated neurons display reproducible collections of centromeres in interphase that are very different from those seen in cultured cells. Neurons in widely divergent mammalian species, despite large differences in centromeric DNA sequences, maintain similar nuclear positions for these chromosomal segments. Similarly, ribosomal cistrons are positioned in comparable nuclear locales in neurons of divergent species. It is suggested that such arrangements reflect, or are necessary for, the function of a given cell type. Studies of large cerebellar neurons at critical times in development indicated a relative "movement" of centromeric domains, away from the nuclear membrane and toward the central nucleolar region. It is possible that the orderly and temporal positioning of centromeric, as well as of other chromosomal regions, is based on protein-nucleic acid interactions. Implications for trisomy 21 and other disorders involving chromosomal rearrangements, such as transposition, are considered from this perspective.

Mammalian cells change volume during mitosis.

Abstract: Using single cell-imaging methods we have found that the volume of adherent cells grown in culture decreases as the cells rounds when it enters mitosis. A minimal volume is reached at metaphase. Rapid volume recovery initiates before abscission as cells make the transition from metaphase to cytokinesis. These volume changes are simultaneous with the rapid surface area decrease and recovery observed in mitotic cells [1].

Untangling the role of DNA topoisomerase II in mitotic chromosome structure and function

Abstract: DNA topoisomerase II (topo II) is involved in chromosome structure and function, although its exact location and role in mitosis are somewhat controversial. This is due in part to the varied reports of its localization on mitotic chromosomes, which has been described at different times as uniformly distributed, axial on the chromosome arms and predominantly centromeric. These disparate results are probably due to several factors, including use of different preparation and fixation techniques, species differences and changes in distribution during the cell cycle. Recently, several papers have re-investigated the distribution of topo II on chromosomes as a function of cell cycle and species(1-3). The new studies suggest that Topo II has a dynamic pattern of distribution on the chromosomes, in general becoming axial as chromosomes condense during prophase and then concentrating at centromeres during metaphase. These experiments suggest a novel role for topo II in centromere structure and function.