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Annual Review of Genetics Nov 2016Meiosis, the mechanism of creating haploid gametes, is a complex cellular process observed across sexually reproducing organisms. Fundamental to meiosis is the process... (Review)
Review
Meiosis, the mechanism of creating haploid gametes, is a complex cellular process observed across sexually reproducing organisms. Fundamental to meiosis is the process of homologous recombination, whereby DNA double-strand breaks are introduced into the genome and are subsequently repaired to generate either noncrossovers or crossovers. Although homologous recombination is essential for chromosome pairing during prophase I, the resulting crossovers are critical for maintaining homolog interactions and enabling accurate segregation at the first meiotic division. Thus, the placement, timing, and frequency of crossover formation must be exquisitely controlled. In this review, we discuss the proteins involved in crossover formation, the process of their formation and designation, and the rules governing crossovers, all within the context of the important landmarks of prophase I. We draw together crossover designation data across organisms, analyze their evolutionary divergence, and propose a universal model for crossover regulation.
Topics: Aneuploidy; Animals; Crossing Over, Genetic; DNA Breaks, Double-Stranded; DNA Repair; Meiosis; Meiotic Prophase I; Protein Processing, Post-Translational; Recombination, Genetic; Synaptonemal Complex
PubMed: 27648641
DOI: 10.1146/annurev-genet-120215-035111 -
Current Genetics Aug 2016The pairing and recombination of homologous chromosomes during the meiotic prophase is necessary for the accurate segregation of chromosomes in meiosis. However, the... (Review)
Review
The pairing and recombination of homologous chromosomes during the meiotic prophase is necessary for the accurate segregation of chromosomes in meiosis. However, the mechanism by which homologous chromosomes achieve this pairing has remained an open question. Meiotic cohesins have been shown to affect chromatin compaction; however, the impact of meiotic cohesins on homologous pairing and the fine structures of cohesion-based chromatin remain to be determined. A recent report using live-cell imaging and super-resolution microscopy demonstrated that the lack of meiotic cohesins alters the chromosome axis structures and impairs the pairing of homologous chromosomes. These results suggest that meiotic cohesin-based chromosome axis structures are crucial for the pairing of homologous chromosomes.
Topics: Cell Cycle Proteins; Chromosomal Proteins, Non-Histone; Chromosome Pairing; Chromosomes, Fungal; Meiosis; Schizosaccharomyces; Cohesins
PubMed: 26856595
DOI: 10.1007/s00294-016-0570-x -
Leukemia Research May 2015Checkpoint with FHA and Ring Finger (CHFR) is a checkpoint protein that reportedly initiates a cell cycle delay in response to microtubule stress during prophase in...
Checkpoint with FHA and Ring Finger (CHFR) is a checkpoint protein that reportedly initiates a cell cycle delay in response to microtubule stress during prophase in mitosis, which has become an interesting target for understanding cancer pathogenesis. Recently, aberrant methylation of the CHFR gene associated with gene silencing has been reported in several cancers. In the present study, we examined the expression of CHFR in B-cell non-Hodgkin lymphoma (B-NHL) in vitro and in vivo. Our results showed that the expression level of CHFR mRNA and protein was reduced in B-NHL tissue samples and B cell lines. Furthermore, CHFR methylation was detected in 39 of 122 B-NHL patients, which was not found in noncancerous reactive hyperplasia of lymph node (RH) tissues. CHFR methylation correlated with the reduced expression of CHFR, high International Prognostic Index (IPI) scores and later pathologic Ann Arbor stages of B-NHL. Treatment with demethylation reagent, 5-Aza-dC, could eliminate the hypermethylation of CHFR, enhance CHFR expression and cell apoptosis and inhibit the cell proliferation of Raji cells, which could be induced by high expression of CHFR in Raji cells. Our results indicated that aberrant methylation of CHFR may be associated with the pathogenesis, progression for B-NHL, which might be a novel molecular marker as prognosis and treatment for B-NHL.
Topics: Adolescent; Adult; Aged; Aged, 80 and over; Cell Cycle Checkpoints; Cell Cycle Proteins; Cell Line, Tumor; Child; Child, Preschool; DNA Methylation; Female; Gene Expression Regulation, Neoplastic; Humans; Lymphoma, B-Cell; Male; Middle Aged; Neoplasm Proteins; Poly-ADP-Ribose Binding Proteins; Prophase; Ubiquitin-Protein Ligases; Young Adult
PubMed: 25798877
DOI: 10.1016/j.leukres.2015.02.007 -
PLoS Genetics Apr 2014Meiotic chromosome segregation relies on homologous chromosomes being linked by at least one crossover, the obligate crossover. Homolog pairing, synapsis and meiosis...
Meiotic chromosome segregation relies on homologous chromosomes being linked by at least one crossover, the obligate crossover. Homolog pairing, synapsis and meiosis specific DNA repair mechanisms are required for crossovers but how they are coordinated to promote the obligate crossover is not well understood. PCH-2 is a highly conserved meiotic AAA+-ATPase that has been assigned a variety of functions; whether these functions reflect its conserved role has been difficult to determine. We show that PCH-2 restrains pairing, synapsis and recombination in C. elegans. Loss of pch-2 results in the acceleration of synapsis and homolog-dependent meiotic DNA repair, producing a subtle increase in meiotic defects, and suppresses pairing, synapsis and recombination defects in some mutant backgrounds. Some defects in pch-2 mutants can be suppressed by incubation at lower temperature and these defects increase in frequency in wildtype worms grown at higher temperature, suggesting that PCH-2 introduces a kinetic barrier to the formation of intermediates that support pairing, synapsis or crossover recombination. We hypothesize that this kinetic barrier contributes to quality control during meiotic prophase. Consistent with this possibility, defects in pch-2 mutants become more severe when another quality control mechanism, germline apoptosis, is abrogated or meiotic DNA repair is mildly disrupted. PCH-2 is expressed in germline nuclei immediately preceding the onset of stable homolog pairing and synapsis. Once chromosomes are synapsed, PCH-2 localizes to the SC and is removed in late pachytene, prior to SC disassembly, correlating with when homolog-dependent DNA repair mechanisms predominate in the germline. Indeed, loss of pch-2 results in premature loss of homolog access. Altogether, our data indicate that PCH-2 coordinates pairing, synapsis and recombination to promote crossover assurance. Specifically, we propose that the conserved function of PCH-2 is to destabilize pairing and/or recombination intermediates to slow their progression and ensure their fidelity during meiotic prophase.
Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Cell Nucleus; Chromosome Pairing; Chromosome Segregation; Chromosomes; Crossing Over, Genetic; DNA Repair; Meiosis; Mutation; Nuclear Proteins; Prophase; Quality Control
PubMed: 24762417
DOI: 10.1371/journal.pgen.1004291 -
The Journal of Cell Biology Apr 1993Earlier results from sectioned nuclei indicating that Schizosaccharomyces pombe does not develop a classical tripartite synaptonemal complex (SC) during meiotic prophase...
Earlier results from sectioned nuclei indicating that Schizosaccharomyces pombe does not develop a classical tripartite synaptonemal complex (SC) during meiotic prophase are confirmed by spreading of whole nuclei. The linear elements appearing during prophase I resemble the axial cores (SC precursors) of other organisms. The number of linear elements in haploid, diploid, and tetraploid strains is always higher than the chromosome number, implying that they are not formed continuously along the chromosomes. Time course experiments reveal that the elements appear after DNA replication and form networks and bundles. Later they separate and approximately 24 individual elements with a total length of 34 microns are observed before degradation and meiotic divisions. Parallel staining of DNA reveals changes in nuclear shape during meiotic prophase. Strains with a mei4 mutation are blocked at a late prophase stage. In serial sections we additionally observed a constant arrangement of the spindle pole body, the nucleolus, and the presumptive centromere cluster. Thus, S. pombe manages to recombine and segregate its chromosomes without SC. This might correlate with the absence of crossover interference. We propose a mechanism for chromosome pairing with initial recognition of the homologs at the centromeres and suggest functions of the linear elements in preparation of the chromosomes for meiosis I disjunction. With the spreading technique combined genetic, molecular, and cytological approaches become feasible in S. pombe. This provides an opportunity to study essential meiotic functions in the absence of SCs which may help to clarify the significance of the SC and its components for meiotic chromosome structure and function.
Topics: Cell Nucleus; Crossing Over, Genetic; Cytological Techniques; Meiosis; Models, Biological; Prophase; Schizosaccharomyces; Synaptonemal Complex
PubMed: 8468345
DOI: 10.1083/jcb.121.2.241 -
Trends in Plant Science Oct 2016The mechanism of cell division has undergone significant alterations during the evolution from aquatic streptophyte algae to land plants. Two new structures evolved, the... (Review)
Review
The mechanism of cell division has undergone significant alterations during the evolution from aquatic streptophyte algae to land plants. Two new structures evolved, the cytokinetic phragmoplast and the preprophase band (PPB) of microtubules, whereas the ancestral mechanism of cleavage and the centrosomes disappeared. We map cell biological data onto the recently emerged phylogenetic tree of streptophytes. The tree suggests that, after the establishment of the phragmoplast mechanism, several groups independently lost their centrosomes. Surprisingly, the phragmoplast shows reductions in the Zygnematophyceae (the sister to land plants), many of which returned to cleavage. The PPB by contrast evolved stepwise and, most likely, originated in the algae. The phragmoplast/PPB mechanism established in this way served as a basis for the 3D development of land plants.
Topics: Biological Evolution; Cell Division; Centrosome; Phylogeny; Plant Physiological Phenomena; Plants; Prophase; Streptophyta
PubMed: 27477927
DOI: 10.1016/j.tplants.2016.07.004 -
PLoS Genetics Oct 2015Chromosome abnormalities are common in the human population, causing germ cell loss at meiotic prophase I and infertility. The mechanisms driving this loss are unknown,...
Chromosome abnormalities are common in the human population, causing germ cell loss at meiotic prophase I and infertility. The mechanisms driving this loss are unknown, but persistent meiotic DNA damage and asynapsis may be triggers. Here we investigate the contribution of these lesions to oocyte elimination in mice with chromosome abnormalities, e.g. Turner syndrome (XO) and translocations. We show that asynapsed chromosomes trigger oocyte elimination at diplonema, which is linked to the presence of phosphorylated H2AFX (γH2AFX). We find that DNA double-strand break (DSB) foci disappear on asynapsed chromosomes during pachynema, excluding persistent DNA damage as a likely cause, and demonstrating the existence in mammalian oocytes of a repair pathway for asynapsis-associated DNA DSBs. Importantly, deletion or point mutation of H2afx restores oocyte numbers in XO females to wild type (XX) levels. Unexpectedly, we find that asynapsed supernumerary chromosomes do not elicit prophase I loss, despite being enriched for γH2AFX and other checkpoint proteins. These results suggest that oocyte loss cannot be explained simply by asynapsis checkpoint models, but is related to the gene content of asynapsed chromosomes. A similar mechanistic basis for oocyte loss may operate in humans with chromosome abnormalities.
Topics: Animals; Chromosome Aberrations; Chromosome Disorders; Chromosome Pairing; DNA Breaks, Double-Stranded; DNA Damage; Female; Histones; Humans; Male; Meiotic Prophase I; Mice; Oocytes; Ovary; Prophase; X Chromosome
PubMed: 26509888
DOI: 10.1371/journal.pgen.1005462 -
Cell Biology International Reports May 1978The action of 5-Fluorodeoxyuridine (FUdR) used as an inhibitor of RNA synthesis on the nucleolar evolution during mitosis, has been studied in meristematic cells. Under...
The action of 5-Fluorodeoxyuridine (FUdR) used as an inhibitor of RNA synthesis on the nucleolar evolution during mitosis, has been studied in meristematic cells. Under FUdR treatment the nucleolar dispersion appears as a continuous process, but generally it is not completed and nucleolar remnants remain throughout the whole mitosis. The nucleolar material which was dispersed is transported by the mitotic chromosomes, and in telophase contributed to the formation of the new nucleolus. The non-dispersed part persisted in the cytoplasm during telophase, coexisting with both the prenucleolar bodies and the new nucleolus which was being formed. Our results suggest the necessity of some kind of RNA synthesis, preferentially blocked by FUdR, for nucleolar dispersion to take place.
Topics: Cell Cycle; Cell Nucleolus; Floxuridine; Plant Cells; Plants; Prophase; Vegetables
PubMed: 149595
DOI: 10.1016/0309-1651(78)90003-6 -
Biological Research 2012We analyzed the in vitro effects of the anti-tumoral drugs doxorubicin, cytosine arabinoside and hydroxyurea on the G2-prophase checkpoint in lymphocytes from healthy...
We analyzed the in vitro effects of the anti-tumoral drugs doxorubicin, cytosine arabinoside and hydroxyurea on the G2-prophase checkpoint in lymphocytes from healthy individuals. At biologically equivalent concentrations, the induced DNA damage activated the corresponding checkpoint. Thus: i) there was a concentration-dependent delay of G2 time and an increase of both the total DNA lesions produced and repaired before metaphase and; ii) G2-checkpoint adaptation took place as chromosome aberrations (CAs) started to appear in the metaphase, indicating the presence of unrepaired double-strand breaks (DSBs) in the previous G2. The checkpoint ATM/ATR kinases are involved in DSB repair, since the recorded frequency of CAs increased when both kinases were caffeine-abrogated. In genotoxic-treated cells about three-fold higher repair activity was observed in relation to the endogenous background level of DNA lesions. The maximum rate of DNA repaired was 3.4 CAs/100 metaphases/hour, this rise being accompanied by a modest 1.3 fold lengthening of late G2 prophase timing. Because of mitotic chromosome condensation, no DSBs repair can take place until the G1 phase of the next cell cycle, when it occurs by DNA non-homologous end joining (NHEJ). Chromosomal rearrangements formed as a consequence of these error-prone DSB repairs ensure the development of genome instability through the DNA-fusion-bridge cycle. Hence, adaptation of the G2 checkpoint supports the appearance of secondary neoplasia in patients pretreated with genotoxic drugs.
Topics: Adult; Antibiotics, Antineoplastic; Chromosome Aberrations; Cytarabine; DNA Damage; Doxorubicin; Female; G2 Phase Cell Cycle Checkpoints; Humans; Hydroxyurea; Lymphocytes; Male; Prophase; Young Adult
PubMed: 23096362
DOI: 10.4067/S0716-97602012000200010 -
Journal of Visualized Experiments : JoVE Feb 2018Chromatin spread techniques have been widely used to assess the dynamic localization of various proteins during gametogenesis, particularly for spermatogenesis. These...
Chromatin spread techniques have been widely used to assess the dynamic localization of various proteins during gametogenesis, particularly for spermatogenesis. These techniques allow for visualization of protein and DNA localization patterns during meiotic events such as homologous chromosome pairing, synapsis and DNA repair. While a few protocols have been described in the literature, general chromatin spread techniques using mammalian prophase oocytes are limited and difficult due to the timing of meiosis initiation in fetal ovaries. In comparison, prophase spermatocytes can be collected from juvenile male mice with higher yields without the need for microdissection. However, it is difficult to obtain a pure synchronized population of cells at specific stages due to the heterogeneity of meiotic and post-meiotic germ cell populations in the juvenile and adult testis. For later stages of meiosis, it is advantageous to assess oocytes undergoing meiosis I (MI) or meiosis II (MII), because groups of mature oocytes can be collected from adult female mice and stimulated to resume meiosis in culture. Here, methods for meiotic chromatin spread preparations using oocytes dissected from fetal, neonatal and adult ovaries are described with accompanying video demonstrations. Chromosome missegregation events in mammalian oocytes are frequent, particularly during MI. These techniques can be used to assess and characterize the effects of different mutations or environmental exposures during various stages of oogenesis. As there are distinct differences between oogenesis and spermatogenesis, the techniques described within are invaluable to increase our understanding of mammalian oogenesis and the sexually dimorphic features of chromosome and protein dynamics during meiosis.
Topics: Animals; Chromatin; Female; Metaphase; Mice; Oocytes; Pregnancy; Prophase
PubMed: 29553540
DOI: 10.3791/56736