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WormBook : the Online Review of C.... May 2017Sexual reproduction requires the production of haploid gametes (sperm and egg) with only one copy of each chromosome; fertilization then restores the diploid chromosome... (Review)
Review
Sexual reproduction requires the production of haploid gametes (sperm and egg) with only one copy of each chromosome; fertilization then restores the diploid chromosome content in the next generation. This reduction in genetic content is accomplished during a specialized cell division called meiosis, in which two rounds of chromosome segregation follow a single round of DNA replication. In preparation for the first meiotic division, homologous chromosomes pair and synapse, creating a context that promotes formation of crossover recombination events. These crossovers, in conjunction with sister chromatid cohesion, serve to connect the two homologs and facilitate their segregation to opposite poles during the first meiotic division. During the second meiotic division, which is similar to mitosis, sister chromatids separate; the resultant products are haploid cells that become gametes. In Caenorhabditis elegans (and most other eukaryotes) homologous pairing and recombination are required for proper chromosome inheritance during meiosis; accordingly, the events of meiosis are tightly coordinated to ensure the proper execution of these events. In this chapter, we review the seminal events of meiosis: pairing of homologous chromosomes, the changes in chromosome structure that chromosomes undergo during meiosis, the events of meiotic recombination, the differentiation of homologous chromosome pairs into structures optimized for proper chromosome segregation at Meiosis I, and the ultimate segregation of chromosomes during the meiotic divisions. We also review the regulatory processes that ensure the coordinated execution of these meiotic events during prophase I.
Topics: Animals; Caenorhabditis elegans; Cell Division; Chromosome Segregation; Chromosomes; Meiosis; Meiotic Prophase I; Recombination, Genetic
PubMed: 26694509
DOI: 10.1895/wormbook.1.178.1 -
Seminars in Cell & Developmental Biology Sep 2015Meiosis is one of the defining events in gametogenesis. Male and female germ cells both undergo one round of meiotic cell division during their development in order to... (Review)
Review
Meiosis is one of the defining events in gametogenesis. Male and female germ cells both undergo one round of meiotic cell division during their development in order to reduce the ploidy of the gametes, and thereby maintain the ploidy of the species after fertilisation. However, there are some aspects of meiosis in the female germline, such as the prolonged arrest in dictyate, that appear to predispose oocytes to missegregate their chromosomes and transmit aneuploidies to the next generation. These maternally-derived aneuploidies are particularly problematic in humans where they are major contributors to miscarriage, age-related infertility, and the high incidence of Down's syndrome in human conceptions. This review will discuss how events that occur in foetal oocyte development and during the oocytes' prolonged dictyate arrest can influence meiotic chromosome segregation and the incidence of aneuploidy in adult oocytes.
Topics: Animals; Chromosome Segregation; Crossing Over, Genetic; Female; Humans; Meiosis; Oocytes; Oogenesis; Recombination, Genetic; Trisomy
PubMed: 26454098
DOI: 10.1016/j.semcdb.2015.10.005 -
Cold Spring Harbor Perspectives in... May 2015Recombination is a prominent feature of meiosis in which it plays an important role in increasing genetic diversity during inheritance. Additionally, in most organisms,... (Review)
Review
Recombination is a prominent feature of meiosis in which it plays an important role in increasing genetic diversity during inheritance. Additionally, in most organisms, recombination also plays mechanical roles in chromosomal processes, most notably to mediate pairing of homologous chromosomes during prophase and, ultimately, to ensure regular segregation of homologous chromosomes when they separate at the first meiotic division. Recombinational interactions are also subject to important spatial patterning at both early and late stages. Recombination-mediated processes occur in physical and functional linkage with meiotic axial chromosome structure, with interplay in both directions, before, during, and after formation and dissolution of the synaptonemal complex (SC), a highly conserved meiosis-specific structure that links homolog axes along their lengths. These diverse processes also are integrated with recombination-independent interactions between homologous chromosomes, nonhomology-based chromosome couplings/clusterings, and diverse types of chromosome movement. This review provides an overview of these diverse processes and their interrelationships.
Topics: Animals; Chromosome Pairing; Chromosomes; DNA Breaks, Double-Stranded; Humans; Meiosis; Recombination, Genetic; Synaptonemal Complex
PubMed: 25986558
DOI: 10.1101/cshperspect.a016626 -
Genes & Development Mar 2020To induce cell type-specific forms of gene regulation, pioneer factors open tightly packed, inaccessible chromatin sites, enabling the molecular machinery to act on... (Review)
Review
To induce cell type-specific forms of gene regulation, pioneer factors open tightly packed, inaccessible chromatin sites, enabling the molecular machinery to act on functionally significant information encoded in DNA. While previous studies of pioneer factors have revealed their functions in transcriptional regulation, pioneer factors that open chromatin for other physiological events remain undetermined. In this issue of , Spruce and colleagues (pp. 398-412) report the functional significance of a "pioneer complex" in mouse meiotic recombination. This complex, comprised of the zinc finger DNA-binding protein PRDM9 and the SNF2 family chromatin remodeler HELLS, exposes nucleosomal DNA to designate the sites of DNA double-strand breaks that initiate meiotic recombination. Both HELLS and PRDM9 are required for the determination of these recombination hot spots. Through the identification of a pioneer complex for meiotic recombination, this study broadens the conceptual scope of pioneer factors, indicating their functional significance in biological processes beyond transcriptional regulation.
Topics: Animals; DNA Helicases; Histone-Lysine N-Methyltransferase; Meiosis; Mice; Multiprotein Complexes; Nucleosomes; Recombination, Genetic
PubMed: 32122967
DOI: 10.1101/gad.336438.120 -
Comptes Rendus Biologies 2016Meiosis is a specialized cell division at the origin of the haploid cells that eventually develop into the gametes. It therefore lies at the heart of Mendelian heredity.... (Review)
Review
Meiosis is a specialized cell division at the origin of the haploid cells that eventually develop into the gametes. It therefore lies at the heart of Mendelian heredity. Recombination and redistribution of the homologous chromosomes arising during meiosis constitute an important source of genetic diversity, conferring to meiosis a particularly important place in the evolution and the diversification of the species. Our understanding of the molecular mechanisms governing meiotic recombination has considerably progressed these last decades, benefiting from complementary approaches led on various model species. An overview of these mechanisms will be provided as well as a discussion on the implications of these recent discoveries.
Topics: Animals; Chromosome Segregation; Chromosomes; Genetics; Humans; Meiosis; Recombination, Genetic
PubMed: 27180110
DOI: 10.1016/j.crvi.2016.04.003 -
Trends in Genetics : TIG Aug 2021Mutation of the human genome results in three classes of genomic variation: single nucleotide variants; short insertions or deletions; and large structural variants... (Review)
Review
Mutation of the human genome results in three classes of genomic variation: single nucleotide variants; short insertions or deletions; and large structural variants (SVs). Some mutations occur during normal processes, such as meiotic recombination or B cell development, and others result from DNA replication or aberrant repair of breaks in sequence-specific contexts. Regardless of mechanism, mutations are subject to selection, and some hotspots can manifest in disease. Here, we discuss genomic regions prone to mutation, mechanisms contributing to mutation susceptibility, and the processes leading to their accumulation in normal and somatic genomes. With further, more accurate human genome sequencing, additional mutation hotspots, mechanistic details of their formation, and the relevance of hotspots to evolution and disease are likely to be discovered.
Topics: DNA Replication; Genome, Human; Genomic Structural Variation; Genomics; Humans; Mutation; Polymorphism, Single Nucleotide; Recombination, Genetic
PubMed: 33199048
DOI: 10.1016/j.tig.2020.10.003 -
Cells Jun 2023The synaptonemal complex (SC) is a meiosis-specific multiprotein complex that forms between homologous chromosomes during prophase of meiosis I. Upon assembly, the SC... (Review)
Review
The synaptonemal complex (SC) is a meiosis-specific multiprotein complex that forms between homologous chromosomes during prophase of meiosis I. Upon assembly, the SC mediates the synapses of the homologous chromosomes, leading to the formation of bivalents, and physically supports the formation of programmed double-strand breaks (DSBs) and their subsequent repair and maturation into crossovers (COs), which are essential for genome haploidization. Defects in the assembly of the SC or in the function of the associated meiotic recombination machinery can lead to meiotic arrest and human infertility. The majority of proteins and complexes involved in these processes are exclusively expressed during meiosis or harbor meiosis-specific subunits, although some have dual functions in somatic DNA repair and meiosis. Consistent with their functions, aberrant expression and malfunctioning of these genes have been associated with cancer development. In this review, we focus on the significance of the SC and their meiotic-associated proteins in human fertility, as well as how human genetic variants encoding for these proteins affect the meiotic process and contribute to infertility and cancer development.
Topics: Synaptonemal Complex; Humans; Meiosis; Neoplasms; Infertility; Male; Female; Recombination, Genetic
PubMed: 37443752
DOI: 10.3390/cells12131718 -
Philosophical Transactions of the Royal... Oct 2016Meiosis is a key event of sexual life cycles in eukaryotes. Its mechanistic details have been uncovered in several model organisms, and most of its essential features... (Review)
Review
Meiosis is a key event of sexual life cycles in eukaryotes. Its mechanistic details have been uncovered in several model organisms, and most of its essential features have received various and often contradictory evolutionary interpretations. In this perspective, we present an overview of these often 'weird' features. We discuss the origin of meiosis (origin of ploidy reduction and recombination, two-step meiosis), its secondary modifications (in polyploids or asexuals, inverted meiosis), its importance in punctuating life cycles (meiotic arrests, epigenetic resetting, meiotic asymmetry, meiotic fairness) and features associated with recombination (disjunction constraints, heterochiasmy, crossover interference and hotspots). We present the various evolutionary scenarios and selective pressures that have been proposed to account for these features, and we highlight that their evolutionary significance often remains largely mysterious. Resolving these mysteries will likely provide decisive steps towards understanding why sex and recombination are found in the majority of eukaryotes.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.
Topics: Biological Evolution; Eukaryota; Meiosis; Recombination, Genetic; Sex
PubMed: 27619705
DOI: 10.1098/rstb.2016.0001 -
Asian Journal of Andrology 2021Repairing DNA double-strand breaks (DSBs) with homologous chromosomes as templates is the hallmark of meiosis. The critical outcome of meiotic homologous recombination... (Review)
Review
Repairing DNA double-strand breaks (DSBs) with homologous chromosomes as templates is the hallmark of meiosis. The critical outcome of meiotic homologous recombination is crossovers, which ensure faithful chromosome segregation and promote genetic diversity of progenies. Crossover patterns are tightly controlled and exhibit three characteristics: obligatory crossover, crossover interference, and crossover homeostasis. Aberrant crossover patterns are the leading cause of infertility, miscarriage, and congenital disease. Crossover recombination occurs in the context of meiotic chromosomes, and it is tightly integrated with and regulated by meiotic chromosome structure both locally and globally. Meiotic chromosomes are organized in a loop-axis architecture. Diverse evidence shows that chromosome axis length determines crossover frequency. Interestingly, short chromosomes show different crossover patterns compared to long chromosomes. A high frequency of human embryos are aneuploid, primarily derived from female meiosis errors. Dramatically increased aneuploidy in older women is the well-known "maternal age effect." However, a high frequency of aneuploidy also occurs in young women, derived from crossover maturation inefficiency in human females. In addition, frequency of human aneuploidy also shows other age-dependent alterations. Here, current advances in the understanding of these issues are reviewed, regulation of crossover patterns by meiotic chromosomes are discussed, and issues that remain to be investigated are suggested.
Topics: Cell Division; Chromosome Segregation; Humans; Meiosis; Recombination, Genetic
PubMed: 33533735
DOI: 10.4103/aja.aja_86_20 -
Plant Biotechnology Journal Nov 2019In the last 15 years, outstanding progress has been made in understanding the function of meiotic genes in the model dicot and monocot plants Arabidopsis and rice... (Review)
Review
In the last 15 years, outstanding progress has been made in understanding the function of meiotic genes in the model dicot and monocot plants Arabidopsis and rice (Oryza sativa L.), respectively. This knowledge allowed to modulate meiotic recombination in Arabidopsis and, more recently, in rice. For instance, the overall frequency of crossovers (COs) has been stimulated 2.3- and 3.2-fold through the inactivation of the rice FANCM and RECQ4 DNA helicases, respectively, two genes involved in the repair of DNA double-strand breaks (DSBs) as noncrossovers (NCOs) of the Class II crossover pathway. Differently, the programmed induction of DSBs and COs at desired sites is currently explored by guiding the SPO11-1 topoisomerase-like transesterase, initiating meiotic recombination in all eukaryotes, to specific target regions of the rice genome. Furthermore, the inactivation of 3 meiosis-specific genes, namely PAIR1, OsREC8 and OsOSD1, in the Mitosis instead of Meiosis (MiMe) mutant turned rice meiosis into mitosis, thereby abolishing recombination and achieving the first component of apomixis, apomeiosis. The successful translation of Arabidopsis results into a crop further allowed the implementation of two breakthrough strategies that triggered parthenogenesis from the MiMe unreduced clonal egg cell and completed the second component of diplosporous apomixis. Here, we review the most recent advances in and future prospects of the manipulation of meiotic recombination in rice and potentially other major crops, all essential for global food security.
Topics: Arabidopsis; Genes, Plant; Genetic Engineering; Homologous Recombination; Meiosis; Oryza
PubMed: 31199561
DOI: 10.1111/pbi.13189