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Science Advances Oct 2023In almost all sexually reproducing organisms, meiotic recombination and cell division require the synapsis of homologous chromosomes by a large proteinaceous structure,...
In almost all sexually reproducing organisms, meiotic recombination and cell division require the synapsis of homologous chromosomes by a large proteinaceous structure, the synaptonemal complex (SC). While the SC's overall structure is highly conserved across eukaryotes, its constituent proteins diverge between phyla. Transverse filament protein, SYCP1, spans the width of the SC and undergoes amino-terminal head-to-head self-assembly in vitro through a motif that is unusually highly conserved across kingdoms of life. Here, we report creation of mouse mutants, and , that target SYCP1's head-to-head interface. L106E resulted in a complete loss of synapsis, while L102E had no apparent effect on synapsis, in agreement with their differential effects on the SYCP1 head-to-head interface in molecular dynamics simulations. In mice, homologs aligned and recruited low levels of mutant SYCP1 and other SC proteins, but the absence of synapsis led to failure of crossover formation and meiotic arrest. We conclude that SYCP1's conserved head-to-head interface is essential for meiotic chromosome synapsis in vivo.
Topics: Animals; Mice; Chromosome Pairing; Homologous Recombination; Meiosis; Nuclear Proteins; Synaptonemal Complex
PubMed: 37862414
DOI: 10.1126/sciadv.adi1562 -
International Journal of Molecular... Aug 2022Meiosis initiates with the formation of double strand breaks (DSBs) throughout the genome. To avoid genomic instability, these DSBs need to be correctly repaired by...
Meiosis initiates with the formation of double strand breaks (DSBs) throughout the genome. To avoid genomic instability, these DSBs need to be correctly repaired by homologous recombination. Surveillance mechanisms involving the DNA damage response (DDR) pathway ATM-CHK2-p53 can detect the persistence of unrepaired DBSs and activate the recombination-dependent arrest at the pachytene stage. However, a complete understanding of p53 functions under normal physiological conditions remains lacking. Here, we report a detailed analysis of the p53 role during meiotic prophase in mice spermatocytes. We show that the absence of p53 regulates prophase progression by slowing down the pachytene stage when the recombination-dependent arrest occurs. Furthermore, our results show that p53 is necessary for proper crossover (CO) formation and localization. Our study contributes to a deeper understanding of p53 roles during the meiotic prophase.
Topics: Animals; Cell Cycle Proteins; DNA Breaks, Double-Stranded; Male; Meiosis; Mice; Prophase; Spermatocytes; Tumor Suppressor Protein p53
PubMed: 36077210
DOI: 10.3390/ijms23179818 -
Nucleus (Austin, Tex.) Dec 2019Active meiotic chromosome movements are a universally conserved feature. They occur at the early stages of prophase of the first meiotic division and support the... (Review)
Review
Active meiotic chromosome movements are a universally conserved feature. They occur at the early stages of prophase of the first meiotic division and support the chromosome pairing process by (1) efficiently installing the synaptonemal complex between homologous chromosomes, (2) discouraging inadvertent chromosome interactions and (3) bringing homologous chromosomes into proximity. Chromosome movements are driven by forces in the cytoplasm, which are passed on to chromosome ends attached to the nuclear periphery by nuclear-membrane-spanning protein modules. In this extra view, we highlight our recent studies into the role of the nuclear lamina during this process to emphasize that it is a highly conserved structure in metazoans. The nuclear lamina forms a rigid proteinaceous network that underlies the inner nuclear membrane to provide stability to the nucleus. Misdemeanors of the nuclear lamina during meiosis has deleterious consequences for the viability and health of the offspring, highlighting the importance of a functional nuclear lamina during this cell cycle stage. Abbreviations: DSB: DNA double strand break; LEM: LAP2, Emerin, MAN1; LINC: LInker of the Nucleoskeleton and Cytoskeleton; RPM: rapid prophase movement; SUN/KASH: Sad1p, UNC-84/Klarsicht, ANC-1, Syne Homology.
Topics: Animals; Chromosomes; Humans; Lamins; Meiosis
PubMed: 30676220
DOI: 10.1080/19491034.2019.1572413 -
Frontiers in Endocrinology 2023The non-growing, meiotically-arrested oocytes housed within primordial follicles are exquisitely sensitive to genotoxic insults from endogenous and exogenous sources....
INTRODUCTION
The non-growing, meiotically-arrested oocytes housed within primordial follicles are exquisitely sensitive to genotoxic insults from endogenous and exogenous sources. Even a single DNA double-strand break (DSB) can trigger oocyte apoptosis, which can lead to accelerated depletion of the ovarian reserve, early loss of fertility and menopause. Therefore, repair of DNA damage is important for preserving the quality of oocytes to sustain fertility across the reproductive lifespan. This study aimed to evaluate the role of KU80 (encoded by the XRCC5 gene) - an essential component of the non-homologous end joining (NHEJ) pathway - in the repair of oocyte DNA DSBs during reproductive ageing, and following insult caused by the DNA-damaging chemotherapies cyclophosphamide and cisplatin.
METHODS
To investigate the importance of KU80 following endogenous and exogenous DNA damage, ovaries from conditional oocyte-specific knockout ( cKO) and wildtype (WT) mice that were aged or exposed to DNA damage-inducing chemotherapy were compared. Ovarian follicles and oocytes were quantified, morphologically assessed and analysed via immunohistochemistry for markers of DNA damage and apoptosis. In addition, chemotherapy exposed mice were superovulated, and the numbers and quality of mature metaphase- II (MII) oocytes were assessed.
RESULTS
The number of healthy follicles, atretic (dying) follicles, and corpora lutea were similar in Xrcc5 cKO and WT mice at PN50, PN200 and PN300. Additionally, primordial follicle number and ovulation rates were similar in young adult Xrcc5 cKO and WT mice following treatment with cyclophosphamide (75mg/kg), cisplatin (4mg/kg), or vehicle control (saline). Furthermore, KU80 was not essential for the repair of exogenously induced DNA damage in primordial follicle oocytes.
DISCUSSION
These data indicate that KU80 is not required for maintenance of the ovarian reserve, follicle development, or ovulation during maternal ageing. Similarly, this study also indicates that KU80 is not required for the repair of exogenously induced DSBs in the prophase-arrested oocytes of primordial follicles.
Topics: Animals; Female; Mice; Cisplatin; Cyclophosphamide; DNA; Oocytes; Ovarian Follicle; Prophase; Ku Autoantigen
PubMed: 37900135
DOI: 10.3389/fendo.2023.1268009 -
Developmental Biology Feb 2021The early stages of development involve complex sequences of morphological changes that are both reproducible from embryo to embryo and often robust to environmental...
The early stages of development involve complex sequences of morphological changes that are both reproducible from embryo to embryo and often robust to environmental variability. To investigate the relationship between reproducibility and robustness we examined cell cycle progression in early Drosophila embryos at different temperatures. Our experiments show that while the subdivision of cell cycle steps is conserved across a wide range of temperatures (5-35 °C), the relative duration of individual steps varies with temperature. We find that the transition into prometaphase is delayed at lower temperatures relative to other cell cycle events, arguing that it has a different mechanism of regulation. Using an in vivo biosensor, we quantified the ratio of activities of the major mitotic kinase, Cdk1 and one of the major mitotic phosphatases PP1. Comparing activation profile with cell cycle transition times at different temperatures indicates that in early fly embryos activation of Cdk1 drives entry into prometaphase but is not required for earlier cell cycle events. In fact, chromosome condensation can still occur when Cdk1 activity is inhibited pharmacologically. These results demonstrate that different kinases are rate-limiting for different steps of mitosis, arguing that robust inter-regulation may be needed for rapid and ordered mitosis.
Topics: Animals; CDC2 Protein Kinase; Cell Cycle; Cell Cycle Checkpoints; Cyclin B; Drosophila Proteins; Drosophila melanogaster; Embryo, Nonmammalian; Enzyme Activation; Metaphase; Mitosis; Prometaphase; Prophase; Protein Phosphatase 1; Temperature
PubMed: 33278404
DOI: 10.1016/j.ydbio.2020.11.010 -
Genes & Development Dec 2020Proper segregation during meiosis requires that homologs be connected by the combination of crossovers and sister chromatid cohesion. To generate crossovers, numerous... (Review)
Review
Proper segregation during meiosis requires that homologs be connected by the combination of crossovers and sister chromatid cohesion. To generate crossovers, numerous double-strand breaks (DSBs) are introduced throughout the genome by the conserved Spo11 endonuclease. DSB formation and its repair are then highly regulated to ensure that homologous chromosomes contain at least one crossover and no DSBs remain prior to meiosis I segregation. The synaptonemal complex (SC) is a meiosis-specific structure formed between homologous chromosomes during prophase that promotes DSB formation and biases repair of DSBs to homologs over sister chromatids. Synapsis occurs when a particular recombination pathway is successful in establishing stable interhomolog connections. In this issue of , Mu and colleagues (pp. 1605-1618) show that SC formation between individual chromosomes provides the feedback to down-regulate Spo11 activity, thereby revealing an additional function for the SC.
Topics: Chromatids; DNA Breaks, Double-Stranded; Homologous Recombination; Meiosis; Synaptonemal Complex
PubMed: 33262143
DOI: 10.1101/gad.345488.120 -
Genes Mar 2022To generate gametes, sexually reproducing organisms need to achieve a reduction in ploidy, via meiosis. Several mechanisms are set in place to ensure proper reductional... (Review)
Review
To generate gametes, sexually reproducing organisms need to achieve a reduction in ploidy, via meiosis. Several mechanisms are set in place to ensure proper reductional chromosome segregation at the first meiotic division (MI), including chromosome remodeling during late prophase I. Chromosome remodeling after crossover formation involves changes in chromosome condensation and restructuring, resulting in a compact bivalent, with sister kinetochores oriented to opposite poles, whose structure is crucial for localized loss of cohesion and accurate chromosome segregation. Here, we review the general processes involved in late prophase I chromosome remodeling, their regulation, and the strategies devised by different organisms to produce bivalents with configurations that promote accurate segregation.
Topics: Chromosome Segregation; Kinetochores; Meiosis; Meiotic Prophase I
PubMed: 35328099
DOI: 10.3390/genes13030546 -
ELife Jan 2023Meiotic chromosome segregation relies on synapsis and crossover (CO) recombination between homologous chromosomes. These processes require multiple steps that are...
Meiotic chromosome segregation relies on synapsis and crossover (CO) recombination between homologous chromosomes. These processes require multiple steps that are coordinated by the meiotic cell cycle and monitored by surveillance mechanisms. In diverse species, failures in chromosome synapsis can trigger a cell cycle delay and/or lead to apoptosis. How this key step in 'homolog engagement' is sensed and transduced by meiotic cells is unknown. Here we report that in , recruitment of the Polo-like kinase PLK-2 to the synaptonemal complex triggers phosphorylation and inactivation of CHK-2, an early meiotic kinase required for pairing, synapsis, and double-strand break (DSB) induction. Inactivation of CHK-2 terminates DSB formation and enables CO designation and cell cycle progression. These findings illuminate how meiotic cells ensure CO formation and accurate chromosome segregation.
Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Checkpoint Kinase 2; Chromosome Pairing; Meiosis; Synaptonemal Complex
PubMed: 36700544
DOI: 10.7554/eLife.84492 -
The Journal of Biological Chemistry Jul 2021RAD51-associated protein 1 (RAD51AP1) is a key protein in the homologous recombination (HR) DNA repair pathway. Loss of RAD51AP1 leads to defective HR, genome...
RAD51-associated protein 1 (RAD51AP1) is a key protein in the homologous recombination (HR) DNA repair pathway. Loss of RAD51AP1 leads to defective HR, genome instability, and telomere erosion. RAD51AP1 physically interacts with the RAD51 recombinase and promotes RAD51-mediated capture of donor DNA, synaptic complex assembly, and displacement-loop formation when tested with nucleosome-free DNA substrates. In cells, however, DNA is packaged into chromatin, posing an additional barrier to the complexities of the HR reaction. In this study, we show that RAD51AP1 binds to nucleosome core particles (NCPs), the minimum basic unit of chromatin in which approximately two superhelical turns of 147 bp double-stranded DNA are wrapped around one histone octamer with no free DNA ends remaining. We identified a C-terminal region in RAD51AP1, including its previously mapped DNA-binding domain, as critical for mediating the association between RAD51AP1 and both the NCP and the histone octamer. Using in vitro surrogate assays of HR activity, we show that RAD51AP1 is capable of promoting duplex DNA capture and initiating joint-molecule formation with the NCP and chromatinized template DNA, respectively. Together, our results suggest that RAD51AP1 directly assists in the RAD51-mediated search for donor DNA in chromatin. We present a model, in which RAD51AP1 anchors the DNA template through affinity for its nucleosomes to the RAD51-ssDNA nucleoprotein filament.
Topics: Chromatin; Chromosome Pairing; DNA; DNA-Binding Proteins; Genomic Instability; Histones; Humans; Nucleosomes; Protein Domains; RNA-Binding Proteins; Rad51 Recombinase; Recombinational DNA Repair; Telomere
PubMed: 34058198
DOI: 10.1016/j.jbc.2021.100844 -
Cells May 2020During oocyte development, meiosis arrests in prophase of the first division for a remarkably prolonged period firstly during oocyte growth, and then when awaiting the... (Review)
Review
During oocyte development, meiosis arrests in prophase of the first division for a remarkably prolonged period firstly during oocyte growth, and then when awaiting the appropriate hormonal signals for egg release. This prophase arrest is finally unlocked when locally produced maturation initiation hormones (MIHs) trigger entry into M-phase. Here, we assess the current knowledge of the successive cellular and molecular mechanisms responsible for keeping meiotic progression on hold. We focus on two model organisms, the amphibian , and the hydrozoan jellyfish Conserved mechanisms govern the initial meiotic programme of the oocyte prior to oocyte growth and also, much later, the onset of mitotic divisions, via activation of two key kinase systems: Cdk1-Cyclin B/Gwl (MPF) for M-phase activation and Mos-MAPkinase to orchestrate polar body formation and cytostatic (CSF) arrest. In contrast, maintenance of the prophase state of the fully-grown oocyte is assured by highly specific mechanisms, reflecting enormous variation between species in MIHs, MIH receptors and their immediate downstream signalling response. Convergence of multiple signalling pathway components to promote MPF activation in some oocytes, including , is likely a heritage of the complex evolutionary history of spawning regulation, but also helps ensure a robust and reliable mechanism for gamete production.
Topics: Animals; Anura; Cell Cycle Checkpoints; Meiosis; Oocytes; Oogenesis; Scyphozoa
PubMed: 32392797
DOI: 10.3390/cells9051150