The biggest effect appeared in women who had lost the function of a gene called CHEK2, which caused an average 3.5-year delay in menopause.Ruth, K. S. et al. Nature https://doi.org/10.1038/s41586-021-03779-7 (2021).//Genetic insights into biological mechanisms governing human ovarian ageing. Ruth KS et al. (2021) Reproductive longevity is essential for fertility and influences healthy ageing in women1,2, but insights into its underlying biological mechanisms and treatments to preserve it are limited. Here we identify 290 genetic determinants of ovarian ageing, assessed using normal variation in age at natural menopause (ANM) in about 200,000 women of European ancestry. These common alleles were associated with clinical extremes of ANM; women in the top 1% of genetic susceptibility have an equivalent risk of premature ovarian insufficiency to those carrying monogenic FMR1 premutations3. The identified loci implicate a broad range of DNA damage response (DDR) processes and include loss-of-function variants in key DDR-associated genes. Integration with experimental models demonstrates that these DDR processes act across the life-course to shape the ovarian reserve and its rate of depletion. Furthermore, we demonstrate that experimental manipulation of DDR pathways highlighted by human genetics increases fertility and extends reproductive life in mice. Causal inference analyses using the identified genetic variants indicate that extending reproductive life in women improves bone health and reduces risk of type 2 diabetes, but increases the risk of hormone-sensitive cancers. These findings provide insight into the mechanisms that govern ovarian ageing, when they act, and how they might be targeted by therapeutic approaches to extend fertility and prevent disease./////////////////////// Inactivating Chek2 in mice reduced ovarian degeneration and, in animals that were around the age of the mouse equivalent of menopause, increased the ovarian response to hormonal stimulation, consistent with these animals having a greater ovarian reserve than that of control mice (Fig. 1b). Fertilization rates in mice lacking Chek2 were unaffected, as were embryonic development and litter size.
NCBI Summary:
In response to DNA damage and replication blocks, cell cycle progression is halted through the control of critical cell cycle regulators. The protein encoded by this gene is a cell cycle checkpoint regulator and putative tumor suppressor. It contains a forkhead-associated protein interaction domain essential for activation in response to DNA damage and is rapidly phosphorylated in response to replication blocks and DNA damage. When activated, the encoded protein is known to inhibit CDC25C phosphatase, preventing entry into mitosis, and has been shown to stabilize the tumor suppressor protein p53, leading to cell cycle arrest in G1. In addition, this protein interacts with and phosphorylates BRCA1, allowing BRCA1 to restore survival after DNA damage. Mutations in this gene have been linked with Li-Fraumeni syndrome, a highly penetrant familial cancer phenotype usually associated with inherited mutations in TP53. Also, mutations in this gene are thought to confer a predisposition to sarcomas, breast cancer, and brain tumors. This nuclear protein is a member of the CDS1 subfamily of serine/threonine protein kinases. Several transcript variants encoding different isoforms have been found for this gene. [provided by RefSeq, Apr 2012]
General function
Cell cycle regulation, DNA repair
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Cellular localization
Nuclear
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Ovarian function
Oogenesis, Oocyte maturation, Early embryo development
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The DNA Damage Checkpoint Eliminates Mouse Oocytes with Chromosome Synapsis Failure. Rinaldi VD et al. (2017) Pairing and synapsis of homologous chromosomes during meiosis is crucial for producing genetically normal gametes and is dependent upon repair of SPO11-induced double-strand breaks (DSBs) by homologous recombination. To prevent transmission of genetic defects, diverse organisms have evolved mechanisms to eliminate meiocytes containing unrepaired DSBs or unsynapsed chromosomes. Here we show that the CHK2 (CHEK2)-dependent DNA damage checkpoint culls not only recombination-defective mouse oocytes but also SPO11-deficient oocytes that are severely defective in homolog synapsis. The checkpoint is triggered in oocytes that accumulate a threshold level of spontaneous DSBs (∼10) in late prophase I, the repair of which is inhibited by the presence of HORMAD1/2 on unsynapsed chromosome axes. Furthermore, Hormad2 deletion rescued the fertility of oocytes containing a synapsis-proficient, DSB repair-defective mutation in a gene (Trip13) required for removal of HORMADs from synapsed chromosomes, suggesting that many meiotic DSBs are normally repaired by intersister recombination in mice.//////////////////
Inhibitory phosphorylation of Cdk1 mediates prolonged prophase I arrest in female germ cells and is essential for female reproductive lifespan. Adhikari D et al. (2016) A unique feature of female germ cell development in mammals is their remarkably long arrest at the prophase of meiosis I, which lasts up to 50 years in humans. Both dormant and growing oocytes are arrested at prophase I and completely lack the ability to resume meiosis. Here, we show that the prolonged meiotic arrest of female germ cells is largely achieved via the inhibitory phosphorylation of Cdk1 (cyclin-dependent kinase 1). In two mouse models where we have introduced mutant Cdk1(T14AY15F) which cannot be inhibited by phosphorylation (Cdk1AF) in small meiotically incompetent oocytes, the prophase I arrest is interrupted, leading to a premature loss of female germ cells. We show that in growing oocytes, Cdk1AF leads to premature resumption of meiosis with condensed chromosomes and germinal vesicle breakdown followed by oocyte death, whereas in dormant oocytes, Cdk1AF leads to oocyte death directly, and both situations damage the ovarian reserve that maintains the female reproductive lifespan, which should be around 1 year in mice. Furthermore, interruption of the inhibitory phosphorylation of Cdk1 results in DNA damage, which is accompanied by induction of the Chk2 (checkpoint kinase 2)-p53/p63-dependent cell death pathway, which eventually causes global oocyte death. Together, our data demonstrate that the phosphorylation-mediated suppression of Cdk1 activity is one of the crucial factors that maintain the lengthy prophase arrest in mammalian female germ cells, which is essential for preserving the germ cell pool and reproductive lifespan in female mammals.//////////////////
Chk2 Regulates Cell Cycle Progression during Mouse Oocyte Maturation and Early Embryo Development. Dai XX 2014 et al.
As a tumor suppressor homologue during mitosis, Chk2 is involved in replication checkpoints, DNA repair, and cell cycle arrest, although its functions during mouse oocyte meiosis and early embryo development remain uncertain. We investigated the functions of Chk2 during mouse oocyte maturation and early embryo development. Chk2 exhibited a dynamic localization pattern; Chk2 expression was restricted to germinal vesicles at the germinal vesicle (GV) stage, was associated with centromeres at pro-metaphase I (Pro-MI), and localized to spindle poles at metaphase I (MI). Disrupting Chk2 activity resulted in cell cycle progression defects. First, inhibitor-treated oocytes were arrested at the GV stage and failed to undergo germinal vesicle breakdown (GVBD); this could be rescued after Chk2 inhibition release. Second, Chk2 inhibition after oocyte GVBD caused MI arrest. Third, the first cleavage of early embryo development was disrupted by Chk2 inhibition. Additionally, in inhibitor-treated oocytes, checkpoint protein Bub3 expression was consistently localized at centromeres at the MI stage, which indicated that the spindle assembly checkpoint (SAC) was activated. Moreover, disrupting Chk2 activity in oocytes caused severe chromosome misalignments and spindle disruption. In inhibitor-treated oocytes, centrosome protein ?-tubulin and Polo-like kinase 1 (Plk1) were dissociated from spindle poles. These results indicated that Chk2 regulated cell cycle progression and spindle assembly during mouse oocyte maturation and early embryo development.
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Slow freezing and vitrification differentially modify the gene expression profile of human metaphase II oocytes. Monzo C et al. BACKGROUNDCryopreservation is now considered as an efficient way to store human oocytes to preserve fertility. However, little is known about the effects of this technology on oocyte gene expression. The aim of this study was to examine the effect of the two cryopreservation procedures, slow freezing and vitrification, on the gene expression profile of human metaphase II (MII) oocytes.METHODSUnfertilized MII oocytes following ICSI failure were cryopreserved either by slow freezing or by the Cryotip method for vitrification. After thawing, total RNA was extracted and analyzed using Affymetrix Human Genome U133 Plus 2.0 GeneChip arrays. The gene expression profiles and associated biological pathways in slowly frozen/thawed and vitrified MII oocytes were determined and compared with those of non-cryopreserved MII oocytes used as controls.RESULTSBoth cryopreservation procedures negatively affected the gene expression profile of human MII oocytes in comparison with controls. However, slowly frozen and vitrified MI oocytes displayed specific gene expression signatures. Slow freezing was associated with down-regulation of genes involved in chromosomal structure maintenance (KIF2C and KIF3A) and cell cycle regulation (CHEK2 and CDKN1B) that may lead to a reduction in the oocyte developmental competence. In vitrified oocytes, many genes of the ubiquitination pathway were down-regulated, including members of the ubiquitin-specific peptidase family and subunits of the 26S proteasome. Such inhibition of the degradation machinery might stabilize the maternal protein content that is necessary for oocyte developmental competence.CONCLUSIONSThe low pregnancy rates commonly observed when using human MII oocytes after slow freezing-thawing may be explained by the alterations of the oocyte gene expression profile.
Expression regulated by
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Ovarian localization
Oocyte
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Maelstrom coordinates microtubule organization during Drosophila oogenesis through interaction with components of the MTOC. Sato K et al. The establishment of body axes in multicellular organisms requires accurate control of microtubule polarization. Mutations in Drosophila PIWI-interacting RNA (piRNA) pathway genes often disrupt the axes of the oocyte. This results from the activation of the DNA damage checkpoint factor Checkpoint kinase 2 (Chk2) due to transposon derepression. A piRNA pathway gene, maelstrom (mael), is critical for the establishment of oocyte polarity in the developing egg chamber during Drosophila oogenesis. We show that Mael forms complexes with microtubule-organizing center (MTOC) components, including Centrosomin, Mini spindles, and ?Tubulin. We also show that Mael colocalizes with aTubulin and ?Tubulin to centrosomes in dividing cyst cells and follicle cells. MTOC components mislocalize in mael mutant germarium and egg chambers, leading to centrosome migration defects. During oogenesis, the loss of mael affects oocyte determination and induces egg chamber fusion. Finally, we show that the axis specification defects in mael mutants are not suppressed by a mutation in mnk, which encodes a Chk2 homolog. These findings suggest a model in which Mael serves as a platform that nucleates other MTOC components to form a functional MTOC in early oocyte development, which is independent of Chk2 activation and DNA damage signaling.
Follicle stages
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Phenotypes
Mutations
2 mutations
Species: mouse
Mutation name: None
type: null mutation fertility: fertile Comment: Reversal of female infertility by Chk2 ablation reveals the oocyte DNA damage checkpoint pathway. Bolcun-Filas E 2014 et al.
Genetic errors in meiosis can lead to birth defects and spontaneous abortions. Checkpoint mechanisms of hitherto unknown nature eliminate oocytes with unrepaired DNA damage, causing recombination-defective mutant mice to be sterile. Here, we report that checkpoint kinase 2 (Chk2 or Chek2), is essential for culling mouse oocytes bearing unrepaired meiotic or induced DNA double-strand breaks (DSBs). Female infertility caused by a meiotic recombination mutation or irradiation was reversed by mutation of Chk2. Both meiotically programmed and induced DSBs trigger CHK2-dependent activation of TRP53 (p53) and TRP63 (p63), effecting oocyte elimination. These data establish CHK2 as essential for DNA damage surveillance in female meiosis and indicate that the oocyte DSB damage response primarily involves a pathway hierarchy in which ataxia telangiectasia and Rad3-related (ATR) signals to CHK2, which then activates p53 and p63.
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Species: mouse
Mutation name: type: null mutation fertility: fertile Comment: Maximizing the ovarian reserve in mice by evading LINE-1 genotoxicity. Tharp ME et al. (2020) Female reproductive success critically depends on the size and quality of a finite ovarian reserve. Paradoxically, mammals eliminate up to 80% of the initial oocyte pool through the enigmatic process of fetal oocyte attrition (FOA). Here, we interrogate the striking correlation of FOA with retrotransposon LINE-1 (L1) expression in mice to understand how L1 activity influences FOA and its biological relevance. We report that L1 activity triggers FOA through DNA damage-driven apoptosis and the complement system of immunity. We demonstrate this by combined inhibition of L1 reverse transcriptase activity and the Chk2-dependent DNA damage checkpoint to prevent FOA. Remarkably, reverse transcriptase inhibitor AZT-treated Chk2 mutant oocytes that evade FOA initially accumulate, but subsequently resolve, L1-instigated genotoxic threats independent of piRNAs and differentiate, resulting in an increased functional ovarian reserve. We conclude that FOA serves as quality control for oocyte genome integrity, and is not obligatory for oogenesis nor fertility.//////////////////