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Advanced Science (Weinheim,... Jun 2024It has been widely reported that obesity adversely impacts reproductive performance of females. However, the effects of maternal obesity on fetal germ cells remain...
It has been widely reported that obesity adversely impacts reproductive performance of females. However, the effects of maternal obesity on fetal germ cells remain poorly understood. In the present study, by employing a high-fat diet (HFD)-based mouse model, it is discovered that maternal obesity disrupts the chromosomal synapsis and homologous recombination during fetal oogenesis. Moreover, transcriptomic profiling reveales the potential molecular network controlling this process. Of note, the global hypermethylation of genomic DNA in fetal oocytes from obese mouse is detected. Importantly, time-restricted feeding (TRF) of obese mice not only ameliorate the meiotic defects, but also partly restore the epigenetic remodeling in fetal oocytes. In sum, the evidence are provided showing the deficit fetal oogenesis in obese mother, implicating a mechanism underlying the intergenerational effects of environmental insults. TRF may represent a potentially effective approach for mitigating fertility issues in obese patients.
PubMed: 38868907
DOI: 10.1002/advs.202309184 -
The EMBO Journal Jun 2024MCM8 has emerged as a core gene in reproductive aging and is crucial for meiotic homologous recombination repair. It also safeguards genome stability by coordinating the...
MCM8 has emerged as a core gene in reproductive aging and is crucial for meiotic homologous recombination repair. It also safeguards genome stability by coordinating the replication stress response during mitosis, but its function in mitotic germ cells remains elusive. Here we found that disabling MCM8 in mice resulted in proliferation defects of primordial germ cells (PGCs) and ultimately impaired fertility. We further demonstrated that MCM8 interacted with two known helicases DDX5 and DHX9, and loss of MCM8 led to R-loop accumulation by reducing the retention of these helicases at R-loops, thus inducing genome instability. Cells expressing premature ovarian insufficiency-causative mutants of MCM8 with decreased interaction with DDX5 displayed increased R-loop levels. These results show MCM8 interacts with R-loop-resolving factors to prevent R-loop-induced DNA damage, which may contribute to the maintenance of genome integrity of PGCs and reproductive reserve establishment. Our findings thus reveal an essential role for MCM8 in PGC development and improve our understanding of reproductive aging caused by genome instability in mitotic germ cells.
PubMed: 38858601
DOI: 10.1038/s44318-024-00134-0 -
BioRxiv : the Preprint Server For... May 2024Meiotic recombination is required for faithful chromosome segregation in most sexually reproducing organisms and shapes the distribution of genetic variation in...
Meiotic recombination is required for faithful chromosome segregation in most sexually reproducing organisms and shapes the distribution of genetic variation in populations. Both the overall rate and the spatial distribution of crossovers vary within and between species. Adjacent crossovers on the same chromosome tend to be spaced more evenly than expected at random, a phenomenon known as crossover interference. Although interference has been observed in many taxa, the factors that influence the strength of interference are not well understood. We used house mice (), a well-established model system for understanding recombination, to study the effects of genetics and age on recombination rate and interference in the male germline. We analyzed crossover positions in 503 progeny from reciprocal F1 hybrids between inbred strains representing the three major subspecies of house mice. Consistent with previous studies, autosomal alleles from tend to increase recombination rate, while inheriting a X chromosome decreases recombination rate. Old males transmit an average of 0.6 more crossovers per meiosis (5.0%) than young males, though the effect varies across genetic backgrounds. We show that the strength of crossover interference depends on genotype, providing a rare demonstration that interference evolves over short timescales. Differences between reciprocal F1s suggest that X-linked factors modulate the strength of interference. Our findings motivate additional comparisons of interference among recently diverged species and further examination of the role of paternal age in determining the number and positioning of crossovers.
PubMed: 38854148
DOI: 10.1101/2024.05.28.596233 -
BioRxiv : the Preprint Server For... May 2024An model of human meiosis would accelerate research into this important reproductive process and development of therapies for infertility. We have developed a method to...
An model of human meiosis would accelerate research into this important reproductive process and development of therapies for infertility. We have developed a method to induce meiosis starting from male or female human pluripotent stem cells. We demonstrate that DNMT1 inhibition, retinoid signaling activation, and overexpression of regulatory factors (anti-apoptotic BCL2, and pro-meiotic HOXB5, BOLL, or MEIOC) rapidly activates meiosis, with leptonema beginning at 6 days, zygonema at 9 days, and pachynema at 12 days. Immunofluorescence microscopy shows key aspects of meiosis, including chromosome synapsis and sex body formation. The meiotic cells express genes similar to meiotic oogonia , including all synaptonemal complex components and machinery for meiotic recombination. These findings establish an accessible system for inducing human meiosis .
PubMed: 38854076
DOI: 10.1101/2024.05.31.596483 -
Yeast (Chichester, England) Jun 2024Meiotic crossovers play a vital role in proper chromosome segregation and evolution of most sexually reproducing organisms. Meiotic recombination can be visually...
Meiotic crossovers play a vital role in proper chromosome segregation and evolution of most sexually reproducing organisms. Meiotic recombination can be visually observed in Saccharomyces cerevisiae tetrads using linked spore-autonomous fluorescent markers placed at defined intervals within the genome, which allows for analysis of meiotic segregation without the need for tetrad dissection. To automate the analysis, we developed a deep learning-based image recognition and classification pipeline for high-throughput tetrad detection and meiotic crossover classification. As a proof of concept, we analyzed a large image data set from wild-type and selected gene knock-out mutants to quantify crossover frequency, interference, chromosome missegregation, and gene conversion events. The deep learning-based method has the potential to accelerate the discovery of new genes involved in meiotic recombination in S. cerevisiae such as the underlying factors controlling crossover frequency and interference.
PubMed: 38850080
DOI: 10.1002/yea.3965 -
G3 (Bethesda, Md.) Jun 2024Accurate chromosome segregation during meiosis requires maintenance of sister chromatid cohesion, initially established during premeiotic S phase. In human oocytes, DNA...
Accurate chromosome segregation during meiosis requires maintenance of sister chromatid cohesion, initially established during premeiotic S phase. In human oocytes, DNA replication and cohesion establishment occur decades before chromosome segregation and deterioration of meiotic cohesion is one factor that leads to increased segregation errors as women age. Our previous work led us to propose that a cohesion rejuvenation program operates to establish new cohesive linkages during meiotic prophase in Drosophila oocytes and depends on the cohesin loader Nipped-B and the cohesion establishment factor Eco. In support of this model, we recently demonstrated that chromosome-associated cohesin turns over extensively during meiotic prophase and failure to load cohesin onto chromosomes after premeiotic S phase results in arm cohesion defects in Drosophila oocytes. To identify proteins required for prophase cohesion rejuvenation but not S phase establishment, we conducted a Gal4-UAS inducible RNAi screen that utilized two distinct germline drivers. Using this strategy, we identified 29 gene products for which hairpin expression during meiotic prophase, but not premeiotic S phase, significantly increased segregation errors. Prophase knockdown of Brahma or Pumilio, two positives with functional links to the cohesin loader, caused a significant elevation in the missegregation of recombinant homologs, a phenotype consistent with premature loss of arm cohesion. Moreover, fluorescence in situ hybridization confirmed that Brahma, Pumilio and Nipped-B are required during meiotic prophase for maintenance of arm cohesion. Our data support the model that Brahma and Pumilio regulate Nipped-B dependent cohesin loading during rejuvenation. Future analyses will better define the mechanism(s) that govern meiotic cohesion rejuvenation and whether additional prophase-specific positives function in this process.
PubMed: 38849129
DOI: 10.1093/g3journal/jkae123 -
The Journal of Biological Chemistry Jun 2024Meiosis reduces ploidy through two rounds of chromosome segregation preceded by one round of DNA replication. In meiosis I, homologous chromosomes segregate, while in...
Meiosis reduces ploidy through two rounds of chromosome segregation preceded by one round of DNA replication. In meiosis I, homologous chromosomes segregate, while in meiosis II, sister chromatids separate from each other. Topoisomerase II (Topo II) is a conserved enzyme that alters DNA structure by introducing transient double-strand breaks. During mitosis, Topo II relieves topological stress associated with unwinding DNA during replication, recombination, and sister chromatid segregation. Topo II also plays a role in maintaining mitotic chromosome structure. However, the role and regulation of Topo II during meiosis is not well-defined. Previously, we found an allele of Topo II, top-2(it7), disrupts homologous chromosome segregation during meiosis I of Caenorhabditis elegans spermatogenesis. In a genetic screen, we identified different point mutations in 5'-tyrosyl-DNA phosphodiesterase two (Tdp2, C. elegans tdpt-1) that suppress top-2(it7) embryonic lethality. Tdp2 removes trapped Top-2-DNA complexes. The tdpt-1 suppressing mutations rescue embryonic lethality, ameliorate chromosome segregation defects, and restore TOP-2 protein levels of top-2(it7). Here, we show that both TOP-2 and TDPT-1 are expressed in germ line nuclei but occupy different compartments until late meiotic prophase. We also demonstrate that tdpt-1 suppression is due to loss of function of the protein and that the tdpt-1 mutations do not have a phenotype independent of top-2(it7) in meiosis. Lastly, we found that the tdpt-1 suppressing mutations either impair the phosphodiesterase activity, affect the stability of TDPT-1, or disrupt protein interactions. This suggests that the WT TDPT-1 protein is inhibiting chromosome biological functions of an impaired TOP-2 during meiosis.
PubMed: 38844130
DOI: 10.1016/j.jbc.2024.107446 -
Current Opinion in Plant Biology Jun 2024Meiosis is a conserved eukaryotic cell division that produces spores required for sexual reproduction. During meiosis, chromosomes pair and undergo programmed DNA... (Review)
Review
Meiosis is a conserved eukaryotic cell division that produces spores required for sexual reproduction. During meiosis, chromosomes pair and undergo programmed DNA double-strand breaks, followed by homologous repair that can result in reciprocal crossovers. Crossover formation is highly regulated with typically few events per homolog pair. Crossovers additionally show wider spacing than expected from uniformly random placement - defining the phenomenon of interference. In plants, the conserved HEI10 E3 ligase is initially loaded along meiotic chromosomes, before maturing into a small number of foci, corresponding to crossover locations. We review the coarsening model that explains these dynamics as a diffusion and aggregation process, resulting in approximately evenly spaced HEI10 foci. We review how underlying chromatin states, and the presence of interhomolog polymorphisms, shape the meiotic recombination landscape, in light of the coarsening model. Finally, we consider future directions to understand the control of meiotic recombination in plant genomes.
PubMed: 38838583
DOI: 10.1016/j.pbi.2024.102570 -
Molecular Biology and Evolution Jun 2024It is commonly thought that the long-term advantage of meiotic recombination is to dissipate genetic linkage, allowing natural selection to act independently on...
It is commonly thought that the long-term advantage of meiotic recombination is to dissipate genetic linkage, allowing natural selection to act independently on different loci. It is thus theoretically expected that genes with higher recombination rates evolve under more effective selection. On the other hand, recombination is often associated with GC-biased gene conversion (gBGC), which theoretically interferes with selection by promoting the fixation of deleterious GC alleles. To test these predictions, several studies assessed whether selection was more effective in highly recombining genes (due to dissipation of genetic linkage) or less effective (due to gBGC), assuming a fixed distribution of fitness effects (DFE) for all genes. In this study, I directly derive the DFE from a gene's evolutionary history (shaped by mutation, selection, drift, and gBGC) under empirical fitness landscapes. I show that genes that have experienced high levels of gBGC are less fit and thus have more opportunities for beneficial mutations. Only a small decrease in the genome-wide intensity of gBGC leads to the fixation of these beneficial mutations, particularly in highly recombining genes. This results in increased positive selection in highly recombining genes that is not caused by more effective selection. Additionally, I show that the death of a recombination hotspot can lead to a higher dN/dS than its birth, but with substitution patterns biased towards AT, and only at selected positions. This shows that controlling for a substitution bias towards GC is therefore not sufficient to rule out the contribution of gBGC to signatures of accelerated evolution. Finally, although gBGC does not affect the fixation probability of GC-conservative mutations, I show that by altering the DFE, gBGC can also significantly affect nonsynonymous GC-conservative substitution patterns.
Topics: Selection, Genetic; Recombination, Genetic; Models, Genetic; Evolution, Molecular; Gene Conversion; Genetic Fitness; Mutation; Base Composition; Genetic Linkage
PubMed: 38829800
DOI: 10.1093/molbev/msae107 -
Nucleic Acids Research Jun 2024In vertebrates, the BRCA2 protein is essential for meiotic and somatic homologous recombination due to its interaction with the RAD51 and DMC1 recombinases through FxxA...
In vertebrates, the BRCA2 protein is essential for meiotic and somatic homologous recombination due to its interaction with the RAD51 and DMC1 recombinases through FxxA and FxPP motifs (here named A- and P-motifs, respectively). The A-motifs present in the eight BRC repeats of BRCA2 compete with the A-motif of RAD51, which is responsible for its self-oligomerization. BRCs thus disrupt RAD51 nucleoprotein filaments in vitro. The role of the P-motifs is less studied. We recently found that deletion of Brca2 exons 12-14 encoding one of them (the prototypical 'PhePP' motif), disrupts DMC1 but not RAD51 function in mouse meiosis. Here we provide a mechanistic explanation for this phenotype by solving the crystal structure of the complex between a BRCA2 fragment containing the PhePP motif and DMC1. Our structure reveals that, despite sharing a conserved phenylalanine, the A- and P-motifs bind to distinct sites on the ATPase domain of the recombinases. The P-motif interacts with a site that is accessible in DMC1 octamers and nucleoprotein filaments. Moreover, we show that this interaction also involves the adjacent protomer and thus increases the stability of the DMC1 nucleoprotein filaments. We extend our analysis to other P-motifs from RAD51AP1 and FIGNL1.
PubMed: 38828772
DOI: 10.1093/nar/gkae452