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PLoS Computational Biology May 2024During meiosis, pairing of homologous chromosomes (homologs) ensures the formation of haploid gametes from diploid precursor cells, a prerequisite for sexual...
During meiosis, pairing of homologous chromosomes (homologs) ensures the formation of haploid gametes from diploid precursor cells, a prerequisite for sexual reproduction. Pairing during meiotic prophase I facilitates crossover recombination and homolog segregation during the ensuing reductional cell division. Mechanisms that ensure stable homolog alignment in the presence of an excess of non-homologous chromosomes have remained elusive, but rapid chromosome movements appear to play a role in the process. Apart from homolog attraction, provided by early intermediates of homologous recombination, dissociation of non-homologous associations also appears to contribute to homolog pairing, as suggested by the detection of stable non-homologous chromosome associations in pairing-defective mutants. Here, we have developed an agent-based model for homolog pairing derived from the dynamics of a naturally occurring chromosome ensemble. The model simulates unidirectional chromosome movements, as well as collision dynamics determined by attractive and repulsive forces arising from close-range physical interactions. Chromosome number and size as well as movement velocity and repulsive forces are identified as key factors in the kinetics and efficiency of homologous pairing in addition to homolog attraction. Dissociation of interactions between non-homologous chromosomes may contribute to pairing by crowding homologs into a limited nuclear area thus creating preconditions for close-range homolog attraction. Incorporating natural chromosome lengths, the model accurately recapitulates efficiency and kinetics of homolog pairing observed for wild-type and mutant meiosis in budding yeast, and can be adapted to nuclear dimensions and chromosome sets of other organisms.
Topics: Meiosis; Chromosome Pairing; Models, Genetic; Saccharomyces cerevisiae; Chromosomes, Fungal; Cell Nucleus; Computer Simulation; Computational Biology
PubMed: 38739641
DOI: 10.1371/journal.pcbi.1011416 -
Nature Communications Apr 2024Meiotic prophase progression is differently regulated in males and females. In males, pachytene transition during meiotic prophase is accompanied by robust alteration in...
Meiotic prophase progression is differently regulated in males and females. In males, pachytene transition during meiotic prophase is accompanied by robust alteration in gene expression. However, how gene expression is regulated differently to ensure meiotic prophase completion in males remains elusive. Herein, we identify HSF5 as a male germ cell-specific heat shock transcription factor (HSF) for meiotic prophase progression. Genetic analyzes and single-cell RNA-sequencing demonstrate that HSF5 is essential for progression beyond the pachytene stage under non-stress conditions rather than heat stress. Chromatin binding analysis in vivo and DNA-binding assays in vitro suggest that HSF5 binds to promoters in a subset of genes associated with chromatin organization. HSF5 recognizes a DNA motif different from typical heat shock elements recognized by other canonical HSFs. This study suggests that HSF5 is an atypical HSF that is required for the gene expression program for pachytene transition during meiotic prophase in males.
Topics: Mice; Male; Heat Shock Transcription Factors; Meiotic Prophase I; Mice, Knockout; Mice, Inbred C57BL; Spermatogenesis; Testis; Heat-Shock Response; Female
PubMed: 38684656
DOI: 10.1038/s41467-024-47601-0 -
Scientific Reports Apr 2024DNA double-strand breaks (DSBs) activate DNA damage responses (DDRs) in both mitotic and meiotic cells. A single-stranded DNA (ssDNA) binding protein, Replication...
DNA double-strand breaks (DSBs) activate DNA damage responses (DDRs) in both mitotic and meiotic cells. A single-stranded DNA (ssDNA) binding protein, Replication protein-A (RPA) binds to the ssDNA formed at DSBs to activate ATR/Mec1 kinase for the response. Meiotic DSBs induce homologous recombination monitored by a meiotic DDR called the recombination checkpoint that blocks the pachytene exit in meiotic prophase I. In this study, we further characterized the essential role of RPA in the maintenance of the recombination checkpoint during Saccharomyces cerevisiae meiosis. The depletion of an RPA subunit, Rfa1, in a recombination-defective dmc1 mutant, fully alleviates the pachytene arrest with the persistent unrepaired DSBs. RPA depletion decreases the activity of a meiosis-specific CHK2 homolog, Mek1 kinase, which in turn activates the Ndt80 transcriptional regulator for pachytene exit. These support the idea that RPA is a sensor of ssDNAs for the activation of meiotic DDR. Rfa1 depletion also accelerates the prophase I delay in the zip1 mutant defective in both chromosome synapsis and the recombination, consistent with the notion that the accumulation of ssDNAs rather than defective synapsis triggers prophase I delay in the zip1 mutant.
Topics: Replication Protein A; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Meiosis; DNA Breaks, Double-Stranded; Cell Cycle Proteins; DNA-Binding Proteins; Recombination, Genetic; Homologous Recombination; MAP Kinase Kinase 1; DNA, Single-Stranded; Nuclear Proteins; Transcription Factors
PubMed: 38664461
DOI: 10.1038/s41598-024-60082-x -
Plant Physiology Mar 2024During meiotic prophase I, chromosomes undergo large-scale dynamics to allow homologous chromosome pairing, prior to which chromosome ends attach to the inner nuclear...
During meiotic prophase I, chromosomes undergo large-scale dynamics to allow homologous chromosome pairing, prior to which chromosome ends attach to the inner nuclear envelope and form a chromosomal bouquet. Chromosome pairing is crucial for homologous recombination and accurate chromosome segregation during meiosis. However, the specific mechanism by which homologous chromosomes recognize each other is poorly understood. Here, we investigated the process of homologous chromosome pairing during early prophase I of meiosis in rice (Oryza sativa) using pooled oligo probes specific to an entire chromosome or chromosome arm. We revealed that chromosome pairing begins from both ends and extends towards the center from early zygotene through late zygotene. Genetic analysis of both trisomy and autotetraploidy also showed that pairing initiation is induced by both ends of a chromosome. However, healed ends that lack the original terminal regions on telocentric and acrocentric chromosomes cannot initiate homologous chromosome pairing, even though they may still enter the telomere clustering region at the bouquet stage. Furthermore, a chromosome that lacks the distal parts on both sides loses the ability to pair with other intact chromosomes. Thus, the native ends of chromosomes play a crucial role in initiating homologous chromosome pairing during meiosis and likely have a substantial impact on genome differentiation.
PubMed: 38478471
DOI: 10.1093/plphys/kiae152 -
Nucleic Acids Research May 2024Accurate chromosome segregation during meiosis requires the establishment of at least one crossover (CO) between each pair of homologous chromosomes. CO formation...
Accurate chromosome segregation during meiosis requires the establishment of at least one crossover (CO) between each pair of homologous chromosomes. CO formation depends on a group of conserved pro-CO proteins, which colocalize at CO-designated sites during late meiotic prophase I. However, it remains unclear whether these pro-CO proteins form a functional complex and how they promote meiotic CO formation in vivo. Here, we show that COSA-1, a key component required for CO formation, interacts with other pro-CO factors, MSH-5 and ZHP-3, via its N-terminal disordered region. Point mutations that impair these interactions do not affect CO designation, but they strongly hinder the accumulation of COSA-1 at CO-designated sites and result in defective CO formation. These defects can be partially bypassed by artificially tethering an interaction-compromised COSA-1 derivate to ZHP-3. Furthermore, we revealed that the accumulation of COSA-1 into distinct foci is required to assemble functional 'recombination nodules'. These prevent early CO-designated recombination intermediates from being dismantled by the RTEL-1 helicase and protect late recombination intermediates, such as Holliday junctions, until they are resolved by CO-specific resolvases. Altogether, our findings provide insight into COSA-1 mediated pro-CO complex assembly and its contribution to CO formation.
Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Chromosome Segregation; Crossing Over, Genetic; DNA-Binding Proteins; Meiosis
PubMed: 38412290
DOI: 10.1093/nar/gkae130 -
Reproduction (Cambridge, England) Apr 2024The dissociation of HORMA domain protein 2 (HORMAD2) from the synaptonemal complex is tightly regulated. This study reveals that the N-terminal region of HORMAD2 is...
IN BRIEF
The dissociation of HORMA domain protein 2 (HORMAD2) from the synaptonemal complex is tightly regulated. This study reveals that the N-terminal region of HORMAD2 is critical for its dissociation from synapsed meiotic chromosomes.
ABSTRACT
During meiosis, homologous chromosomes undergo synapsis and recombination. HORMA domain proteins regulate key processes in meiosis. Mammalian HORMAD1 and HORMAD2 localize to unsynapsed chromosome axes but are removed upon synapsis by the TRIP13 AAA+ ATPase. TRIP13 engages the N-terminal region of HORMA domain proteins to induce an open conformation, resulting in the disassembly of protein complexes. Here, we report introduction of a 3×FLAG-HA tag to the N-terminus of HORMAD2 in mice. Coimmunoprecipitation coupled with mass spectrometry identified HORMAD1 and SYCP2 as HORMAD2-associated proteins in the testis. Unexpectedly, the N-terminal tagging of HORMAD2 resulted in its abnormal persistence along synapsed regions in pachynema and ectopic localization to telomeres in diplonema. Super-resolution microscopy revealed that 3×FLAG-HA-HORMAD2 was distributed along the central region of the synaptonemal complex, whereas wild-type HORMAD1 persisted along the lateral elements in 3×FLAG-HA-HORMAD2 meiocytes. Although homozygous mice completed meiosis and were fertile, homozygous males exhibited a significant reduction in sperm count. Collectively, these results suggest that the N-terminus of HORMAD2 is important for its timely removal from meiotic chromosome axes.
Topics: Animals; Male; Mice; Cell Cycle Proteins; Chromosome Pairing; Mammals; Meiosis; Meiotic Prophase I; Semen; Synaptonemal Complex
PubMed: 38401263
DOI: 10.1530/REP-23-0330 -
Molecular Genetics & Genomic Medicine Feb 2024Recurrent miscarriage (RM) affects 1% to 5% of couples trying to conceive. Despite extensive clinical and laboratory testing, half of the RM cases remain unexplained. We...
BACKGROUND
Recurrent miscarriage (RM) affects 1% to 5% of couples trying to conceive. Despite extensive clinical and laboratory testing, half of the RM cases remain unexplained. We report the genetic analysis of a couple with eight miscarriages and the search for their potential genetic etiology.
METHODS
Short tandem repeat (STR) markers, single nucleotide polymorphic (SNP) microarray, and human DNA methylation microarray were used to analyze the genotypes of two miscarriages. Exomes sequencing was performed on DNA from the two partners and identified variants were validated by Sanger sequencing.
RESULTS
STR marker genotyping demonstrated that the two available miscarriages are triploid digynic and resulted from the failure of Meiosis II. SNP microarray analysis revealed an additional Meiosis I abnormality that is the segregation of the two maternal homologous chromosomes in one triploid miscarriage. Whole-exome sequencing on DNA from the two partners identified candidate variants only in the female partner in two genes with roles in female reproduction, a missense in EIF4ENIF1 (OMIM 607445) and a stop gain in HORMAD2 (OMIM 618842). EIF4ENIF1 is a eukaryotic translation initiation factor 4E nuclear import factor required for the oocyte germinal vesicle breakdown, and HORMAD2 is part of the synaptonemal complex that was hypothesized to act as a checkpoint mechanism to eliminate oocytes with asynapsis during meiotic prophase I in mice.
CONCLUSION
While both genes may contribute to the phenotype, the Meiosis I abnormalities in the conceptions favor the causal role of HORMAD2 in the etiology of RM in this couple. This report illustrates the importance of comprehensively analyzing the products of conception to guide the search for the genetic causation of RM.
Topics: Female; Humans; Pregnancy; Abortion, Habitual; Codon, Terminator; DNA; Meiosis; Triploidy; Male
PubMed: 38400599
DOI: 10.1002/mgg3.2402 -
ELife Feb 2024Meiotic sex chromosome inactivation (MSCI) is a critical feature of meiotic prophase I progression in males. While the ATR kinase and its activator TOPBP1 are key...
Meiotic sex chromosome inactivation (MSCI) is a critical feature of meiotic prophase I progression in males. While the ATR kinase and its activator TOPBP1 are key drivers of MSCI within the specialized sex body (SB) domain of the nucleus, how they promote silencing remains unclear given their multifaceted meiotic functions that also include DNA repair, chromosome synapsis, and SB formation. Here we report a novel mutant mouse harboring mutations in the TOPBP1-BRCT5 domain. males are infertile, with impaired MSCI despite displaying grossly normal events of early prophase I, including synapsis and SB formation. Specific ATR-dependent events are disrupted, including phosphorylation and localization of the RNA:DNA helicase Senataxin. spermatocytes initiate, but cannot maintain ongoing, MSCI. These findings reveal a non-canonical role for the ATR-TOPBP1 signaling axis in MSCI dynamics at advanced stages in pachynema and establish the first mouse mutant that separates ATR signaling and MSCI from SB formation.
Topics: Animals; Humans; Male; Mice; Alleles; Carrier Proteins; DNA Repair; DNA-Binding Proteins; Infertility, Male; Meiosis; Nuclear Proteins; Sex Chromosomes
PubMed: 38391183
DOI: 10.7554/eLife.90887 -
Genes & Development Mar 2024H3K9 trimethylation (H3K9me3) plays emerging roles in gene regulation, beyond its accumulation on pericentric constitutive heterochromatin. It remains a mystery why and...
H3K9 trimethylation (H3K9me3) plays emerging roles in gene regulation, beyond its accumulation on pericentric constitutive heterochromatin. It remains a mystery why and how H3K9me3 undergoes dynamic regulation in male meiosis. Here, we identify a novel, critical regulator of H3K9 methylation and spermatogenic heterochromatin organization: the germline-specific protein ATF7IP2 (MCAF2). We show that in male meiosis, ATF7IP2 amasses on autosomal and X-pericentric heterochromatin, spreads through the entirety of the sex chromosomes, and accumulates on thousands of autosomal promoters and retrotransposon loci. On the sex chromosomes, which undergo meiotic sex chromosome inactivation (MSCI), the DNA damage response pathway recruits ATF7IP2 to X-pericentric heterochromatin, where it facilitates the recruitment of SETDB1, a histone methyltransferase that catalyzes H3K9me3. In the absence of ATF7IP2, male germ cells are arrested in meiotic prophase I. Analyses of ATF7IP2-deficient meiosis reveal the protein's essential roles in the maintenance of MSCI, suppression of retrotransposons, and global up-regulation of autosomal genes. We propose that ATF7IP2 is a downstream effector of the DDR pathway in meiosis that coordinates the organization of heterochromatin and gene regulation through the spatial regulation of SETDB1-mediated H3K9me3 deposition.
Topics: Germ Cells; Heterochromatin; Histones; Meiosis; Methylation; Male
PubMed: 38383062
DOI: 10.1101/gad.351569.124 -
PLoS Genetics Feb 2024Meiotic recombination between homologous chromosomes is initiated by the formation of hundreds of programmed double-strand breaks (DSBs). Approximately 10% of these DSBs...
Meiotic recombination between homologous chromosomes is initiated by the formation of hundreds of programmed double-strand breaks (DSBs). Approximately 10% of these DSBs result in crossovers (COs), sites of physical DNA exchange between homologs that are critical to correct chromosome segregation. Virtually all COs are formed by coordinated efforts of the MSH4/MSH5 and MLH1/MLH3 heterodimers, the latter representing the defining marks of CO sites. The regulation of CO number and position is poorly understood, but undoubtedly requires the coordinated action of multiple repair pathways. In a previous report, we found gene-trap disruption of the DNA helicase, FANCJ (BRIP1/BACH1), elicited elevated numbers of MLH1 foci and chiasmata. In somatic cells, FANCJ interacts with numerous DNA repair proteins including MLH1, and we hypothesized that FANCJ functions with MLH1 to regulate the major CO pathway. To further elucidate the meiotic function of FANCJ, we produced three new Fancj mutant mouse lines via CRISPR/Cas9 gene editing: a full-gene deletion, truncation of the N-terminal Helicase domain, and a C-terminal dual-tagged allele. We also generated an antibody against the C-terminus of the mouse FANCJ protein. Surprisingly, none of our Fancj mutants show any change in either MLH1 focus counts during pachynema or total CO number at diakinesis of prophase I. We find evidence that FANCJ and MLH1 do not interact in meiosis; further, FANCJ does not co-localize with MSH4, MLH1, or MLH3 in meiosis. Instead, FANCJ co-localizes with BRCA1 and TOPBP1, forming discrete foci along the chromosome cores beginning in early meiotic prophase I and densely localized to unsynapsed chromosome axes in late zygonema and to the XY chromosomes in early pachynema. Fancj mutants also exhibit a subtle persistence of DSBs in pachynema. Collectively, these data indicate a role for FANCJ in early DSB repair, but they rule out a role for FANCJ in MLH1-mediated CO events.
Topics: Animals; Male; Mice; Alleles; DNA Helicases; DNA Repair; Meiosis; Meiotic Prophase I
PubMed: 38377115
DOI: 10.1371/journal.pgen.1011175