Antagonistic roles of ubiquitin ligase HEI10 and SUMO ligase RNF212 regulate meiotic recombination

Impact of aging on spermatogenic function and reproductive outcomes in repro57 heterozygous male mice: A model for age-related infertility

PURPOSE

This study aims to investigate the histological changes, sperm parameters, and their impact on embryo development rates and offspring numbers in advanced-age male repro57 heterozygous mice, corresponding to approximately 40 years of age in humans.

METHODS

Sperm parameters were assessed in both young and advanced-age repro57 heterozygous mice, as well as in young and advanced-age wild-type mice. Additionally, testis weight and histological analysis of seminiferous tubules were conducted to identify degenerative changes. Male mice from each group were mated with young wild-type females to compare offspring numbers, and in vitro fertilization (IVF) was used to evaluate fertilization and blastocyst formation rates.

RESULTS

No significant differences in sperm concentration and motility were observed between young and aged wild-type mice or between young wild-type and young repro57 heterozygous mice. However, advanced-age repro57 heterozygous mice exhibited significantly lower sperm parameters and testis weight compared to advanced-age wild-type mice. Histological analysis revealed increased Sertoli cell vacuolation in the seminiferous tubules of advanced-age repro57 heterozygous mice. Additionally, these advanced-age mice exhibited significantly lower blastocyst formation rates and produced fewer offspring compared to advanced-age wild-type mice.

CONCLUSION

Advanced reproductive aging in repro57 heterozygous male mice is associated with marked senescence-like degenerative changes, leading to a decline in offspring numbers, attributed to increased Sertoli cell vacuolation and diminished sperm quality.

Exploring the therapeutic effect of melatonin targeting common biomarkers in testicular germ cell tumor, prostate adenocarcinoma, and male infertility: an integrated biology approach

Globally, male infertility (MI) is a major concern. Several other comorbidities related to MI are testicular germ cell tumor (TGCT) and prostate adenocarcinoma (PRAD). This study focuses on finding the common biomarkers among these diseases and their interaction with Melatonin (MLT). The differential expressed genes were retrieved using the GEPIA2 database for TGCT and PRAD, whereas the DISGENET database for MI-related genes. InteractiVenn was performed in response to identify the common genes. The STAG3, RNF212, DDX3Y, DPY19L2, TPCN1, KLK3, GNRH1, DMD, CCDC146, and DNAH1 are found to be involved in all these diseases. The gene ontologies and pathway enrichment analysis were done for these significant genes in response to identifying and accessing the involvement of these genes in other processes. MLT is a neuroendocrine hormone with high therapeutic properties. MLT showed the best binding energy with DDX3Y among all the proteins. Molecular dynamic simulation (MDS) of MLT with DDX3Y was performed and found to be -52.382 ± 13.110 kJ/mol binding energy. The RMSD, RMSF, SASA, RG, H-bond, FEL, PCA, and MM-PBSA analysis confirm the stability and compactness of the DDX3Y-MLT complex. The MDS results indicate that MLT is a promising therapeutic option for enhancing DDX3Y expression, which will support spermatogenesis. Additionally, the hub genes were identified based on MCC parameters from the merged interactive network of common genes in response to finding significant genes that can be a potential biomarker for the diagnosis of diseases.

MutLγ enforces meiotic crossovers in Arabidopsis thaliana

During meiosis, each chromosome pair experiences at least one crossover (CO), which directs their balanced segregation in addition to shuffling genetic information. COs tend to be away from each other, a phenomenon known as CO interference. The main biochemical pathway for CO formation, which is conserved in distant eukaryotes, involves the ZMM proteins together with the MLH1-MLH3 complex (MutLγ). Here, we aim to clarify the role of MutLγ in CO formation in Arabidopsis thaliana. We show that AtMutLγ is partially dispensable for ZMM-dependent CO formation. HEI10 large foci-that mark CO sites in wild-type-form at a normal level in mlh1 and mlh3 mutants, but are inefficiently maturated into COs. Mutating the MUS81 nuclease in either mlh1 or mlh3 leads to chromosome fragmentation, which is suppressed by further mutating the zmm msh5. This suggests that in the absence of MutLγ, recombination intermediates produced by ZMMs are resolved by MUS81, which does not ensure CO formation. Finally, CO interference is marginally affected in mlh1, which is compatible with a random sub-sampling of normally patterned CO sites. We conclude that AtMutLγ imposes designated recombination intermediates to be resolved exclusively as COs, supporting the view that MutLγ asymmetrically resolves double-Holliday junctions, yielding COs.

Testis-Specific PDHA2 Is Required for Proper Meiotic Recombination and Chromosome Organisation During Spermatogenesis

Proper segregation of homologous chromosomes during meiosis requires crossovers that are tightly regulated by the chromosome structure. PDHA2 is the testis-specific paralog of PDHA1, a core subunit of pyruvate dehydrogenase. However, its role during spermatogenesis is unclear. We show that PDHA2 knockout results in male infertility in mice, but meiotic DSBs in spermatocytes occur normally and are efficiently repaired. Detailed analysis reveals that mid/late recombination intermediates are moderately reduced, resulting in fewer crossovers and many chromosomes without a crossover. Furthermore, defective chromosome structure is observed, including aberrant histone modifications, defective chromosome ends, precocious release of REC8 from chromosomes and fragmented chromosome axes after pachytene. These defects contribute to the failure of pyruvate conversion to acetyl-CoA, resulting in decreased acetyl-CoA and precursors for metabolites and energy in the absence of PDHA2. These findings reveal the important functions of PDHA2 in ensuring proper crossover formation and in modulating chromosome structure during spermatogenesis.

NAE1-mediated neddylation coordinates ubiquitination regulation of meiotic recombination during spermatogenesis

Rationale: Meiotic homologous recombination is a critical event in gametogenesis, which is tightly regulated to ensure the generation of crossovers on homologous chromosomes. This process is crucial for ensuring the accurate segregation of genetic material and maintaining genetic diversity within species, ultimately contributing to reproductive success. Nevertheless, comprehensive mechanisms of post-translational modification (PTM) regulating homologous recombination during meiosis require further investigation. The aim of this study is to investigate the regulatory mechanisms and physiological functions of NAE1-mediated neddylation during meiosis of mammalian spermatogenesis and its consequential role in infertility. Methods: The dynamic localization of NAE1 at various sub-stages during spermatogenesis was determined using immunofluorescence staining and seminiferous tubule staging. We explore the role of NAE1-mediated neddylation by utilizing germ cell-specific Nae1-knockout mice. The impact on homologous synapsis and recombination during the meiosis prophase I were verified through chromosome spread fluorescence staining. We used 10 × Genomics single cell transcriptomics and ubiquitinomics to analysis the causes of spermatogenesis arrest and spermatogenic apoptosis. Results: NAE1 exhibited high nuclear expression within spermatocytes from the pachytene stage onwards. Nae1-SKO male mice showed a late-pachytene arrest in spermatocytes, resulting in infertility. In NAE1-deficient spermatocytes, there is an increase in apoptosis. Nae1 deletion led to double-strand break (DSB) repair failure with normal autosomes synapsis. From a mechanistic perspective, we verified excessive recombination intermediate stabilization and failed crossover formation, which ultimately resulted in impaired meiotic recombination. Further analysis showed that ubiquitination regulation coordinated with NAE1-mediated neddylation was implicated in meiotic recombination. Conclusion: NAE1-mediated neddylation regulates ubiquitination during meiosis and is involved in the stabilization of recombination proteins related to crossover differentiation. We provide cytological evidence for the neddylation-ubiquitination system (NUS) in mammalian meiotic recombination during spermatogenesis.

Dynamic molecular architecture of the synaptonemal complex

During meiosis, pairing between homologous chromosomes is stabilized by the assembly of the synaptonemal complex (SC). The SC ensures the formation of crossovers between homologous chromosomes and regulates their distribution. However, how the SC regulates crossover formation remains elusive. We isolated an unusual mutation in Caenorhabditis elegans that disrupts crossover interference but not SC assembly. This mutation alters the unique C terminal domain of an essential SC protein, SYP-4, a likely ortholog of the vertebrate SC protein SIX6OS1. We use three-dimensional stochastic optical reconstruction microscopy (3D-STORM) to interrogate the molecular architecture of the SC from wild-type and mutant C. elegans animals. Using a probabilistic mapping approach to analyze super-resolution image data, we detect changes in the organization of the synaptonemal complex in wild-type animals that coincide with crossover designation. We also found that our syp-4 mutant perturbs SC architecture. Our findings add to growing evidence that the SC is an active material whose molecular organization contributes to chromosome-wide crossover regulation.

Distinct and interdependent functions of three RING proteins regulate recombination during mammalian meiosis

During meiosis, each pair of homologous chromosomes becomes connected by at least one crossover, as required for accurate segregation, and adjacent crossovers are widely separated thereby limiting total numbers. In coarsening models, this crossover patterning results from nascent recombination sites competing to accrue a limiting pro-crossover RING-domain protein (COR) that diffuses between synapsed chromosomes. Here, we delineate the localization dynamics of three mammalian CORs in the mouse and determine their interdependencies. RNF212, HEI10, and the newest member RNF212B show divergent spatiotemporal dynamics along synapsed chromosomes, including profound differences in spermatocytes and oocytes, that are not easily reconciled by elementary coarsening models. Contrasting mutant phenotypes and genetic requirements indicate that RNF212B, RNF212, and HEI10 play distinct but interdependent functions in regulating meiotic recombination and coordinating the events of meiotic prophase-I by integrating signals from DNA breaks, homolog synapsis, the cell-cycle, and incipient crossover sites.

Cis-Regulatory Evolution of CCNB1IP1 Driving Gradual Increase of Cortical Size and Folding in primates

Neocortex expansion has a concerted relationship with folding, underlying evolution of human cognitive functions. However, molecular mechanisms underlying this significant evolutionary process remains unknown. Here, using tree shrew as an outgroup of primates, we identify a new regulator CCNB1IP1, which acquired its expression before the emergence of primates. Following the evolution of cis-regulatory elements, the CCNB1IP1 expression has steadily increased over the course of primate brain evolution, mirroring the gradual increase of neocortex. Mechanistically, we elucidated that CCNB1IP1 expression can cause an increase in neural progenitors through shortening G1 phase. Consistently, the CCNB1IP1 knock-in mouse model exhibited traits associated with enhanced learning and memory abilities. Together, our study reveals how changes in CCNB1IP1 expression may have contributed to the gradual evolution in primate brain.

Temperature regulates negative supercoils to modulate meiotic crossovers and chromosome organization

Crossover recombination is a hallmark of meiosis that holds the paternal and maternal chromosomes (homologs) together for their faithful segregation, while promoting genetic diversity of the progeny. The pattern of crossover is mainly controlled by the architecture of the meiotic chromosomes. Environmental factors, especially temperature, also play an important role in modulating crossovers. However, it is unclear how temperature affects crossovers. Here, we examined the distribution of budding yeast axis components (Red1, Hop1, and Rec8) and the crossover-associated Zip3 foci in detail at different temperatures, and found that both increased and decreased temperatures result in shorter meiotic chromosome axes and more crossovers. Further investigations showed that temperature changes coordinately enhanced the hyperabundant accumulation of Hop1 and Red1 on chromosomes and the number of Zip3 foci. Most importantly, temperature-induced changes in the distribution of axis proteins and Zip3 foci depend on changes in DNA negative supercoils. These results suggest that yeast meiosis senses temperature changes by increasing the level of negative supercoils to increase crossovers and modulate chromosome organization. These findings provide a new perspective on understanding the effect and mechanism of temperature on meiotic recombination and chromosome organization, with important implications for evolution and breeding.

HEI10 coarsening, chromatin and sequence polymorphism shape the plant meiotic recombination landscape

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.

Relevance, strategies, and added value of mouse models in androgenetics

BACKGROUND

Male Infertility is a prevalent condition worldwide, and a substantial fraction of cases are thought to have a genetic basis. Investigations into the responsible genes is limited experimentally, so mice have been used extensively to identify genes required for fertility and to understand their functions.

OBJECTIVES

To review the progress made in reproductive genetics based on experiments in mice, the impact upon clinical fertility genetics, and discuss how evolving technologies will continue to advance our understanding of human infertility genes.

RESULTS AND DISCUSSION

Gene knockout studies in mice have shown that several hundreds of genes are required for normal fertility and that this number is much higher in males than in females. In addition to gene discovery, the mouse is a powerful platform for functionally dissecting genetic pathways, modeling putative human infertility variants, identifying contraceptive targets, and developing in vitro gametogenesis.

CONCLUSION

These ongoing studies in mice have made an enormous contribution to our understanding of the genetics of human reproduction in the sense that the "parts list" of genes for mammalian gametogenesis is being elucidated. This would have been impossible to do in humans, and in vitro systems are not yet adequate to associate genes with andrological phenotypes, especially in the germline.

RNF212B E3 ligase is essential for crossover designation and maturation during male and female meiosis in the mouse

Meiosis, a reductional cell division, relies on precise initiation, maturation, and resolution of crossovers (COs) during prophase I to ensure the accurate segregation of homologous chromosomes during metaphase I. This process is regulated by the interplay of RING-E3 ligases such as RNF212 and HEI10 in mammals. In this study, we functionally characterized a recently identified RING-E3 ligase, RNF212B. RNF212B colocalizes and interacts with RNF212, forming foci along chromosomes from zygonema onward in a synapsis-dependent and DSB-independent manner. These consolidate into larger foci at maturing COs, colocalizing with HEI10, CNTD1, and MLH1 by late pachynema. Genetically, RNF212B foci formation depends on Rnf212 but not on Msh4, Hei10, and Cntd1, while the unloading of RNF212B at the end of pachynema is dependent on Hei10 and Cntd1. Mice lacking RNF212B, or expressing an inactive RNF212B protein, exhibit modest synapsis defects, a reduction in the localization of pro-CO factors (MSH4, TEX11, RPA, MZIP2) and absence of late CO-intermediates (MLH1). This loss of most COs by diakinesis results in mostly univalent chromosomes. Double mutants for Rnf212b and Rnf212 exhibit an identical phenotype to that of Rnf212b single mutants, while double heterozygous demonstrate a dosage-dependent reduction in CO number, indicating a functional interplay between paralogs. SUMOylome analysis of testes from Rnf212b mutants and pull-down analysis of Sumo- and Ubiquitin-tagged HeLa cells, suggest that RNF212B is an E3-ligase with Ubiquitin activity, serving as a crucial factor for CO maturation. Thus, RNF212 and RNF212B play vital, yet overlapping roles, in ensuring CO homeostasis through their distinct E3 ligase activities.

Gonadal transcriptome analysis of genes related to sex differentiation and sex development in the Pomacea canaliculata

As an invasive alien animal, Pomacea canaliculata poses a great danger to the ecology and human beings. Recently, there has been a gradual shift towards bio-friendly control. Based on the development of RNA interference and CRISPR technology as molecular regulatory techniques for pest control, it was determined if the knockout of genes related to sex differentiation in P. canaliculata could induce sterility, thereby helping in population control. However, the knowledge of sex differentiation- and development-related genes in P. canaliculata is currently lacking. Here, transcriptomic approaches were used to study the genes expressed in the two genders of P. canaliculata at various developmental stages. Gonad transcriptomes of immature or mature males and females were compared, revealing 12,063 genes with sex-specific expression, of which 6066 were male- and 5997 were female-specific. Among the latter, 581 and 235 genes were up-regulated in immature and mature females, respectively. The sex-specific expressed genes identified included GnRHR2 and TSSK3 in males and ZAR1 and WNT4 in females. Of the genes, six were involved in reproduction: CCNBLIP1, MND1, DMC1, DLC1, MRE11, and E(sev)2B. Compared to immature snail gonads, the expression of HSP90 and CDK1 was markedly reduced in gonadal. It was hypothesized that the two were associated with the development of females. These findings provided new insights into crucial genetic information on sex differentiation and development in P. canaliculata. Additionally, some candidate genes were explored, which can contribute to future studies on controlling P. canaliculata using molecular regulatory techniques.

Recent advances in mechanisms ensuring the pairing, synapsis and segregation of XY chromosomes in mice and humans

Sex chromosome aneuploidies are among the most common variations in human whole chromosome copy numbers, with an estimated prevalence in the general population of 1:400 to 1:1400 live births. Unlike whole-chromosome aneuploidies of autosomes, those of sex chromosomes, such as the 47, XXY aneuploidy that causes Klinefelter Syndrome (KS), often originate from the paternal side, caused by a lack of crossover (CO) formation between the X and Y chromosomes. COs must form between all chromosome pairs to pass meiotic checkpoints and are the product of meiotic recombination that occurs between homologous sequences of parental chromosomes. Recombination between male sex chromosomes is more challenging compared to both autosomes and sex chromosomes in females, as it is restricted within a short region of homology between X and Y, called the pseudo-autosomal region (PAR). However, in normal individuals, CO formation occurs in PAR with a higher frequency than in any other region, indicating the presence of mechanisms that promote the initiation and processing of recombination in each meiotic division. In recent years, research has made great strides in identifying genes and mechanisms that facilitate CO formation in the PAR. Here, we outline the most recent and relevant findings in this field. XY chromosome aneuploidy in humans has broad-reaching effects, contributing significantly also to Turner syndrome, spontaneous abortions, oligospermia, and even infertility. Thus, in the years to come, the identification of genes and mechanisms beyond XY aneuploidy is expected to have an impact on the genetic counseling of a wide number of families and adults affected by these disorders.

ZFP541 and KCTD19 regulate chromatin organization and transcription programs for male meiotic progression

The successful progression of meiosis prophase I requires integrating information from the structural and molecular levels. In this study, we show that ZFP541 and KCTD19 work in the same genetic pathway to regulate the progression of male meiosis and thus fertility. The Zfp541 and/or Kctd19 knockout male mice show various structural and recombination defects including detached chromosome ends, aberrant localization of chromosome axis components and recombination proteins, and globally altered histone modifications. Further analyses on RNA-seq, ChIP-seq, and ATAC-seq data provide molecular evidence for the above defects and reveal that ZFP541/KCTD19 activates the expression of many genes by repressing several major transcription repressors. More importantly, we reveal an unexpected role of ZFP541/KCTD19 in directly modulating chromatin organization. These results suggest that ZFP541/KCTD19 simultaneously regulates the transcription cascade and chromatin organization to ensure the coordinated progression of multiple events at chromosome structural and biochemical levels during meiosis prophase I.

Balanced spatiotemporal arrangements of histone H3 and H4 posttranslational modifications are necessary for meiotic prophase I chromosome organization

Dynamic nuclear architecture and chromatin organizations are the key features of the mid-prophase I in mammalian meiosis. The chromatin undergoes major changes, including meiosis-specific spatiotemporal arrangements and remodeling, the establishment of chromatin loop-axis structure, pairing, and crossing over between homologous chromosomes, any deficiencies in these events may induce genome instability, subsequently leading to failure to produce gametes and infertility. Despite the significance of chromatin structure, little is known about the location of chromatin marks and the necessity of their balance during meiosis prophase I. Here, we show a thorough cytological study of the surface-spread meiotic chromosomes of mouse spermatocytes for H3K9,14,18,23,27,36, H4K12,16 acetylation, and H3K4,9,27,36 methylation. Active acetylation and methylation marks on H3 and H4, such as H3K9ac, H3K14ac, H3K18ac, H3K36ac, H3K56ac, H4K12ac, H4K16ac, and H3K36me3 exhibited pan-nuclear localization away from heterochromatin. In comparison, repressive marks like H3K9me3 and H3K27me3 are localized to heterochromatin. Further, taking advantage of the delivery of small-molecule chemical inhibitors methotrexate (heterochromatin enhancer), heterochromatin inhibitor, anacardic acid (histone acetyltransferase inhibitor), trichostatin A (histone deacetylase inhibitor), IOX1 (JmjC demethylases inhibitor), and AZ505 (methyltransferase inhibitor) in seminiferous tubules through the rete testis route, revealed that alteration in histone modifications enhanced the centromere mislocalization, chromosome breakage, altered meiotic recombination and reduced sperm count. Specifically, IOX1 and AZ505 treatment shows severe meiotic phenotypes, including altering chromosome axis length and chromatin loop size via transcriptional regulation of meiosis-specific genes. Our findings highlight the importance of balanced chromatin modifications in meiotic prophase I chromosome organization and instability.

Control of meiotic crossover interference by a proteolytic chaperone network

Meiosis is a specialized eukaryotic division that produces genetically diverse gametes for sexual reproduction. During meiosis, homologous chromosomes pair and undergo reciprocal exchanges, called crossovers, which recombine genetic variation. Meiotic crossovers are stringently controlled with at least one obligate exchange forming per chromosome pair, while closely spaced crossovers are inhibited by interference. In Arabidopsis, crossover positions can be explained by a diffusion-mediated coarsening model, in which large, approximately evenly spaced foci of the pro-crossover E3 ligase HEI10 grow at the expense of smaller, closely spaced clusters. However, the mechanisms that control HEI10 dynamics during meiosis remain unclear. Here, through a forward genetic screen in Arabidopsis, we identified high crossover rate3 (hcr3), a dominant-negative mutant that reduces crossover interference and increases crossovers genome-wide. HCR3 encodes J3, a co-chaperone related to HSP40, which acts to target protein aggregates and biomolecular condensates to the disassembly chaperone HSP70, thereby promoting proteasomal degradation. Consistently, we show that a network of HCR3 and HSP70 chaperones facilitates proteolysis of HEI10, thereby regulating interference and the recombination landscape. These results reveal a new role for the HSP40/J3-HSP70 chaperones in regulating chromosome-wide dynamics of recombination via control of HEI10 proteolysis.

Meiotic recombination dynamics in plants with repeat-based holocentromeres shed light on the primary drivers of crossover patterning

Centromeres strongly affect (epi)genomic architecture and meiotic recombination dynamics, influencing the overall distribution and frequency of crossovers. Here we show how recombination is regulated and distributed in the holocentric plant Rhynchospora breviuscula, a species with diffused centromeres. Combining immunocytochemistry, chromatin analysis and high-throughput single-pollen sequencing, we discovered that crossover frequency is distally biased, in sharp contrast to the diffused distribution of hundreds of centromeric units and (epi)genomic features. Remarkably, we found that crossovers were abolished inside centromeric units but not in their proximity, indicating the absence of a canonical centromere effect. We further propose that telomere-led synapsis of homologues is the feature that best explains the observed recombination landscape. Our results hint at the primary influence of mechanistic features of meiotic pairing and synapsis rather than (epi)genomic features and centromere organization in determining the distally biased crossover distribution in R. breviuscula, whereas centromeres and (epi)genetic properties only affect crossover positioning locally.

RNA polymerase II pausing is essential during spermatogenesis for appropriate gene expression and completion of meiosis

Male germ cell development requires precise regulation of gene activity in a cell-type and stage-specific manner, with perturbations in gene expression during spermatogenesis associated with infertility. Here, we use steady-state, nascent and single-cell RNA sequencing strategies to comprehensively characterize gene expression across male germ cell populations, to dissect the mechanisms of gene control and provide new insights towards therapy. We discover a requirement for pausing of RNA Polymerase II (Pol II) at the earliest stages of sperm differentiation to establish the landscape of gene activity across development. Accordingly, genetic knockout of the Pol II pause-inducing factor NELF in immature germ cells blocks differentiation to spermatids. Further, we uncover unanticipated roles for Pol II pausing in the regulation of meiosis during spermatogenesis, with the presence of paused Pol II associated with double-strand break (DSB) formation, and disruption of meiotic gene expression and DSB repair in germ cells lacking NELF.

Temporal and Functional Relationship between Synaptonemal Complex Morphogenesis and Recombination during Meiosis

During prophase of meiosis I, programmed double strand breaks (DSBs) are processed into crossovers, a critical requirement for segregation of homologous chromosomes (homologs) and genome haploidization in sexually reproducing organisms. Crossovers form via homologous recombination in close temporospatial association with morphogenesis of the synaptonemal complex (SC), a proteinaceous structure that connects paired homologs along their length during the pachytene stage. Synapsis and recombination are a paradigm for the interplay between higher order chromosome structure and DNA metabolism, yet their temporal and functional relationship remains poorly understood. Probing linkage between these processes in budding yeast, we show that SC assembly is associated with a distinct threshold number of unstable D-loops. The transition from bona fide paranemic D-loops to plectonemic DSB single end invasions (SEIs) is completed during midpachynema, when the SC is fully assembled. Double Holliday junctions (dHJs) form at the time of desynapsis and are resolved into crossovers during diplonema. The SC central element component Zip1 shepherds recombination through three transitions, including DSB first end strand exchange and second end capture, as well as dHJ resolution. Zip1 mediates SEI formation independent of its polymerization whereas precocious Zip1 assembly interferes with double Holliday junction resolution. Together, our findings indicate that the synaptonemal complex controls recombination while assembled but also beyond its disassembly, possibly by establishing spatial constraints at recombination sites.

The RING Domain of Rice HEI10 is Essential for Male, But Not Female Fertility

HEI10 is a conserved E3 ubiquitin ligase involved in crossover formation during meiosis, and is thus essential for both male and female gamete development. Here, we have discovered a novel allele of HEI10 in rice that produces a truncated HEI10 protein missing its N-terminal RING domain, namely sh1 (shorter hei10 1). Unlike previously reported hei10 null alleles that are completely sterile, sh1 exhibits complete male sterility but retains partial female fertility. The causative sh1 mutation is a 76 kb inversion between OsFYVE4 and HEI10, which breaks the integrity of both genes. Allelic tests and complementation assays revealed that the gamete developmental defects of sh1 were caused by disruption of HEI10. Further studies demonstrated that short HEI10 can correctly localise to the nucleus, where it could interact with other proteins that direct meiosis; expressing short HEI10 in hei10 null lines partially restores female fertility. Our data reveal an intriguing mutant allele of HEI10 with differential effects on male and female fertility, providing a new tool to explore similarities and differences between male and female meiosis.

HEI10 is subject to phase separation and mediates RPA1a degradation during meiotic interference-sensitive crossover formation

Reciprocal exchanges of DNA between homologous chromosomes during meiosis, or crossovers (COs), shuffle genetic information in gametes and progeny. In many eukaryotes, the majority of COs (class I COs) are sensitive to a phenomenon called interference, which influences the occurrence of closely spaced double COs. Class I COs depend on a group of factors called ZMM (Zip, Msh, Mer) proteins including HEI10 (Human Enhancer of Invasion-10). However, how these proteins are recruited to class I CO sites is unclear. Here, we show that HEI10 forms foci on chromatin via a liquid-liquid phase separation (LLPS) mechanism that relies on residue Ser70. A HEI10S70F allele results in LLPS failure and a defect in class I CO formation. We further used immunoprecipitation-mass spectrometry to identify RPA1a (Replication Protein A 1) as a HEI10 interacting protein. Surprisingly, we find that RPA1a also undergoes phase separation and its ubiquitination and degradation are directly regulated by HEI10. We also show that HEI10 is required for the condensation of other class I CO factors. Thus, our results provide mechanistic insight into how meiotic class I CO formation is controlled by HEI10 coupling LLPS and ubiquitination.

Meiosis: Dances Between Homologs

The raison d'être of meiosis is shuffling of genetic information via Mendelian segregation and, within individual chromosomes, by DNA crossing-over. These outcomes are enabled by a complex cellular program in which interactions between homologous chromosomes play a central role. We first provide a background regarding the basic principles of this program. We then summarize the current understanding of the DNA events of recombination and of three processes that involve whole chromosomes: homolog pairing, crossover interference, and chiasma maturation. All of these processes are implemented by direct physical interaction of recombination complexes with underlying chromosome structures. Finally, we present convergent lines of evidence that the meiotic program may have evolved by coupling of this interaction to late-stage mitotic chromosome morphogenesis.

ATF7IP2, a meiosis-specific partner of SETDB1, is required for proper chromosome remodeling and crossover formation during spermatogenesis

Meiotic crossovers are required for the faithful segregation of homologous chromosomes and to promote genetic diversity. However, it is unclear how crossover formation is regulated, especially on the XY chromosomes, which show a homolog only at the tiny pseudoautosomal region. Here, we show that ATF7IP2 is a meiosis-specific ortholog of ATF7IP and a partner of SETDB1. In the absence of ATF7IP2, autosomes show increased axis length and more crossovers; however, many XY chromosomes lose the obligatory crossover, although the overall XY axis length is also increased. Additionally, meiotic DNA double-strand break formation/repair may also be affected by altered histone modifications. Ultimately, spermatogenesis is blocked, and male mice are infertile. These findings suggest that ATF7IP2 constraints autosomal axis length and crossovers on autosomes; meanwhile, it also modulates XY chromosomes to establish meiotic sex chromosome inactivation for cell-cycle progression and to ensure XY crossover formation during spermatogenesis.

A novel recombination protein C12ORF40/REDIC1 is required for meiotic crossover formation

During meiosis, at least one crossover must occur per homologous chromosome pair to ensure normal progression of meiotic division and accurate chromosome segregation. However, the mechanism of crossover formation is not fully understood. Here, we report a novel recombination protein, C12ORF40/REDIC1, essential for meiotic crossover formation in mammals. A homozygous frameshift mutation in C12orf40 (c.232_233insTT, p.Met78Ilefs*2) was identified in two infertile men with meiotic arrest. Spread mouse spermatocyte fluorescence immunostaining showed that REDIC1 forms discrete foci between the paired regions of homologous chromosomes depending on strand invasion and colocalizes with MSH4 and later with MLH1 at the crossover sites. Redic1 knock-in (KI) mice homozygous for mutation c.232_233insTT are infertile in both sexes due to insufficient crossovers and consequent meiotic arrest, which is also observed in our patients. The foci of MSH4 and TEX11, markers of recombination intermediates, are significantly reduced numerically in the spermatocytes of Redic1 KI mice. More importantly, our biochemical results show that the N-terminus of REDIC1 binds branched DNAs present in recombination intermediates, while the identified mutation impairs this interaction. Thus, our findings reveal a crucial role for C12ORF40/REDIC1 in meiotic crossover formation by stabilizing the recombination intermediates, providing prospective molecular targets for the clinical diagnosis and therapy of infertility.

Genetic dissection of crossover mutants defines discrete intermediates in mouse meiosis

Crossovers (COs), the exchange of homolog arms, are required for accurate chromosome segregation during meiosis. Studies in yeast have described the single-end invasion (SEI) intermediate: a stabilized 3' end annealed with the homolog as the first detectible CO precursor. SEIs are thought to differentiate into double Holliday junctions (dHJs) that are resolved by MutLgamma (MLH1/MLH3) into COs. Currently, we lack knowledge of early steps of mammalian CO recombination or how intermediates are differentiated in any organism. Using comprehensive analysis of recombination in thirteen different genetic conditions with varying levels of compromised CO resolution, we infer CO precursors include asymmetric SEI-like intermediates and dHJs in mouse. In contrast to yeast, MLH3 is structurally required to differentiate CO precursors into dHJs. We verify conservation of aspects of meiotic recombination and show unique features in mouse, providing mechanistic insight into CO formation.

Partial cytological diploidization of neoautotetraploid meiosis by induced cross-over rate reduction

Polyploids, which arise from whole-genome duplication events, have contributed to genome evolution throughout eukaryotes. Among plants, novel features of neopolyploids include traits that can be evolutionarily or agriculturally beneficial, such as increased abiotic stress tolerance. Thus, in addition to being interesting from an evolutionary perspective, genome duplication is also increasingly recognized as a promising crop improvement tool. However, newly formed (neo)polyploids commonly suffer from fertility problems, which have been attributed to abnormal associations among the multiple homologous chromosome copies during meiosis (multivalents). Here, we test the long-standing hypothesis that reducing meiotic cross-over number may be sufficient to limit multivalent formation, favoring diploid-like bivalent associations (cytological diploidization). To do so, we developed Arabidopsis thaliana lines with low cross-over rates by combining mutations for HEI10 and TAF4b. Double mutants showed a reduction of ~33% in cross-over numbers in diploids without compromising meiotic stability. Neopolyploids derived from the double mutant show a cross-over rate reduction of about 40% relative to wild-type neotetraploids, and groups of four homologs indeed formed fewer multivalents and more bivalents. However, we also show that the reduction in multivalents comes with the cost of a slightly increased frequency of univalents and that it does not rescue neopolyploid fertility. Thus, while our results do show that reducing cross-over rates can reduce multivalent frequency in neopolyploids, they also emphasize that there are additional factors affecting both meiotic stability and neopolyploid fertility that will need to be considered in solving the neopolyploid fertility challenge.

RNase H1 facilitates recombinase recruitment by degrading DNA-RNA hybrids during meiosis

DNA-RNA hybrids play various roles in many physiological progresses, but how this chromatin structure is dynamically regulated during spermatogenesis remains largely unknown. Here, we show that germ cell-specific knockout of Rnaseh1, a specialized enzyme that degrades the RNA within DNA-RNA hybrids, impairs spermatogenesis and causes male infertility. Notably, Rnaseh1 knockout results in incomplete DNA repair and meiotic prophase I arrest. These defects arise from the altered RAD51 and DMC1 recruitment in zygotene spermatocytes. Furthermore, single-molecule experiments show that RNase H1 promotes recombinase recruitment to DNA by degrading RNA within DNA-RNA hybrids and allows nucleoprotein filaments formation. Overall, we uncover a function of RNase H1 in meiotic recombination, during which it processes DNA-RNA hybrids and facilitates recombinase recruitment.

Dynamic regulatory phosphorylation of mouse CDK2 occurs during meiotic prophase I

During prophase I of meiosis, DNA double-strand breaks form throughout the genome, with a subset repairing as crossover events, enabling the accurate segregation of homologous chromosomes during the first meiotic division. The mechanism by which DSBs become selected to repair as crossovers is unknown, although the crossover positioning and levels in each cell indicate it is a highly regulated process. One of the proteins that localises to crossover sites is the serine/threonine cyclin-dependent kinase CDK2. Regulation of CDK2 occurs via phosphorylation at tyrosine 15 (Y15) and threonine 160 (T160) inhibiting and activating the kinase, respectively. In this study we use a combination of immunofluorescence staining on spread spermatocytes and fixed testis sections, and STA-PUT gravitational sedimentation to isolate cells at different developmental stages to further investigate the temporal phospho regulation of CDK2 during prophase I. Western blotting reveals differential levels of the two CDK2 isoforms (CDK233kDa and CDK239kDa) throughout prophase I, with inhibitory phosphorylation of CDK2 at Y15 occurring early in prophase I, localising to telomeres and diminishing as cells enter pachynema. Conversely, the activatory phosphorylation on T160 occurs later, specifically the CDK233kDa isoform, and T160 signal is detected in spermatogonia and pachytene spermatocytes, where it co-localises with the Class I crossover protein MLH3. Taken together, our data reveals intricate control of CDK2 both with regards to levels of the two CDK2 isoforms, and differential regulation via inhibitory and activatory phosphorylation.

A pathogenic variant in the uncharacterized RNF212B gene results in severe aneuploidy male infertility and repeated IVF failure

Quantitative and qualitative spermatogenic impairments are major causes of men's infertility. Although in vitro fertilization (IVF) is effective, some couples persistently fail to conceive. To identify causal variants in patients with severe male infertility factor and repeated IVF failures, we sequenced the exome of two consanguineous family members who underwent several failed IVF cycles and were diagnosed with low sperm count and motility. We identified a rare homozygous nonsense mutation in a previously uncharacterized gene, RNF212B, as the causative variant. Recurrence was identified in another unrelated, infertile patient who also faced repeated failed IVF treatments. scRNA-seq demonstrated meiosis-specific expression of RNF212B. Sequence analysis located a protein domain known to be associated with aneuploidy, which can explain multiple IVF failures. Accordingly, FISH analysis revealed a high aneuploidy rate in the patients' sperm cells and their IVF embryos. Finally, inactivation of the Drosophila orthologs significantly reduced male fertility. Given that members of the evolutionary conserved RNF212 gene family are involved in meiotic recombination and crossover maturation, our findings indicate a critical role of RNF212B in meiosis, genome stability, and in human fertility. Since recombination is completely absent in Drosophila males, our findings may indicate an additional unrelated role for the RNF212-like paralogs in spermatogenesis.

Crossover interference mechanism: New lessons from plants

Plants are the source of our understanding of several fundamental biological principles. It is well known that Gregor Mendel discovered the laws of Genetics in peas and that maize was used for the discovery of transposons by Barbara McClintock. Plant models are still useful for the understanding of general key biological concepts. In this article, we will focus on discussing the recent plant studies that have shed new light on the mysterious mechanisms of meiotic crossover (CO) interference, heterochiasmy, obligatory CO, and CO homeostasis. Obligatory CO is necessary for the equilibrated segregation of homologous chromosomes during meiosis. The tight control of the different male and female CO rates (heterochiasmy) enables both the maximization and minimization of genome shuffling. An integrative model can now predict these observed aspects of CO patterning in plants. The mechanism proposed considers the Synaptonemal Complex as a canalizing structure that allows the diffusion of a class I CO limiting factor linearly on synapsed bivalents. The coarsening of this limiting factor along the SC explains the interfering spacing between COs. The model explains the observed coordinated processes between synapsis, CO interference, CO insurance, and CO homeostasis. It also easily explains heterochiasmy just considering the different male and female SC lengths. This mechanism is expected to be conserved in other species.

The Msh5 complex shows homeostatic localization in response to DNA double-strand breaks in yeast meiosis

Meiotic crossing over is essential for the segregation of homologous chromosomes. The formation and distribution of meiotic crossovers (COs), which are initiated by the formation of double-strand break (DSB), are tightly regulated to ensure at least one CO per bivalent. One type of CO control, CO homeostasis, maintains a consistent level of COs despite fluctuations in DSB numbers. Here, we analyzed the localization of proteins involved in meiotic recombination in budding yeast xrs2 hypomorphic mutants which show different levels of DSBs. The number of cytological foci with recombinases, Rad51 and Dmc1, which mark single-stranded DNAs at DSB sites is proportional to the DSB numbers. Among the pro-CO factor, ZMM/SIC proteins, the focus number of Zip3, Mer3, or Spo22/Zip4, was linearly proportional to reduced DSBs in the xrs2 mutant. In contrast, foci of Msh5, a component of the MutSγ complex, showed a non-linear response to reduced DSBs. We also confirmed the homeostatic response of COs by genetic analysis of meiotic recombination in the xrs2 mutants and found a chromosome-specific homeostatic response of COs. Our study suggests that the homeostatic response of the Msh5 assembly to reduced DSBs was genetically distinct from that of the Zip3 assembly for CO control.

The regulation of meiotic crossover distribution: a coarse solution to a century-old mystery?

Meiotic crossovers, which are exchanges of genetic material between homologous chromosomes, are more evenly and distantly spaced along chromosomes than expected by chance. This is because the occurrence of one crossover reduces the likelihood of nearby crossover events - a conserved and intriguing phenomenon called crossover interference. Although crossover interference was first described over a century ago, the mechanism allowing coordination of the fate of potential crossover sites half a chromosome away remains elusive. In this review, we discuss the recently published evidence supporting a new model for crossover patterning, coined the coarsening model, and point out the missing pieces that are still needed to complete this fascinating puzzle.

Coarsening dynamics can explain meiotic crossover patterning in both the presence and absence of the synaptonemal complex

The shuffling of genetic material facilitated by meiotic crossovers is a critical driver of genetic variation. Therefore, the number and positions of crossover events must be carefully controlled. In Arabidopsis, an obligate crossover and repression of nearby crossovers on each chromosome pair are abolished in mutants that lack the synaptonemal complex (SC), a conserved protein scaffold. We use mathematical modelling and quantitative super-resolution microscopy to explore and mechanistically explain meiotic crossover pattering in Arabidopsis lines with full, incomplete, or abolished synapsis. For zyp1 mutants, which lack an SC, we develop a coarsening model in which crossover precursors globally compete for a limited pool of the pro-crossover factor HEI10, with dynamic HEI10 exchange mediated through the nucleoplasm. We demonstrate that this model is capable of quantitatively reproducing and predicting zyp1 experimental crossover patterning and HEI10 foci intensity data. Additionally, we find that a model combining both SC- and nucleoplasm-mediated coarsening can explain crossover patterning in wild-type Arabidopsis and in pch2 mutants, which display partial synapsis. Together, our results reveal that regulation of crossover patterning in wild-type Arabidopsis and SC-defective mutants likely acts through the same underlying coarsening mechanism, differing only in the spatial compartments through which the pro-crossover factor diffuses.

The sodium new houttuyfonate suppresses NSCLC via activating pyroptosis through TCONS-14036/miR-1228-5p/PRKCDBP pathway

Several studies have suggested the potential value of Houttuynia cordata as a therapeutic agent in lung cancer, but direct evidence is still lacking. The study aimed to determine the regulatory impact of a major H. cordata constituent derivative (sodium new houttuyfonate [SNH]) on lncRNA networks in non-small cell lung cancer (NSCLC) to identify new potential therapeutic targets. After exposing NSCLC cells to SNH, we analysed the following: cell death (via flow cytometry, TUNEL and ASC speck formation assays), immune factors (via ELISA), gene transcription (via RT-qPCR), subcellular localisation (via FISH), gene-gene and gene-protein interactions (via dual-luciferase reporter and RNA immunoprecipitation assays, respectively) and protein expression and distribution (via western blotting and immunocytochemistry or immunohistochemistry). In addition, statistical analysis (via one-way ANOVA or unpaired t-tests) was performed. Exposure to SNH promoted NSCLC cell pyroptosis, concomitant with significant up-regulation of TCONS-14036, a novel lncRNA. Mechanistic research demonstrated that TCONS-14036 functions as a competing endogenous (ce)RNA by sequestering microRNA (miR)-1228-5p, thereby up-regulating PRKCDBP-encoding transcript levels. Indeed, PRKCDBP promoted pyroptosis by activating the NLRP3 inflammasome, resulting in CASP1, IL-1β and GSDMD cleavage. Our findings elucidate the potential molecular mechanisms underlying the ability of SNH to suppress NSCLC growth through activation of pyroptosis via the TCONS-14036/miR-1228-5p/PRKCDBP pathway. Thus, we identify a new potential therapeutic targets for NSCLC.

Chromosome architecture and homologous recombination in meiosis

Meiocytes organize higher-order chromosome structures comprising arrays of chromatin loops organized at their bases by linear axes. As meiotic prophase progresses, the axes of homologous chromosomes align and synapse along their lengths to form ladder-like structures called synaptonemal complexes (SCs). The entire process of meiotic recombination, from initiation via programmed DNA double-strand breaks (DSBs) to completion of DSB repair with crossover or non-crossover outcomes, occurs in the context of chromosome axes and SCs. These meiosis-specific chromosome structures provide specialized environments for the regulation of DSB formation and crossing over. In this review, we summarize insights into the importance of chromosome architecture in the regulation of meiotic recombination, focusing on cohesin-mediated axis formation, DSB regulation via tethered loop-axis complexes, inter-homolog template bias facilitated by axial proteins, and crossover regulation in the context of the SCs. We also discuss emerging evidence that the SUMO and the ubiquitin-proteasome system function in the organization of chromosome structure and regulation of meiotic recombination.

Genetic control of meiosis surveillance mechanisms in mammals

Meiosis is a specialized cell division that generates haploid gametes and is critical for successful sexual reproduction. During the extended meiotic prophase I, homologous chromosomes progressively pair, synapse and desynapse. These chromosomal dynamics are tightly integrated with meiotic recombination (MR), during which programmed DNA double-strand breaks (DSBs) are formed and subsequently repaired. Consequently, parental chromosome arms reciprocally exchange, ultimately ensuring accurate homolog segregation and genetic diversity in the offspring. Surveillance mechanisms carefully monitor the MR and homologous chromosome synapsis during meiotic prophase I to avoid producing aberrant chromosomes and defective gametes. Errors in these critical processes would lead to aneuploidy and/or genetic instability. Studies of mutation in mouse models, coupled with advances in genomic technologies, lead us to more clearly understand how meiosis is controlled and how meiotic errors are linked to mammalian infertility. Here, we review the genetic regulations of these major meiotic events in mice and highlight our current understanding of their surveillance mechanisms. Furthermore, we summarize meiotic prophase genes, the mutations that activate the surveillance system leading to meiotic prophase arrest in mouse models, and their corresponding genetic variants identified in human infertile patients. Finally, we discuss their value for the diagnosis of causes of meiosis-based infertility in humans.

Identification PMS1 and PMS2 as potential meiotic substrates of CDK2 activity

Cyclin dependent-kinase 2 (CDK2) plays important functions during the mitotic cell cycle and also facilitates several key events during germ cell development. The majority of CDK2's known meiotic functions occur during prophase of the first meiotic division. Here, CDK2 is involved in the regulation of meiotic transcription, the pairing of homologous chromosomes, and the maturation of meiotic crossover sites. Despite that some of the CDK2 substrates are known, few of them display functions in meiosis. Here, we investigate potential meiotic CDK2 substrates using in silico and in vitro approaches. We find that CDK2 phosphorylates PMS2 at Thr337, PMS1 at Thr331, and MLH1 in vitro. Phosphorylation of PMS2 affects its interaction with MLH1 to some degree. In testis extracts from mice lacking Cdk2, there are changes in expression of PMS2, MSH2, and HEI10, which may be reflective of the loss of CDK2 phosphorylation. Our work has uncovered a few CDK2 substrates with meiotic functions, which will have to be verified in vivo. A better understanding of the CDK2 substrates will help us to gain deeper insight into the functions of this universal kinase.

Cyclins and CDKs in the regulation of meiosis-specific events

How eukaryotic cells control their duplication is a fascinating example of how a biological system self-organizes specific activities to temporally order cellular events. During cell cycle progression, the cellular level of CDK (Cyclin-Dependent Kinase) activity temporally orders the different cell cycle phases, ensuring that DNA replication occurs prior to segregation into two daughter cells. CDK activity requires the binding of a regulatory subunit (cyclin) to the core kinase, and both CDKs and cyclins are well conserved throughout evolution from yeast to humans. As key regulators, they coordinate cell cycle progression with metabolism, DNA damage, and cell differentiation. In meiosis, the special cell division that ensures the transmission of genetic information from one generation to the next, cyclins and CDKs have acquired novel functions to coordinate meiosis-specific events such as chromosome architecture, recombination, and synapsis. Interestingly, meiosis-specific cyclins and CDKs are common in evolution, some cyclins seem to have evolved to acquire CDK-independent functions, and even some CDKs associate with a non-cyclin partner. We will review the functions of these key regulators in meiosis where variation has specially flourished.

Role of SUMOylation in Neurodegenerative Diseases

Neurodegenerative diseases (NDDs) are irreversible, progressive diseases with no effective treatment. The hallmark of NDDs is the aggregation of misfolded, modified proteins, which impair neuronal vulnerability and cause brain damage. The loss of synaptic connection and the progressive loss of neurons result in cognitive defects. Several dysregulated proteins and overlapping molecular mechanisms contribute to the pathophysiology of NDDs. Post-translational modifications (PTMs) are essential regulators of protein function, trafficking, and maintaining neuronal hemostasis. The conjugation of a small ubiquitin-like modifier (SUMO) is a reversible, dynamic PTM required for synaptic and cognitive function. The onset and progression of neurodegenerative diseases are associated with aberrant SUMOylation. In this review, we have summarized the role of SUMOylation in regulating critical proteins involved in the onset and progression of several NDDs.

Joint control of meiotic crossover patterning by the synaptonemal complex and HEI10 dosage

Meiotic crossovers are limited in number and are prevented from occurring close to each other by crossover interference. In many species, crossover number is subject to sexual dimorphism, and a lower crossover number is associated with shorter chromosome axes lengths. How this patterning is imposed remains poorly understood. Here, we show that overexpression of the Arabidopsis pro-crossover protein HEI10 increases crossovers but maintains some interference and sexual dimorphism. Disrupting the synaptonemal complex by mutating ZYP1 also leads to an increase in crossovers but, in contrast, abolishes interference and disrupts the link between chromosome axis length and crossovers. Crucially, combining HEI10 overexpression and zyp1 mutation leads to a massive and unprecedented increase in crossovers. These observations support and can be predicted by, a recently proposed model in which HEI10 diffusion along the synaptonemal complex drives a coarsening process leading to well-spaced crossover-promoting foci, providing a mechanism for crossover patterning.

During meiosis, the number and distribution of crossovers (COs) are tightly controlled, but the mechanistic basis of this control is unclear. Here, by combining experimental data and mathematical modeling, the study advocates a CO patterning model via coarsening through the diffusion of HEI10 along the synaptonemal complex.

Negative supercoils regulate meiotic crossover patterns in budding yeast

Interference exists ubiquitously in many biological processes. Crossover interference patterns meiotic crossovers, which are required for faithful chromosome segregation and evolutionary adaption. However, what the interference signal is and how it is generated and regulated is unknown. We show that yeast top2 alleles which cannot bind or cleave DNA accumulate a higher level of negative supercoils and show weaker interference. However, top2 alleles which cannot religate the cleaved DNA or release the religated DNA accumulate less negative supercoils and show stronger interference. Moreover, the level of negative supercoils is negatively correlated with crossover interference strength. Furthermore, negative supercoils preferentially enrich at crossover-associated Zip3 regions before the formation of meiotic DNA double-strand breaks, and regions with more negative supercoils tend to have more Zip3. Additionally, the strength of crossover interference and homeostasis change coordinately in mutants. These findings suggest that the accumulation and relief of negative supercoils pattern meiotic crossovers.

Role of EXO1 nuclease activity in genome maintenance, the immune response and tumor suppression in Exo1D173A mice

DNA damage response pathways rely extensively on nuclease activity to process DNA intermediates. Exonuclease 1 (EXO1) is a pleiotropic evolutionary conserved DNA exonuclease involved in various DNA repair pathways, replication, antibody diversification, and meiosis. But, whether EXO1 facilitates these DNA metabolic processes through its enzymatic or scaffolding functions remains unclear. Here, we dissect the contribution of EXO1 enzymatic versus scaffolding activity by comparing Exo1DA/DA mice expressing a proven nuclease-dead mutant form of EXO1 to entirely EXO1-deficient Exo1-/- and EXO1 wild type Exo1+/+ mice. We show that Exo1DA/DA and Exo1-/- mice are compromised in canonical DNA repair processing, suggesting that the EXO1 enzymatic role is important for error-free DNA mismatch and double-strand break repair pathways. However, in non-canonical repair pathways, EXO1 appears to have a more nuanced function. Next-generation sequencing of heavy chain V region in B cells showed the mutation spectra of Exo1DA/DA mice to be intermediate between Exo1+/+ and Exo1-/- mice, suggesting that both catalytic and scaffolding roles of EXO1 are important for somatic hypermutation. Similarly, while overall class switch recombination in Exo1DA/DA and Exo1-/- mice was comparably defective, switch junction analysis suggests that EXO1 might fulfill an additional scaffolding function downstream of class switching. In contrast to Exo1-/- mice that are infertile, meiosis progressed normally in Exo1DA/DA and Exo1+/+ cohorts, indicating that a structural but not the nuclease function of EXO1 is critical for meiosis. However, both Exo1DA/DA and Exo1-/- mice displayed similar mortality and cancer predisposition profiles. Taken together, these data demonstrate that EXO1 has both scaffolding and enzymatic functions in distinct DNA repair processes and suggest a more composite and intricate role for EXO1 in DNA metabolic processes and disease.

Arabidopsis HEAT SHOCK FACTOR BINDING PROTEIN is required to limit meiotic crossovers and HEI10 transcription

The number of meiotic crossovers is tightly controlled and most depend on pro-crossover ZMM proteins, such as the E3 ligase HEI10. Despite the importance of HEI10 dosage for crossover formation, how HEI10 transcription is controlled remains unexplored. In a forward genetic screen using a fluorescent crossover reporter in Arabidopsis thaliana, we identify heat shock factor binding protein (HSBP) as a repressor of HEI10 transcription and crossover numbers. Using genome-wide crossover mapping and cytogenetics, we show that hsbp mutations or meiotic HSBP knockdowns increase ZMM-dependent crossovers toward the telomeres, mirroring the effects of HEI10 overexpression. Through RNA sequencing, DNA methylome, and chromatin immunoprecipitation analysis, we reveal that HSBP is required to repress HEI10 transcription by binding with heat shock factors (HSFs) at the HEI10 promoter and maintaining DNA methylation over the HEI10 5' untranslated region. Our findings provide insights into how the temperature response regulator HSBP restricts meiotic HEI10 transcription and crossover number by attenuating HSF activity.

Signalling mechanisms and cellular functions of SUMO

Sumoylation is an essential post-translational modification that is catalysed by a small number of modifying enzymes but regulates thousands of target proteins in a dynamic manner. Small ubiquitin-like modifiers (SUMOs) can be attached to target proteins as one or more monomers or in the form of polymers of different types. Non-covalent readers recognize SUMO-modified proteins via SUMO interaction motifs. SUMO simultaneously modifies groups of functionally related proteins to regulate predominantly nuclear processes, including gene expression, the DNA damage response, RNA processing, cell cycle progression and proteostasis. Recent progress has increased our understanding of the cellular and pathophysiological roles of SUMO modifications, extending their functions to the regulation of immunity, pluripotency and nuclear body assembly in response to oxidative stress, which partly occurs through the recently characterized mechanism of liquid-liquid phase separation. Such progress in understanding the roles and regulation of sumoylation opens new avenues for the targeting of SUMO to treat disease, and indeed the first drug blocking sumoylation is currently under investigation in clinical trials as a possible anticancer agent.

A Homozygous Loss-of-Function Mutation in MSH5 Abolishes MutSγ Axial Loading and Causes Meiotic Arrest in NOA-Affected Individuals

Non-obstructive azoospermia (NOA), characterized by spermatogenesis failure and the absence of sperm in ejaculation, is the most severe form of male infertility. However, the etiology and pathology between meiosis-associated monogenic alterations and human NOA remain largely unknown. A homozygous MSH5 mutation (c.1126del) was identified from two idiopathic NOA patients in the consanguineous family. This mutation led to the degradation of MSH5 mRNA and abolished chromosome axial localization of MutSγ in spermatocytes from the affected males. Chromosomal spreading analysis of the patient's meiotic prophase I revealed that the meiosis progression was arrested at a zygotene-like stage with extensive failure of homologous synapsis and DSB repair. Therefore, our study demonstrates that the MSH5 c.1126del could cause meiotic recombination failure and lead to human infertility, improving the genetic diagnosis of NOA clinically. Furthermore, the study of human spermatocytes elucidates the meiosis defects caused by MSH5 variant, and reveals a conserved and indispensable role of MutSγ in human synapsis and meiotic recombination, which have not previously been well-described.

Robust designation of meiotic crossover sites by CDK-2 through phosphorylation of the MutSγ complex

Crossover formation is essential for proper segregation of homologous chromosomes during meiosis. Here, we show that Caenorhabditis elegans cyclin-dependent kinase 2 (CDK-2) partners with cyclin-like protein COSA-1 to promote crossover formation by promoting conversion of meiotic double-strand breaks into crossover–specific recombination intermediates. Further, we identify MutSγ component MSH-5 as a CDK-2 phosphorylation target. MSH-5 has a disordered C-terminal tail that contains 13 potential CDK phosphosites and is required to concentrate crossover–promoting proteins at recombination sites. Phosphorylation of the MSH-5 tail appears dispensable in a wild-type background, but when MutSγ activity is partially compromised, crossover formation and retention of COSA-1 at recombination sites are exquisitely sensitive to phosphosite loss. Our data support a model in which robustness of crossover designation reflects a positive feedback mechanism involving CDK-2–mediated phosphorylation and scaffold-like properties of the MSH5 C-terminal tail, features that combine to promote full recruitment and activity of crossover–promoting complexes.

MEIOK21 regulates oocyte quantity and quality via modulating meiotic recombination

The reproductive life span of females is largely determined by the number and quality of oocytes. Previously, we identified MEIOK21 as a meiotic recombination regulator required for male fertility. Here, we characterize the important roles of MEIOK21 in regulating female meiosis and oocyte number and quality. MEIOK21 localizes at recombination sites as a component of recombination bridges in oogenesis like in spermatogenesis. Meiok21^-/- female mice show subfertility. Consistently, the size of the primordial follicle pool in Meiok21^-/- females is only ~40% of wild-type females because a great number of oocytes with defects in meiotic recombination and/or synapsis are eliminated. Furthermore, the numbers of primordial and growing follicles show a more marked decrease in an age-dependent manner compared with wild-type females. Further analysis shows Meiok21^-/- oocytes also have reduced rates of germinal vesicle breakdown and the first polar body extrusion when cultured in vitro, indicating poor oocyte quality. Additionally, Meiok21^-/- oocytes have more chromosomes bearing a single distally localized crossover (chiasmata), suggesting a possible defect in crossover maturation. Taken together, our findings indicate critical roles for MEIOK21 in ensuring the number and quality of oocytes in the follicles.