Arabidopsis FIN219/JAR1 interacts with phytochrome A under far-red light and jasmonates in regulating hypocotyl elongation via a functional demand manner.

Integration of light and phytohormones is essential for plant growth and development. FAR-RED INSENSITIVE 219 (FIN219)/JASMONATE RESISTANT 1 (JAR1) participates in phytochrome A (phyA)-mediated far-red (FR) light signaling in Arabidopsis and is a jasmonate (JA)-conjugating enzyme for the generation of an active JA-isoleucine. Accumulating evidence indicates that FR and JA signaling integrate with each other. However, the molecular mechanisms underlying their interaction remain largely unknown. Here, the phyA mutant was hypersensitive to JA. The double mutant fin219-2phyA-211 showed a synergistic effect on seedling development under FR light. Further evidence revealed that FIN219 and phyA antagonized with each other in a mutually functional demand to modulate hypocotyl elongation and expression of light- and JA-responsive genes. Moreover, FIN219 interacted with phyA under prolonged FR light, and MeJA could enhance their interaction with CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) in the dark and FR light. FIN219 and phyA interaction occurred mainly in the cytoplasm, and they regulated their mutual subcellular localization under FR light. Surprisingly, the fin219-2 mutant abolished the formation of phyA nuclear bodies under FR light. Overall, these data identified a vital mechanism of phyA-FIN219-COP1 association in response to FR light, and MeJA may allow the photoactivated phyA to trigger photomorphogenic responses.

M1AP interacts with the mammalian ZZS complex and promotes male meiotic recombination.

Following meiotic recombination, each pair of homologous chromosomes acquires at least one crossover, which ensures accurate chromosome segregation and allows reciprocal exchange of genetic information. Recombination failure often leads to meiotic arrest, impairing fertility, but the molecular basis of recombination remains elusive. Here, we report a homozygous M1AP splicing mutation (c.1074 + 2T > C) in patients with severe oligozoospermia owing to meiotic metaphase I arrest. The mutation abolishes M1AP foci on the chromosome axes, resulting in decreased recombination intermediates and crossovers in male mouse models. M1AP interacts with the mammalian ZZS (an acronym for yeast proteins Zip2-Zip4-Spo16) complex components, SHOC1, TEX11, and SPO16. M1AP localizes to chromosomal axes in a SPO16-dependent manner and colocalizes with TEX11. Ablation of M1AP does not alter SHOC1 localization but reduces the recruitment of TEX11 to recombination intermediates. M1AP shows cytoplasmic localization in fetal oocytes and is dispensable for fertility and crossover formation in female mice. Our study provides the first evidence that M1AP acts as a copartner of the ZZS complex to promote crossover formation and meiotic progression in males.

Homozygous mutations in C14orf39/SIX6OS1 cause non-obstructive azoospermia and premature ovarian insufficiency in humans.

Human infertility is a multifactorial disease that affects 8%-12% of reproductive-aged couples worldwide. However, the genetic causes of human infertility are still poorly understood. Synaptonemal complex (SC) is a conserved tripartite structure that holds homologous chromosomes together and plays an indispensable role in the meiotic progression. Here, we identified three homozygous mutations in the SC coding gene C14orf39/SIX6OS1 in infertile individuals from different ethnic populations by whole-exome sequencing (WES). These mutations include a frameshift mutation (c.204_205del [p.His68Glnfs∗2]) from a consanguineous Pakistani family with two males suffering from non-obstructive azoospermia (NOA) and one female diagnosed with premature ovarian insufficiency (POI) as well as a nonsense mutation (c.958G>T [p.Glu320∗]) and a splicing mutation (c.1180-3C>G) in two unrelated Chinese men (individual P3907 and individual P6032, respectively) with meiotic arrest. Mutations in C14orf39 resulted in truncated proteins that retained SYCE1 binding but exhibited impaired polycomplex formation between C14ORF39 and SYCE1. Further cytological analyses of meiosis in germ cells revealed that the affected familial males with the C14orf39 frameshift mutation displayed complete asynapsis between homologous chromosomes, while the affected Chinese men carrying the nonsense or splicing mutation showed incomplete synapsis. The phenotypes of NOA and POI in affected individuals were well recapitulated by Six6os1 mutant mice carrying an analogous mutation. Collectively, our findings in humans and mice highlight the conserved role of C14ORF39/SIX6OS1 in SC assembly and indicate that the homozygous mutations in C14orf39/SIX6OS1 described here are responsible for infertility of these affected individuals, thus expanding our understanding of the genetic basis of human infertility.

Nuclear translocation of MTL5 from cytoplasm requires its direct interaction with LIN9 and is essential for male meiosis and fertility.

Meiosis is essential for the generation of gametes and sexual reproduction, yet the factors and underlying mechanisms regulating meiotic progression remain largely unknown. Here, we showed that MTL5 translocates into nuclei of spermatocytes during zygotene-pachytene transition and ensures meiosis advances beyond pachytene stage. MTL5 shows strong interactions with MuvB core complex components, a well-known transcriptional complex regulating mitotic progression, and the zygotene-pachytene transition of MTL5 is mediated by its direct interaction with the component LIN9, through MTL5 C-terminal 443-475 residues. Male Mtl5c-mu/c-mu mice expressing the truncated MTL5 (p.Ser445Arg fs*3) that lacks the interaction with LIN9 and is detained in cytoplasm showed male infertility and spermatogenic arrest at pachytene stage, same as that of Mtl5 knockout mice, indicating that the interaction with LIN9 is essential for the nuclear translocation and function of MTL5 during meiosis. Our data demonstrated MTL5 translocates into nuclei during the zygotene-pachytene transition to initiate its function along with the MuvB core complex in pachytene spermatocytes, highlighting a new mechanism regulating the progression of male meiosis.

APYRASE1/2 mediate red light-induced de-etiolation growth in Arabidopsis seedlings.

In etiolated seedlings, red light (R) activates phytochrome and initiates signals that generate major changes at molecular and physiological levels. These changes include inhibition of hypocotyl growth and promotion of the growth of primary roots, apical hooks, and cotyledons. An earlier report showed that the sharp decrease in hypocotyl growth rapidly induced by R was accompanied by an equally rapid decrease in the transcript and protein levels of two closely related apyrases (APYs; nucleoside triphosphate-diphosphohydrolases) in Arabidopsis (Arabidopsis thaliana), APY1 and APY2, enzymes whose expression alters auxin transport and growth in seedlings. Here, we report that single knockouts of either APY inhibit R-induced promotion of the growth of primary roots, apical hooks, and cotyledons, and RNAi-induced suppression of APY1 expression in the background of apy2 inhibits R-induced apical hook opening. When R-irradiated primary roots and apical hook-cotyledons began to show a gradual increase in their growth relative to dark controls, they concurrently showed increased levels of APY protein, but in hook-cotyledon tissue, this occurred without parallel increases in their transcripts. In wild-type seedlings whose root growth is suppressed by the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the R-induced increased APY expression in roots was also inhibited. In unirradiated plants, the constitutive expression of APY2 promoted both hook opening and changes in the transcript abundance of Small Auxin Upregulated RNA (SAUR), SAUR17 and SAUR50 that help mediate de-etiolation. These results provide evidence that the expression of APY1/APY2 is regulated by R and that APY1/APY2 participate in the signaling pathway by which phytochrome induces differential growth changes in different tissues of etiolated seedlings.

Identification of pathogenic mutations from nonobstructive azoospermia patients†.

It is estimated that approximately 25% of nonobstructive azoospermia (NOA) cases are caused by single genetic anomalies, including chromosomal aberrations and gene mutations. The identification of these mutations in NOA patients has always been a research hot spot in the area of human infertility. However, compared with more than 600 genes reported to be essential for fertility in mice, mutations in approximately 75 genes have been confirmed to be pathogenic in patients with male infertility, in which only 14 were identified from NOA patients. The small proportion suggested that there is much room to improve the methodology of mutation screening and functional verification. Fortunately, recent advances in whole exome sequencing and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 have greatly promoted research on the etiology of human infertility and made improvements possible. In this review, we have summarized the pathogenic mutations found in NOA patients and the efforts we have made to improve the efficiency of mutation screening from NOA patients and functional verification with the application of new technologies.

Biallelic HFM1 variants cause non-obstructive azoospermia with meiotic arrest in humans by impairing crossover formation to varying degrees.

STUDY QUESTION: Do variants in helicase for meiosis 1 (HFM1) account for male infertility in humans? SUMMARY ANSWER: Biallelic variants in HFM1 cause human male infertility owing to non-obstructive azoospermia (NOA) with impaired crossover formation and meiotic metaphase I (MMI) arrest. WHAT IS KNOWN ALREADY: HFM1 encodes an evolutionarily conserved DNA helicase that is essential for crossover formation and completion of meiosis. The null mutants of Hfm1 or its ortholog in multiple organisms displayed spermatogenic arrest at the MMI owing to deficiencies in synapsis and severe defects in crossover formation. Although HFM1 variants were found in infertile men with azoospermia or oligozoospermia, the causal relationship has not yet been established with functional evidence. STUDY DESIGN, SIZE, DURATION: A Pakistani family, having two infertile brothers born to consanguineous parents, and three unrelated Chinese men diagnosed with NOA were recruited for pathogenic variants screening. PARTICIPANTS/MATERIALS, SETTING, METHODS: All the patients were diagnosed with idiopathic NOA and, for the Chinese patients, meiotic defects were confirmed by histological analyses and/or immunofluorescence staining on testicular sections. Exome sequencing and subsequent bioinformatic analyses were performed to screen for candidate pathogenic variants. The pathogenicity of identified variants was assessed and studied in vivo in mice carrying the equivalent mutations. MAIN RESULTS AND THE ROLE OF CHANCE: Six variants (homozygous or compound heterozygous) in HFM1 were identified in the three Chinese patients with NOA and two brothers with NOA from the Pakistani family. Testicular histological analysis revealed that spermatogenesis is arrested at MMI in patients carrying the variants. Mice modeling the HFM1 variants identified in patients recapitulated the meiotic defects of patients, confirming the pathogenicity of the identified variants. These Hfm1 variants led to various reductions of HFM1 foci on chromosome axes and resulted in varying degrees of synapsis and crossover formation defects in the mutant male mice. In addition, Hfm1 mutant female mice displayed infertility or subfertility with oogenesis variously affected. LIMITATIONS, REASONS FOR CAUTION: A limitation of the current study is the small sample size. Owing to the unavailability of fresh testicular samples, the defects of synapsis and crossover formation could not be detected in spermatocytes of patients. Owing to the unavailability of antibodies, we could not quantify the impact of these variants on HFM1 protein levels. WIDER IMPLICATIONS OF THE FINDINGS: Our findings provide direct clinical and in vivo functional evidence that HFM1 variants cause male infertility in humans and also suggest that HFM1 may regulate meiotic crossover formation in a dose-dependent manner. Noticeably, our findings from mouse models showed that HFM1 variants could impair spermatogenesis and oogenesis with a varying degree of severity and might also be compatible with the production of a few spermatozoa in men and subfertility in women, extending the phenotypic spectrum of patients with HFM1 variants. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the National Natural Science Foundation of China (31890780, 32070850, 32061143006, 32000587 and 31900398) and the Fundamental Research Funds for the Central Universities (YD2070002007 and YD2070002012). The authors declare no potential conflicts of interest. TRIAL REGISTRATION NUMBER: N/A.

MOF influences meiotic expansion of H2AX phosphorylation and spermatogenesis in mice.

Three waves of H2AX phosphorylation (γH2AX) have been observed in male meiotic prophase I: the first is ATM-dependent and occurs at leptonema, while the second and third are ATR-dependent, occuring at zygonema and pachynema, respectively. The third wave of H2AX phosphorylation marks and silences unsynapsed chromosomes. Little is known about H2AX phosphorylation expands to chromatin-wide regions in spermatocytes. Here, we report that histone acetyltransferase (HAT) MOF is involved in all three waves of H2AX phosphorylation expansion. Germ cell-specific deletion of Mof in spermatocytes by Stra8-Cre (Mof cKO) caused global loss of H4K16ac. In leptotene and zygotene spermatocytes of cKO mice, the γH2AX signals were observed only along the chromosomal axes, and chromatin-wide H2AX phosphorylation was lost. In almost 40% of early-mid pachytene spermatocytes from Mof cKO mice, γH2AX and MDC1 were detected along the unsynapsed axes of the sex chromosomes, but failed to expand, which consequently caused meiotic sex chromosome inactivation (MSCI) failure. Furthermore, though RAD51 was proficiently recruited to double-strand break (DSB) sites, defects in DSB repair and crossover formation were observed in Mof cKO spermatocytes, indicating that MOF facilitates meiotic DSB repair after RAD51 recruitment. We propose that MOF regulates male meiosis and is involved in the expansion of all three waves of H2AX phosphorylation from the leptotene to pachytene stages, initiated by ATM and ATR, respectively.

Histone acetyltransferase KAT8 is essential for mouse oocyte development by regulating reactive oxygen species levels.

Proper oocyte development is crucial for female fertility and requires timely and accurate control of gene expression. K (lysine) acetyltransferase 8 (KAT8), an important component of the X chromosome dosage compensation system in Drosophila, regulates gene activity by acetylating histone H4 preferentially at lysine 16. To explore the function of KAT8 during mouse oocyte development, we crossed Kat8flox/flox mice with Gdf9-Cre mice to specifically delete Kat8 in oocytes. Oocyte Kat8 deletion resulted in female infertility, with follicle development failure in the secondary and preantral follicle stages. RNA-seq analysis revealed that Kat8 deficiency in oocytes results in significant downregulation of antioxidant genes, with a consequent increase in reactive oxygen species. Intraperitoneal injection of the antioxidant N-acetylcysteine rescued defective follicle and oocyte development resulting from Kat8 deficiency. Chromatin immunoprecipitation assays indicated that KAT8 regulates antioxidant gene expression by direct binding to promoter regions. Taken together, our findings demonstrate that KAT8 is essential for female fertility by regulating antioxidant gene expression and identify KAT8 as the first histone acetyltransferase with an essential function in oogenesis.

[Synaptonemal complex: the fundamental structure of meiosis].

Meiosis is a special type of cell division to produce haploid gametes with intact genome. The behavior of homologous chromosomes during the first division (meiosis prophase I) is the most prominent feature of meiosis. During meiosis prophase I, synaptonemal complex (SC) formed between homologous chromosomes to promote the initiation and repair of programmed DNA double-strand breaks (DSBs), which is necessary for the correct recognition, pairing, recombination and separation of homologous chromosomes. In this paper, we reviewed the recent research progress on the composition and function of SC, discussed how the assembly of SC affected the repair of DSBs, and also summarized the known mutations on SC genes which were responsible for human reproductive disorders. On this basis, we also explored the future research direction of this field.

A homozygous FANCM frameshift pathogenic variant causes male infertility.

PURPOSE: Fanconi anemia (FA) genes play important roles in spermatogenesis. In mice, disruption of Fancm impairs male fertility and testicular integrity, but whether FANCM pathogenic variants (PV) similarly affect fertility in men is unknown. Here we characterize a Pakistani family having three infertile brothers, two manifesting oligoasthenospermia and one exhibiting azoospermia, born to first-cousin parents. A homozygous PV in FANCM (c.1946_1958del, p.P648Lfs*16) was found cosegregating with male infertility. Our objective is to validate that FANCM p.P648Lfs*16 is the PV causing infertility in this family. METHODS: Exome and Sanger sequencing were used for PV screening. DNA interstrand crosslink (ICL) sensitivity was assessed in lymphocytes from patients. A mouse model carrying a PV nearly equivalent to that in the patients (FancmΔC/ΔC) was generated, followed by functional analysis in spermatogenesis. RESULTS: The loss-of-function FANCM PV increased ICL sensitivity in lymphocytes of patients and FancmΔC/ΔC spermatogonia. Adult FancmΔC/ΔC mice showed spermatogenic failure, with germ cell loss in 50.2% of testicular tubules and round-spermatid maturation arrest in 43.5% of tubules. In addition, neither bone marrow failure nor cancer/tumor was detected in all the patients or adult FancmΔC/ΔC mice. CONCLUSION: These findings revealed male infertility to be a novel phenotype of human patients with a biallelic FANCM PV.

Correction: A homozygous FANCM frameshift pathogenic variant causes male infertility.

Hao Win, Hui Ma and Sajjad Hussain were incorrectly affiliated to 'Department of Radiation Oncology, The Houston Methodist Research Institute, Houston, TX 77030 USA'. These authors should only have been affiliated to 'Hefei National Laboratory for Physical Sciences at Microscale, The First Affiliated Hospital of USTC, USTC-SJH Joint Center for Human Reproduction and Genetics, The CAS Key Laboratory of Innate Immunity and Chronic Diseases, School of Life Sciences, CAS Center for Excellence in Molecular Cell Science, Collaborative Innovation Center of Genetics and Development, University of Science and Technology of China, Hefei 230027, China'. They were also not noted as contributing equally to the paper. Both these errors have now been corrected in the PDF and HTML versions of the paper.

Decreased XY recombination and disturbed meiotic prophase I progression in an infertile 48, XYY, +sSMC man.

Small supernumerary marker chromosomes (sSMCs) are structurally abnormal rare chromosomes, difficult to characterize by karyotyping, and have been associated with minor dysmorphic features, azoospermia, and recurrent miscarriages. However, sSMC with a gonosomal trisomy has never been reported. Spermatocyte spreading and immunostaining were applied to detect meiotic prophase I progression, homologous chromosome pairing, synapsis, and recombination. In all the analyzed spermatocytes of the patient, the extra Y chromosome was not detected while the sSMC was present. The recombination frequency on autosomes was not affected, while the recombination frequencies on XY chromosome was significantly lower in the patient than in the controls. The meiotic prophase I progression was disturbed with significantly increased proportion of zygotene and decreased pachytene spermatocytes in the patients as compared with the controls. These findings highlight the importance of studies on meiotic behaviors in patients with an abnormal chromosomal constitution and provide an important framework for future studies, which may elucidate the impairment caused by sSMC in mammalian meiosis and fertility.

Abnormal meiotic recombination with complex chromosomal rearrangement in an azoospermic man.

Spermatocyte spreading and immunostaining were applied to detect meiotic prophase I progression, homologous chromosome pairing, synapsis and recombination in an azoospermic reciprocal translocation 46, XY, t(5;7;9;13)(5q11;7p11;7p15;9q12;13p12) carrier. Histological examination of the haematoxylin and eosin stained testicular sections revealed reduced germ cells with no spermatids or sperm in the patient. TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end labelling assay showed apoptotic cells in testicular sections of translocation carrier. Immnunofluorescence analysis indicated the presence of an octavalent in all the pachytene spermatocytes analysed in the patient. Meiotic progression was disturbed, as an increase in zygotene (P < 0.001) and decrease in the pachytene spermatocytes (P < 0.001) were observed in the t(5;7;9;13) carrier compared with controls. It was further observed that 93% of octavalents were found partially asynapsed between homologous chromosomes. A significant decrease in the recombination frequency was observed on 5p, 5q, 7q, 9p and 13q in the translocation carrier compared with the reported controls. A significant reduction in XY recombination frequency was also found in the participants. Our results indicated that complex chromosomal rearrangements can impair synaptic integrity of translocated chromosomes, which may reduce chromosomal recombination on translocated as well as non-translocated chromosomes, a phenomenon commonly known as interchromosomal effect.

Drought and salt stress tolerance of an Arabidopsis glutathione S-transferase U17 knockout mutant are attributed to the combined effect of glutathione and abscisic acid.

Although glutathione S-transferases (GSTs) are thought to play major roles in oxidative stress metabolism, little is known about the regulatory functions of GSTs. We have reported that Arabidopsis (Arabidopsis thaliana) GLUTATHIONE S-TRANSFERASE U17 (AtGSTU17; At1g10370) participates in light signaling and might modulate various aspects of development by affecting glutathione (GSH) pools via a coordinated regulation with phytochrome A. Here, we provide further evidence to support a negative role of AtGSTU17 in drought and salt stress tolerance. When AtGSTU17 was mutated, plants were more tolerant to drought and salt stresses compared with wild-type plants. In addition, atgstu17 accumulated higher levels of GSH and abscisic acid (ABA) and exhibited hyposensitivity to ABA during seed germination, smaller stomatal apertures, a lower transpiration rate, better development of primary and lateral root systems, and longer vegetative growth. To explore how atgstu17 accumulated higher ABA content, we grew wild-type plants in the solution containing GSH and found that they accumulated ABA to a higher extent than plants grown in the absence of GSH, and they also exhibited the atgstu17 phenotypes. Wild-type plants treated with GSH also demonstrated more tolerance to drought and salt stresses. Furthermore, the effect of GSH on root patterning and drought tolerance was confirmed by growing the atgstu17 in solution containing l-buthionine-(S,R)-sulfoximine, a specific inhibitor of GSH biosynthesis. In conclusion, the atgstu17 phenotype can be explained by the combined effect of GSH and ABA. We propose a role of AtGSTU17 in adaptive responses to drought and salt stresses by functioning as a negative component of stress-mediated signal transduction pathways.

Identification of a Far-Red Light-Inducible Promoter that Exhibits Light Intensity Dependency and Reversibility in a Cyanobacterium.

As the demand for sustainable energy has increased, photoautotrophic cyanobacteria have become a popular platform for developing tools in synthetic biology. Although genetic tools are generally available for several model cyanobacteria, such tools have not yet been developed for many other strains potentially suitable for industrial applications. Additionally, most inducible promoters in cyanobacteria are controlled by chemical compounds, but adding chemicals into growth media on an industrial scale is neither cost-effective nor environmentally friendly. Although using light-controlled promoters is an alternative approach, only a cyanobacterial expression system inducible by green light has so far been described and employed for such applications. In this study, we have established a conjugation-based technique to express a reporter gene (eyfp) in the nonmodel cyanobacterium, Chlorogloeopsis fritschii PCC 9212. We also identified a promoter specifically activated by far-red light from the Far-Red Light Photoacclimation gene cluster of Leptolyngbya sp. JSC-1. This promoter, PchlFJSC1, was successfully used to drive eyfp expression. PchlFJSC1 is tightly regulated by light quality (i.e., wavelength) and leads to an approximately 30-fold increase in EYFP production when cells were exposed to far-red light. The induction level was controlled by the far-red light intensity, and induction stopped when cells were returned to visible light. This system has the potential for further applications in cyanobacteria by providing an additional choice of light wavelength to control gene expression. Collectively, this study developed a functional gene-expression system for C. fritschii PCC 9212 that can be regulated by exposing cells to far-red light.

A structure of the relict phycobilisome from a thylakoid-free cyanobacterium.

Phycobilisomes (PBS) are antenna megacomplexes that transfer energy to photosystems II and I in thylakoids. PBS likely evolved from a basic, inefficient form into the predominant hemidiscoidal shape with radiating peripheral rods. However, it has been challenging to test this hypothesis because ancestral species are generally inaccessible. Here we use spectroscopy and cryo-electron microscopy to reveal a structure of a "paddle-shaped" PBS from a thylakoid-free cyanobacterium that likely retains ancestral traits. This PBS lacks rods and specialized ApcD and ApcF subunits, indicating relict characteristics. Other features include linkers connecting two chains of five phycocyanin hexamers (CpcN) and two core subdomains (ApcH), resulting in a paddle-shaped configuration. Energy transfer calculations demonstrate that chains are less efficient than rods. These features may nevertheless have increased light absorption by elongating PBS before multilayered thylakoids with hemidiscoidal PBS evolved. Our results provide insights into the evolution and diversification of light-harvesting strategies before the origin of thylakoids.

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.

Loss-of-function variants in KCTD19 cause non-obstructive azoospermia in humans.

Azoospermia is a significant cause of male infertility, with non-obstructive azoospermia (NOA) being the most severe type of spermatogenic failure. NOA is mostly caused by congenital factors, but our understanding of its genetic causes is very limited. Here, we identified a frameshift variant (c.201_202insAC, p.Tyr68Thrfs∗17) and two nonsense variants (c.1897C>T, p.Gln633∗; c.2005C>T, p.Gln669∗) in KCTD19 (potassium channel tetramerization domain containing 19) from two unrelated infertile Chinese men and a consanguineous Pakistani family with three infertile brothers. Testicular histological analyses revealed meiotic metaphase I (MMI) arrest in the affected individuals. Mice modeling KCTD19 variants recapitulated the same MMI arrest phenotype due to severe disrupted individualization of MMI chromosomes. Further analysis showed a complete loss of KCTD19 protein in both Kctd19 mutant mouse testes and affected individual testes. Collectively, our findings demonstrate the pathogenicity of the identified KCTD19 variants and highlight an essential role of KCTD19 in MMI chromosome individualization.