Membrane fusion is an essential step in the encounter of two nuclei from sex cells-sperm and egg-in fertilization. However, aside from the involvement of two molecules, CD9 and Izumo, the mechanism of fusion remains unclear. Here, we show that spermegg fusion is mediated by vesicles containing CD9 that are released from the egg and interact with sperm. We demonstrate that the CD9 ؊/؊ eggs, which have a defective sperm-fusing ability, have impaired release of CD9-containing vesicles. We investigate the fusion-facilitating activity of CD9-containing vesicles by examining the fusion of sperm to CD9 ؊/؊ eggs with the aid of exogenous CD9-containing vesicles. Moreover, we show, by examining the fusion of sperm to CD9 ؊/؊ eggs, that hamster eggs have a similar fusing ability as mouse eggs. The CD9-containing vesicle release from unfertilized eggs provides insight into the mechanism required for fusion with sperm.

Introducing a point mutation is a fundamental method used to demonstrate the roles of particular nucleotides or amino acids in the genetic elements or proteins, and is widely used in in vitro experiments based on cultured cells and exogenously provided DNA. However, the in vivo application of this approach by modifying genomic loci is uncommon, partly due to its technical and temporal demands. This leaves many in vitro findings un-validated under in vivo conditions. We herein applied the CRISPR/Cas9 system to generate mice with point mutations in their genomes, which led to single amino acid substitutions in proteins of interest. By microinjecting gRNA, hCas9 mRNA and single-stranded donor oligonucleotides (ssODN) into mouse zygotes, we introduced defined genomic modifications in their genome with a low cost and in a short time. Both single gRNA/WT hCas9 and double nicking set-ups were effective. We also found that the distance between the modification site and gRNA target site was a significant parameter affecting the efficiency of the substitution. We believe that this is a powerful technique that can be used to examine the relevance of in vitro findings, as well as the mutations found in patients with genetic disorders, in an in vivo system.

STUDY QUESTION What were the risks with regard to the pregnancy outcomes of patients who conceived by frozen-thawed embryo transfer (FET) during a hormone replacement cycle (HRC-FET)? SUMMARY ANSWER The patients who conceived by HRC-FET had increased risks of hypertensive disorders of pregnancy (HDP) and placenta accreta and a reduced risk of gestational diabetes mellitus (GDM) in comparison to those who conceived by FET during a natural ovulatory cycle (NC-FET). WHAT IS KNOWN ALREADY Previous studies have shown that pregnancy and live-birth rates after HRC-FET and NC-FET are comparable. Little has been clarified regarding the association between endometrium preparation and other pregnancy outcomes. STUDY DESIGN, SIZE, DURATION A retrospective cohort study of patients who conceived after HRC-FET and those who conceived after NC-FET was performed based on the Japanese assisted reproductive technology registry in 2014. PARTICIPANTS/MATERIALS, SETTING, METHODS The pregnancy outcomes were compared between NC-FET (n = 29 760) and HRC-FET (n = 75 474) cycles. Multiple logistic regression analyses were performed to investigate the potential confounding factors. MAIN RESULTS AND THE ROLE OF CHANCE The pregnancy rate (32.1% vs 36.1%) and the live birth rate among pregnancies (67.1% vs 71.9%) in HRC-FET cycles were significantly lower than those in NC-FET cycles. A multiple logistic regression analysis showed that pregnancies after HRC-FET had increased odds of HDPs [adjusted odds ratio, 1.43; 95% confidence interval (CI), 1.14–1.80] and placenta accreta (adjusted odds ratio, 6.91; 95% CI, 2.87–16.66) and decreased odds for GDM (adjusted odds ratio, 0.52; 95% CI, 0.40–0.68) in comparison to pregnancies after NC-FET. LIMITATIONS, REASONS FOR CAUTION Our study was retrospective in nature, and some cases were excluded due to missing data. The implication of bias and residual confounding factors such as body mass index, alcohol consumption, and smoking habits should be considered in other observational studies. WIDER IMPLICATIONS OF THE FINDINGS Pregnancies following HRC-FET are associated with higher risks of HDPs and placenta accreta and a lower risk of GDM. The association between the endometrium preparation method and obstetrical complication merits further attention. STUDY FUNDING/COMPETING INTEREST(S) No funding was obtained for this work. The authors declare no conflicts of interest in association with the present study. TRIAL REGISTRATION NUMBER Not applicable.

The role of monogenic mutations in the development of 46,XX testicular/ovotesticular disorders of sex development (DSD) remains speculative. Although mutations in NR5A1 are known to cause 46,XY gonadal dysgenesis and 46,XX ovarian insufficiency, such mutations have not been implicated in testicular development of 46,XX gonads. Here, we identified identical NR5A1 mutations in two unrelated Japanese patients with 46,XX testicular/ovotesticular DSD. The p.Arg92Trp mutation was absent from the clinically normal mothers and from 200 unaffected Japanese individuals. In silico analyses scored p.Arg92Trp as probably pathogenic. In vitro assays demonstrated that compared with wild-type NR5A1, the mutant protein was less sensitive to NR0B1-induced suppression on the SOX9 enhancer element. Other sequence variants found in the patients were unlikely to be associated with the phenotype. The results raise the possibility that specific mutations in NR5A1 underlie testicular development in genetic females.

SummaryWhen a sperm and oocyte unite into one cell upon fertilization, membranous fusion between the sperm and oocyte occurs. In mice, Izumo1 and a tetraspanin molecule CD9 are required for sperm-oocyte fusion as one of the oocyte factors, and another tetraspanin molecule CD81 is also thought to involve in this process. Since these two tetraspanins often form a complex upon cell-cell interaction, it is probable that such a complex is also formed in sperm-oocyte interaction; however, this possibility is still under debate among researchers. Here we assessed this problem using mouse oocytes. Immunocytochemical analysis demonstrated that both CD9 and CD81 were widely distributed outside the oocyte cell membrane, but these molecules were separate, forming bilayers, confirmed by immunobiochemical analysis. Electron-microscopic analysis revealed the presence of CD9- or CD81-incorporated extracellular structures in those bilayers. Finally, microinjection of in vitro-synthesized RNA showed that CD9 reversed a fusion defect in CD81-deficient oocytes in addition to CD9-deficient oocytes, but CD81 failed in both oocytes. These results suggest that both CD9 and CD81 independently work upon sperm-oocyte fusion as extracellular components.

Although mastermind-like domain containing 1 (MAMLD1) (CXORF6) on human chromosome Xq28 has been shown to be a causative gene for 46,XY disorders of sex development with hypospadias, the biological function of MAMLD1/Mamld1 remains to be elucidated. In this study, we first showed gradual and steady increase of testicular Mamld1 mRNA expression levels in wild-type male mice from 12.5 to 18.5 d postcoitum. We then generated Mamld1 knockout (KO) male mice and revealed mildly but significantly reduced testicular mRNA levels (65-80%) of genes exclusively expressed in Leydig cells (Star, Cyp11a1, Cyp17a1, Hsd3b1, and Insl3) as well as grossly normal testicular mRNA levels of genes expressed in other cell types or in Leydig and other cell types. However, no demonstrable abnormality was identified for cytochrome P450 17A1 and 3β-hydroxysteroid dehydrogenase (HSD3B) protein expression levels, appearance of external and internal genitalia, anogenital distance, testis weight, Leydig cell number, intratesticular testosterone and other steroid metabolite concentrations, histological findings, in situ hybridization findings for sonic hedgehog (the key molecule for genital tubercle development), and immunohistochemical findings for anti-Müllerian hormone (Sertoli cell marker), HSD3B (Leydig cell marker), and DEAD (Asp-Glu-Ala-Asp) box polypeptide 4 (germ cell marker) in the KO male mice. Fertility was also normal. These findings imply that Mamld1 deficiency significantly reduces mRNA expression levels of multiple genes expressed in mouse fetal Leydig cells but permits normal genital and reproductive development. The contrastive phenotypic findings between Mamld1 KO male mice and MAMLD1 mutation positive patients would primarily be ascribed to species difference in the fetal sex development.

Men and women become infertile with age, but the mechanism of declining male fertility, more specifically, the decrease in in sperm quality, is not well known. Citrate synthase (CS) is a core enzyme of the mitochondrial tricarboxylic acid (TCA) cycle, which directly controls cellular function. Extra-mitochondrial CS (eCS) is produced and abundant in the sperm head; however, its role in male fertility is unknown. We investigated the role of eCS in male fertility by producing eCs-deficient (eCs-KO) mice. The initiation of the first spike of Ca 2+ oscillation was substantially delayed in egg fused with eCs-KO sperm, despite normal expression of sperm factor phospholipase C zeta 1. The eCs-KO male mice were initially fertile, but the fertility dropped with age. Metabolomic analysis of aged sperm revealed that the loss of eCS enhances TCA cycle in the mitochondria with age, presumably leading to depletion of extra-mitochondrial citrate. The data suggest that eCS suppresses age-dependent male infertility, providing insights into the decline of male fertility with age.

Azoospermia affects up to 1% of adult men. Non-obstructive azoospermia is a multifactorial disorder whose molecular basis remains largely unknown. To date, mutations in several genes and multiple submicroscopic copy-number variations (CNVs) have been identified in patients with non-obstructive azoospermia. The aim of this study was to clarify the contribution of nucleotide substitutions in known causative genes and submicroscopic CNVs in the genome to the development of non-obstructive azoospermia. To this end, we conducted sequence analysis of 25 known disease-associated genes using next-generation sequencing and genome-wide copy-number analysis using array-based comparative genomic hybridization. We studied 40 Japanese patients with idiopathic non-obstructive azoospermia. Functional significance of molecular alterations was assessed by in silico analyses. As a result, we identified four putative pathogenic mutations, four rare polymorphisms possibly associated with disease risk, and four probable neutral variants in 10 patients. These sequence alterations included a heterozygous splice site mutation in SOHLH1 and a hemizygous missense substitution in TEX11, which have been reported as causes of non-obstructive azoospermia. Copy-number analysis detected five X chromosomal or autosomal CNVs of unknown clinical significance, in addition to one known pathogenic Y chromosomal microduplication. Five patients carried multiple molecular alterations. The results indicate that monogenic and oligogenic mutations, including those in SOHLH1 and TEX11, account for more than 10% of cases of idiopathic non-obstructive azoospermia. Furthermore, this study suggests possible contributions of substitutions in various genes as well as submicroscopic CNVs on the X chromosome and autosomes to non-obstructive azoospermia, which require further validation.