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STUDY QUESTION Can new genetic factors responsible for male infertility be identified, especially for those characterized by asthenospermia despite normal sperm morphology? SUMMARY ANSWER We identified the novel pathogenetic gene IQ motif and ubiquitin-like domain-containing (IQUB) as responsible for male infertility characterized by asthenospermia, involving sperm radial spoke defects. WHAT IS KNOWN ALREADY To date, only a few genes have been found to be responsible for asthenospermia with normal sperm morphology. Iqub, encoding the IQUB protein, is highly and specifically expressed in murine testes and interacts with the proteins radial spoke head 3 (RSPH3), CEP295 N-terminal like (CEP295NL or DDC8), glutathione S-transferase mu 1 (GSTM1) and outer dense fiber of sperm tails 1 (ODF1) in the yeast two-hybrid system. STUDY DESIGN, SIZE, DURATION The IQUB variant was identified by whole-exome sequencing in a cohort of 126 male infertility patients with typical asthenospermia recruited between 2015 and 2020. Knockout (KO) and knockin (KI) mouse models, scanning and transmission electron microscopy (TEM), and other functional assays were performed, between 2019 and 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS The IQUB variant was identified by whole-exome sequencing and confirmed by Sanger sequencing. Iqub KO and KI mice were constructed to mimic the phenotype of the affected individual. After recapitulating the phenotype of human male infertility, scanning and TEM were performed to check the ultrastructure of the sperm. Western blot and co-immunoprecipitation were performed to clarify the pathological mechanism of the IQUB variant. MAIN RESULTS AND THE ROLE OF CHANCE We identified a homozygous nonsense IQUB variant (NM_001282855.2:c.942T> G(p.Tyr314*)) from an infertile male. Iqub KO and KI mice mimicked the infertility phenotype and confirmed IQUB to be the pathogenetic gene. Scanning and TEM showed that sperm of both the mouse models and the affected individual had radial spoke defects. The functional assay suggested that IQUB may recruit calmodulin in lower Ca2+ environments to facilitate the normal assembly of radial spokes by inhibiting the activity of RSPH3/p-ERK1/2 (a nontypical AKAP (A-Kinase Anchoring Protein) forming by RSPH3 and phosphorylation of extracellular signal-regulated kinase 1 and 2 (p-ERK1/2)). LIMITATIONS, REASONS FOR CAUTION Additional cases are needed to confirm the genetic contribution of IQUB variants to male infertility. In addition, because no IQUB antibody is available for immunofluorescence and the polyclonal antibody we generated was only effective in western blotting, immunostaining for IQUB was not performed in this study. Therefore, this study lacks direct in vivo proof to confirm the effect of the variant on IQUB protein level. WIDER IMPLICATIONS OF THE FINDINGS Our results suggest a causal relation between IQUB variants and male infertility owing to asthenospermia, and partly clarify the pathological mechanism of IQUB variants. This expands our knowledge of the genes involved in human sperm asthenospermia and potentially provides a new genetic marker for male infertility. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Key Research and Development Program of China (2021YFC2700100), the National Natural Science Foundation of China (32130029, 82171643, 81971450, 82001538, and 81971382) and the Guangdong Science and Technology Department Guangdong-Hong Kong-Macao Joint Innovation Project (2020A0505140003). There are no competing interests to declare. TRIAL REGISTRATION NUMBER N/A.

Fertilization is a fundamental process of development, and the blocking mechanisms act at the zona pellucida (ZP) and plasma membrane of the egg to prevent any additional sperm from binding, permeating and fusing after fertilization. In clinical practice, some couples undergoing recurrent IVF failures that mature oocytes had abnormal fertilization for unknown reason. Ovastacin encoded by ASTL cleave the ZP protein ZP2 and play a key role in preventing polyspermy. Here, we identified bi-allelic variants in ASTL that are mainly characterized by fertilization problems in humans. All four independent affected individuals had bi-allelic frameshift variants or predicted damaging missense variants, which follow a Mendelian recessive inheritance pattern. The frameshift variants significantly decreased the quantity of ASTL protein in vitro. And all missense variants affected the enzymatic activity that cleaves ZP2 in mouse egg in vitro. Three knock-in female mice (corresponding to three missense variants in patients) all show subfertility due to low embryo developmental potential. This work presents strong evidence that pathogenic variants in ASTL cause female infertility and provides a new genetic marker for the diagnosis of fertilization problems.

STUDY QUESTION Are mutations in MOS (MOS proto-oncogene, serine/threonine kinase) involved in early embryonic arrest in infertile women? SUMMARY ANSWER We identified mutations in MOS that may cause human female infertility characterized by preimplantation embryonic arrest (PREMBA), and the effects of the mutations in human embryonic kidney 293T (HEK293T cells) and mouse oocytes provided evidence for a causal relation between MOS and female infertility. WHAT IS KNOWN ALREADY MOS, an activator of mitogen-activated protein kinase, mediates germinal vesicle breakdown and metaphase II arrest. Female MOS knockout mice are viable but sterile. Thus, MOS seems to be an important part of the mammalian cell cycle mechanism that regulates female meiosis. STUDY DESIGN, SIZE, DURATION Whole-exome sequencing, bioinformatics filtering analysis and genetic analysis were performed to identify two different biallelic mutations in MOS in two independent families. The infertile patients presenting with early embryonic arrest were recruited from October 2018 to June 2020. PARTICIPANTS/MATERIALS, SETTING, METHODS The female patients diagnosed with primary infertility were recruited from the reproduction centres of local hospitals. Genomic DNA from the affected individuals, their family members and healthy controls was extracted from peripheral blood. We performed whole-exome sequencing in patients diagnosed with PREMBA. Functional effects of the mutations were investigated in HEK293T cells by western blotting and in mouse oocytes by microinjection and immunofluorescence. MAIN RESULTS AND THE ROLE OF CHANCE We identified the homozygous missense mutation c.285C>A (p.(Asn95Lys)) and the compound heterozygous mutations c.467delG (p.(Gly156Alafs*18)) and c.956G>A (p.(Arg319His)) in MOS in two independent patients. The mutations c.285C>A (p.(Asn95Lys)) and c.467delG (p.(Gly156Alafs*18)) reduced the protein level of MOS, and all mutations reduced the ability of MOS to phosphorylate its downstream target, extracellular signal-regulated kinase1/2. In addition, the identified mutations reduced the capacity of exogenous human MOS to rescue the metaphase II exit phenotype, and the F-actin cytoskeleton of mouse oocytes was affected by the patient-derived mutations. LIMITATIONS, REASONS FOR CAUTION Owing to the lack of in vivo data from patient oocytes, the exact molecular mechanism affected by MOS mutations and leading to PREMBA is still unknown and should be further investigated using knock-out or knock-in mice. WIDER IMPLICATIONS OF THE FINDINGS We identified recessive mutations in MOS in two independent patients with the PREMBA phenotype. Our findings reveal the important role of MOS during human oocyte meiosis and embryonic development and suggest that mutations in MOS may be precise diagnostic markers for clinical genetic counselling. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Natural Science Foundation of China (81725006, 81822019, 81771581, 81971450, 81971382,82001538 and 82071642), the project supported by the Shanghai Municipal Science and Technology Major Project (2017SHZDZX01), the Project of the Shanghai Municipal Science and Technology Commission (19JC1411001), the Natural Science Foundation of Shanghai (19ZR1444500 and 21ZR1404800), the Shuguang Program of the Shanghai Education Development Foundation and the Shanghai Municipal Education Commission (18SG03), the Foundation of the Shanghai Health and Family Planning Commission (20154Y0162), the Capacity Building Planning Program for Shanghai Women and Children’s Health Service and the collaborative innovation centre project construction for Shanghai Women and Children’s Health. The authors have no conflicts of interest to declare. TRIAL REGISTRATION NUMBER N/A.

STUDY QUESTION Are any novel mutations and corresponding new phenotypes, other than recurrent hydatidiform moles, seen in patients with MEI1 mutations? SUMMARY ANSWER We identified several novel mutations in MEI1 causing new phenotypes of early embryonic arrest and recurrent implantation failure. WHAT IS KNOWN ALREADY It has been reported that biallelic mutations in MEI1, encoding meiotic double-stranded break formation protein 1, cause azoospermia in men and recurrent hydatidiform moles in women. STUDY DESIGN, SIZE, DURATION We first focused on a pedigree in which two sisters were diagnosed with recurrent hydatidiform moles in December 2018. After genetic analysis, two novel mutations in MEI1 were identified. We then expanded the mutational screening to patients with the phenotype of embryonic arrest, recurrent implantation failure, and recurrent pregnancy loss, and found another three novel MEI1 mutations in seven new patients from six families recruited from December 2018 to May 2020. PARTICIPANTS/MATERIALS, SETTING, METHODS Nine primary infertility patients were recruited from the reproduction centers in local hospitals. Genomic DNA from the affected individuals, their family members, and healthy controls was extracted from peripheral blood. The MEI1 mutations were screened using whole-exome sequencing and were confirmed by the Sanger sequencing. In silico analysis of mutations was performed with Sorting Intolerant From Tolerant (SIFT) and Protein Variation Effect Analyzer (PROVEAN). The influence of the MEI1 mutations was determined by western blotting and minigene analysis in vitro. MAIN RESULTS AND THE ROLE OF CHANCE In this study, we identified five novel mutations in MEI1 in nine patients from seven independent families. Apart from recurrent hydatidiform moles, biallelic mutations in MEI1 were also associated with early embryonic arrest and recurrent implantation failure. In addition, we demonstrated that protein-truncating and missense mutations reduced the protein level of MEI1, while the splicing mutations caused abnormal alternative splicing of MEI1. LIMITATIONS, REASONS FOR CAUTION Owing to the lack of in vivo data from the oocytes of the patients, the exact molecular mechanism(s) involved in the phenotypes remains unknown and should be further investigated using knock-out or knock-in mice. WIDER IMPLICATIONS OF THE FINDINGS Our results not only reveal the important role of MEI1 in human oocyte meiosis and early embryonic development, but also extend the phenotypic and mutational spectrum of MEI1 and provide new diagnostic markers for genetic counseling of clinical patients. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Key Research and Development Program of China (2018YFC1003800, 2017YFC1001500, and 2016YFC1000600), the National Natural Science Foundation of China (81725006, 81822019, 81771581, 81971450, and 81971382), the project supported by the Shanghai Municipal Science and Technology Major Project (2017SHZDZX01), the Project of the Shanghai Municipal Science and Technology Commission (19JC1411001), the Natural Science Foundation of Shanghai (19ZR1444500), the Shuguang Program of the Shanghai Education Development Foundation and the Shanghai Municipal Education Commission (18SG03), the Shanghai Health and Family Planning Commission Foundation (20154Y0162), the Strategic Collaborative Research Program of the Ferring Institute of Reproductive Medicine, Ferring Pharmaceuticals and the Chinese Academy of Sciences (FIRMC200507) and the Chongqing Key Laboratory of Human Embryo Engineering (2020KFKT008). No competing interests are declared. TRIAL REGISTRATION NUMBER N/A.

STUDY QUESTION Can any new genetic factors responsible for early embryonic arrest in infertile patients be identified, together with the mechanism of pathogenic variants? SUMMARY ANSWER We identified three homozygous variants in the F-box protein 43 gene (FBXO43) in infertile patients and studies on the effects of the variants in HEK293T cells and mouse oocytes provided evidence for a causal relation between FBXO43 and female infertility. WHAT IS KNOWN ALREADY FBXO43, an inhibitor of the anaphase-promoting complex/cyclosome, mediates Metaphase II arrest as a component of the cytostatic factor in oocytes. Both male and female Fbxo43 knockout mice are viable but sterile. FBXO43, therefore, appears to be an essential component of the mammalian cell-cycle machinery that regulates both male and female meiosis. Until now, only one article has reported a homozygous FBXO43 variant associated with teratozoospermia, but the causal relationship was not established with functional evidence. STUDY DESIGN, SIZE, DURATION Whole-exome sequencing (WES) and homozygosity mapping were performed in 24 probands from consanguineous families who suffered from early embryonic arrest, and two different homozygous variants in FBXO43 were identified in two independent families. WES data from a further 950 infertile women with early embryonic arrest were screened for homozygous and compound heterozygous variants in FBXO43, and a third individual with an additional homozygous variant in FBXO43 was identified. The infertile patients presenting with early embryonic arrest were recruited from August 2016 to May 2020. PARTICIPANTS/MATERIALS, SETTING, METHODS The women diagnosed with primary infertility were recruited from the reproduction centers of local hospitals. Genomic DNA samples from the affected individuals, their family members, and healthy controls were extracted from peripheral blood. The FBXO43 variants were identified using WES, homozygosity mapping, in silico analysis, and variant screening. All of the variants were confirmed by Sanger sequencing, and the effects of the variants were investigated in human embryonic kidney (HEK) 293T cells by western blotting and in mouse oocytes by complementary RNA injection. MAIN RESULTS AND THE ROLE OF CHANCE We identified three homozygous variants in FBXO43 (NM_001029860.4)—namely, c.1490_1497dup (p.(Glu500Serfs*2)), c.1747C>T (p.(Gln583*)), and c.154delG (p.(Asp52Thrfs*30))—in three independent families. All of the homozygous variants reduced the protein level of FBXO43 and reduced the level of its downstream target Cyclin B1 in HEK293T cells. In addition, the variants reduced the ability of exogenous human FBXO43 to rescue the parthenogenetic activation phenotype in Fbxo43 knockdown mouse oocytes. LIMITATIONS, REASONS FOR CAUTION Owing to the lack of in vivo data from the oocytes of patients, the exact molecular mechanism remains unknown and should be further investigated using knock out or knock in mice. WIDER IMPLICATIONS OF THE FINDINGS Our study has identified three pathogenic variants in FBXO43 that are involved in human early embryonic arrest. These findings contribute to our understanding of the role of FBXO43 in human early embryonic development and provide a new genetic marker for female infertility. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the National Key Research and Development Program of China (2018YFC1003800, 2017YFC1001500, and 2016YFC1000600), the National Natural Science Foundation of China (81725006, 81822019, 81771581, 81971450, 81971382, and 82001552), the project supported by the Shanghai Municipal Science and Technology Major Project (2017SHZDZX01), the Project of the Shanghai Municipal Science and Technology Commission (19JC1411001), the Natural Science Foundation of Shanghai (19ZR1444500), the Shuguang Program of the Shanghai Education Development Foundation and the Shanghai Municipal Education Commission (18SG03), the Foundation of the Shanghai Health and Family Planning Commission (20154Y0162), the Capacity Building Planning Program for Shanghai Women and Children’s Health Service, and the collaborative innovation center project construction for Shanghai Women and Children’s Health. None of the authors have any competing interests. TRIAL REGISTRATION NUMBER N/A