Variations of C14ORF39 and SYCE1 Identified in Idiopathic Premature Ovarian Insufficiency and Nonobstructive Azoospermia

Defects in mRNA splicing and implications for infertility: a comprehensive review and in silico analysis

BACKGROUND

mRNA splicing is a fundamental process in the reproductive system, playing a pivotal role in reproductive development and endocrine function, and ensuring the proper execution of meiosis, mitosis, and gamete function. Trans-acting factors and cis-acting elements are key players in mRNA splicing whose dysfunction can potentially lead to male and female infertility. Although hundreds of trans-acting factors have been implicated in mRNA splicing, the mechanisms by which these factors influence reproductive processes are fully understood for only a subset. Furthermore, the clinical impact of variations in cis-acting elements on human infertility has not been comprehensively characterized, leading to probable omissions of pathogenic variants in standard genetic analyses.

OBJECTIVE AND RATIONALE

This review aimed to summarize our current understanding of the factors involved in mRNA splicing regulation and their association with infertility disorders. We introduced methods for prioritizing and functionally validating splicing variants associated with human infertility. Additionally, we explored corresponding abnormal splicing therapies that could potentially provide insight into treating human infertility.

SEARCH METHODS

Systematic literature searches of human and model organisms were performed in the PubMed database between May 1977 and July 2024. To identify mRNA splicing-related genes and pathogenic variants in infertility, the search terms 'splice', 'splicing', 'variant', and 'mutation' were combined with azoospermia, oligozoospermia, asthenozoospermia, multiple morphological abnormalities of the sperm flagella, acephalic spermatozoa, disorders of sex development, early embryonic arrest, reproductive endocrine disorders, oocyte maturation arrest, premature ovarian failure, primary ovarian insufficiency, zona pellucida, fertilization defects, infertile, fertile, infertility, fertility, reproduction, and reproductive.

OUTCOMES

Our search identified 5014 publications, of which 291 were included in the final analysis. This review provided a comprehensive overview of the biological mechanisms of mRNA splicing, with a focus on the roles of trans-acting factors and cis-acting elements. We highlighted the disruption of 52 trans-acting proteins involved in spliceosome assembly and catalytic activity and recognized splicing regulatory regions and epigenetic regulation associated with infertility. The 73 functionally validated splicing variants in the cis-acting elements of 54 genes have been reported in 20 types of human infertility; 27 of them were located outside the canonical splice sites and potentially overlooked in standard genetic analysis due to likely benign or of uncertain significance. The in silico prediction of splicing can prioritize potential splicing abnormalities that may be true pathogenic mechanisms. We also summarize the methods for prioritizing splicing variants and strategies for functional validation and review splicing therapy approaches for other diseases, providing a reference for abnormal reproduction treatment.

WIDER IMPLICATIONS

Our comprehensive review of trans-acting factors and cis-acting elements in mRNA splicing will further promote a more thorough understanding of reproductive regulatory processes, leading to improved pathogenic variant identification and potential treatments for human infertility.

REGISTRATION NUMBER

N/A.

Common variation in meiosis genes shapes human recombination phenotypes and aneuploidy risk

The leading cause of human pregnancy loss is aneuploidy, often tracing to errors in chromosome segregation during female meiosis. While abnormal crossover recombination is known to confer risk for aneuploidy, limited data have hindered understanding of the potential shared genetic basis of these key molecular phenotypes. To address this gap, we performed retrospective analysis of preimplantation genetic testing data from 139,416 in vitro fertilized embryos from 22,850 sets of biological parents. By tracing transmission of haplotypes, we identified 3,656,198 crossovers, as well as 92,485 aneuploid chromosomes. Counts of crossovers were lower in aneuploid versus euploid embryos, consistent with their role in chromosome pairing and segregation. Our analyses further revealed that a common haplotype spanning the meiotic cohesin SMC1B is significantly associated with both crossover count and maternal meiotic aneuploidy, with evidence supporting a non-coding cis-regulatory mechanism. Transcriptome- and phenome-wide association tests also implicated variation in the synaptonemal complex component C14orf39 and crossover-regulating ubiquitin ligases CCNB1IP1 and RNF212 in meiotic aneuploidy risk. More broadly, recombination and aneuploidy possess a partially shared genetic basis that also overlaps with reproductive aging traits. Our findings highlight the dual role of recombination in generating genetic diversity, while ensuring meiotic fidelity.

Azoospermia/Oligozoospermia and Prostate Cancer Are Increased in Families of Women With Primary Ovarian Insufficiency

Background

Nonobstructive azoospermia (NOA) and primary ovarian insufficiency (POI) have common genetics that may also predispose patients to cancer risk.

Objectives

We hypothesized that NOA or severe oligozoospermia and the risk of male cancers would be higher in families of women with POI.

Methods

Women with POI were identified using International Classification of Disease codes in electronic medical records (1995-2021) from 2 major healthcare systems in Utah and reviewed for accuracy. Using genealogy information in the Utah Population Database, women with POI (n = 392) and their relatives were included if there were at least 3 generations of ancestors available. Men with NOA or severe oligozoospermia (≤5 million/mL) from the Subfertility Health and Assisted Reproduction and the Environment Study were identified in these families and risk was calculated in relatives compared to population rates. The relative risk of prostate and testicular cancer was examined using the Utah Cancer Registry.

Results

There was an increased risk of NOA/severe oligozoospermia in relatives of women with POI among first- (relative risk 2.8 [95% confidence interval 1.1, 6.7]; P = .03), second- (3.1 [1.1, 6.7]; P = .02), and third-degree relatives (1.8 [1.1, 3.1]; P = .03). In these families with POI and NOA/oligozoospermia (n = 21), prostate cancer risk was higher in first- (3.5 [1.1, 8.1]; P = .016) and second-degree relatives (3.1 [1.9, 4.8]; P = .000008).

Conclusion

The data demonstrate excess familial clustering of severe spermatogenic impairment compared to matched population rates, along with higher prostate cancer risk in relatives of women with POI. These findings support a common genetic contribution to POI, spermatogenic impairment, and prostate cancer.

Mouse modeling of familial human SYCE1 c.197-2A>G splice site mutation leads to meiotic recombination failure and non-obstructive azoospermia

Infertility affects a considerable number of couples at reproductive age, with an incidence of 10-15%. Approximately 25% of cases are classified as idiopathic infertility. Often, errors during the meiotic stage appear to be related to idiopathic infertility. A crucial component during the first meiotic prophase is the synaptonemal complex (SC), which plays a fundamental role in homologous chromosome pairing and meiotic recombination. In many studies with infertile patients, mutations affecting SC-coding genes have been identified. The generation of humanized models has high physiological relevance, helping to clarify the molecular bases of pathology, which in turn is essential for the development of therapeutic procedures. Here, we report the generation and characterization of genetically modified mice carrying a mutation equivalent to SYCE1 c.197-2A>G, previously found in male infertile patients, aiming to determine the actual effects of this mutation on reproductive capacity and to study the underlying molecular mechanisms. Homozygous mutants were infertile. SYCE1 protein was not detected and Syce1 transcript presented minimal levels, suggesting transcript degradation underlying the infertility mechanism. Additionally, homozygous mutants showed impaired homologous chromosome synapsis, meiotic arrest before the pachytene stage, and increased apoptosis of meiotic cells. This study validates the variant as pathogenic and causative of infertility, since the observed dramatic phenotype was attributable to this single homozygous point mutation, when compared to WT and heterozygous littermates. Moreover, although this homozygous point mutation has been only found in infertile men thus far, we anticipate that if it were present in women, it would cause infertility as well, as homozygous female mice also exhibited an infertility phenotype.

BCAS2 and hnRNPH1 orchestrate alternative splicing for DNA double-strand break repair and synapsis in meiotic prophase I

Understanding the intricacies of homologous recombination during meiosis is crucial for reproductive biology. However, the role of alternative splicing (AS) in DNA double-strand breaks (DSBs) repair and synapsis remains elusive. In this study, we investigated the impact of conditional knockout (cKO) of the splicing factor gene Bcas2 in mouse germ cells, revealing impaired DSBs repair and synapsis, resulting in non-obstructive azoospermia (NOA). Employing crosslinking immunoprecipitation and sequencing (CLIP-seq), we globally mapped BCAS2 binding sites in the testis, uncovering its predominant association with 5' splice sites (5'SS) of introns and a preference for GA-rich regions. Notably, BCAS2 exhibited direct binding and regulatory influence on Trp53bp1 (codes for 53BP1) and Six6os1 through AS, unveiling novel insights into DSBs repair and synapsis during meiotic prophase I. Furthermore, the interaction between BCAS2, hnRNPH1, and SRSF3 was discovered to orchestrate Trp53bp1 expression via AS, underscoring its role in meiotic prophase I DSBs repair. In summary, our findings delineate the indispensable role of BCAS2-mediated post-transcriptional regulation in DSBs repair and synapsis during male meiosis. This study provides a comprehensive framework for unraveling the molecular mechanisms governing the post-transcriptional network in male meiosis, contributing to the broader understanding of reproductive biology.

Insights into left-right asymmetric development of chicken ovary at the single-cell level

Avian ovaries develop asymmetrically apart from prey birds, with only the left ovary growing more towards functional organ. Here, we analyze over 135,000 cells from chick's left and right ovaries at six distinct embryonic developmental stages utilizing single-cell transcriptome sequencing. We delineate gene expression patterns across 15 cell types within these embryo ovaries, revealing side-specific development. The left ovaries exhibit cortex cells, zygotene germ cells, and transcriptional changes unique to the left side. Differential gene expression analysis further identifies specific markers and pathways active in these cell types, highlighting the asymmetry in ovarian development. A fine-scale analysis of the germ cell meiotic transcriptome reveals seven distinct clusters with gene expression patterns specific to various meiotic stages. The study also identifies signaling pathways and intercellular communications, particularly between pre-granulosa and germ cells. Spatial transcriptome analysis shows the asymmetry, demonstrating cortex cells exclusively in the left ovary, modulating neighboring cell types through putative secreted signaling molecules. Overall, this single-cell analysis provides insights into the molecular mechanisms of the asymmetric development of avian ovaries, particularly the significant role of cortex cells in the left ovary.

Primary ovarian insufficiency: update on clinical and genetic findings

Primary ovarian insufficiency (POI) is a disorder of insufficient ovarian follicle function before the age of 40 years with an estimated prevalence of 3.7% worldwide. Its relevance is emerging due to the increasing number of women desiring conception late or beyond the third decade of their lives. POI clinical presentation is extremely heterogeneous with a possible exordium as primary amenorrhea due to ovarian dysgenesis or with a secondary amenorrhea due to different congenital or acquired abnormalities. POI significantly impacts non only on the fertility prospect of the affected women but also on their general, psychological, sexual quality of life, and, furthermore, on their long-term bone, cardiovascular, and cognitive health. In several cases the underlying cause of POI remains unknown and, thus, these forms are still classified as idiopathic. However, we now know the age of menopause is an inheritable trait and POI has a strong genetic background. This is confirmed by the existence of several candidate genes, experimental and natural models. The most common genetic contributors to POI are the X chromosome-linked defects. Moreover, the variable expressivity of POI defect suggests it can be considered as a multifactorial or oligogenic defect. Here, we present an updated review on clinical findings and on the principal X-linked and autosomal genes involved in syndromic and non-syndromic forms of POI. We also provide current information on the management of the premature hypoestrogenic state as well as on fertility preservation in subjects at risk of POI.

LH promotes the proliferation of porcine primordial germ cell-like cells (pPGCLCs) by regulating the ceRNA network related to the TGF-β signaling pathway

Primordial germ cells (PGCs), as the precursors of gametes found in early embryos, provide a new direction for solving the problem of reproductive disorders. In vitro, conversion of adult stem cells (ASCs) into primordial germ cell-like cells (PGCLCs) is feasible. The means of increasing PGCLCs number in vitro has been a focus of recent stem cell research. In this study, we found that luteinizing hormone (LH) could promote porcine PGCLCs (pPGCLCs) proliferation. To investigate the proliferation regulatory network, whole transcriptome sequencing technology was employed. Results showed that the TGF-β signaling pathway played a key role. In addition, we found that TGFβR1 and SMAD4, TGF-β signaling pathway-related genes, were significantly upregulated after LH treatment. Subsequently, we predicted their target microRNAs (miRNAs) and long non-coding RNAs (lncRNAs): ssc-miR-128, ssc-miR-146b, ssc-miR-361-3p, MSTRG.11473, MSTRG.11475, MSTRG.11553, and MSTRG.11554, and constructed the competitive endogenous RNAs (ceRNA) network. Finally, to further verify the ceRNA network, the miRNA-inhibitors were transfected into cells. RT-qPCR results indicated a significant increase in the expression of MSTRG.11473, MSTRG.11475, MSTRG.11553, MSTRG.11554, TGFβR1, and SMAD4 compared to the negative control (NC) group. In conclusion, these results highlight that LH could regulate the pPGCLCs proliferation by modulating the expression of TGF-β signaling pathway-related ncRNAs.

How exome sequencing improves the diagnostics and management of men with non-syndromic infertility

Male infertility affects approximately 17% of all men and represents a complex disorder in which not only semen parameters such as sperm motility, morphology, and number of sperm are highly variable, but also testicular phenotypes range from normal spermatogenesis to complete absence of germ cells. Genetic factors significantly contribute to the disease but chromosomal aberrations, mostly Klinefelter syndrome, and microdeletions of the Y-chromosome have remained the only diagnostically and clinically considered genetic causes. Monogenic causes remain understudied and, thus, often unidentified, leaving the majority of the male factor couple infertility pathomechanistically unexplained. This has been changing mostly because of the introduction of exome sequencing that allows the analysis of multiple genes in large patient cohorts. As a result, pathogenic variants in single genes have been associated with non-syndromic forms of all aetiologic sub-categories in the last decade. This review highlights the contribution of exome sequencing to the identification of novel disease genes for isolated (non-syndromic) male infertility by presenting the results of a comprehensive literature search. Both, reduced sperm count in azoospermic and oligozoospermic patients, and impaired sperm motility and/or morphology, in asthenozoospermic and/or teratozoospermic patients are highly heterogeneous diseases with well over 100 different candidate genes described for each entity. Applying the standardized evaluation criteria of the ClinGen gene curation working group, 70 genes with at least moderate evidence to contribute to the disease are highlighted. The implementation of these valid disease genes in clinical exome sequencing is important to increase the diagnostic yield in male infertility and, thus, improve clinical decision-making and appropriate genetic counseling. Future advances in androgenetics will continue to depend on large-scale exome and genome sequencing studies of comprehensive international patient cohorts, which are the most promising approaches to identify additional disease genes and provide reliable data on the gene-disease relationship.

Homozygous missense variant in MEIOSIN causes premature ovarian insufficiency

STUDY QUESTION

Are variants of genes involved in meiosis initiation responsible for premature ovarian insufficiency (POI)?

SUMMARY ANSWER

A MEIOSIN variant participates in the pathogenesis of human POI by impairing meiosis due to insufficient transcriptional activation of essential meiotic genes.

WHAT IS KNOWN ALREADY

Meiosis is the key event for the establishment of the ovarian reserve, and several gene defects impairing meiotic homologous recombination have been found to contribute to the pathogenesis of POI. Although STRA8 and MEIOISN variants have been found to associate with POI in a recent study, the condition of other meiosis initiation genes is unknown and direct evidence of variants participating in the pathogenesis of POI is still lacking.

STUDY DESIGN, SIZE, DURATION

This was a retrospective genetic study. An in-house whole exome sequencing (WES) database of 1030 idiopathic POI patients was screened for variations of meiosis initiation genes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Homozygous or compound heterozygous variations of genes involved in meiosis initiation were screened in the in-house WES database. The pathogenicity of the variation was verified by in vitro experiments, including protein structure prediction and dual-luciferase reporter assay. The effect of the variant on ovarian function and meiosis was demonstrated through histological analyses in a point mutation mouse model.

MAIN RESULTS AND THE ROLE OF CHANCE

One homozygous variant in MEIOSIN (c.1735C>T, p.R579W) and one in STRA8 (c.258 + 1G>A), which initiates meiosis via the retinoic acid-dependent pathway, were identified in a patient with idiopathic POI respectively. The STRA8 variation has been reported in the recently published work. For the MEIOSIN variation, the dual-luciferase reporter assay revealed that the variant adversely affected the transcriptional function of MEIOSIN in upregulating meiotic genes. Furthermore, knock-in mice with the homologous mutation confirmed that the variation impacted the meiotic prophase I program and accelerated oocyte depletion. Moreover, the variant p.R579W localizing in the high-mobility group (HMG) box domain disrupted the nuclear localization of the MEIOSIN protein but was dispensable for the cell-cycle switch of oocytes, suggesting a unique role of the MEIOSIN HMG box domain in meiosis initiation.

LIMITATIONS, REASONS FOR CAUTION

Further studies are needed to explore the role of other meiosis initiation genes in the pathogenesis of POI.

WIDER IMPLICATIONS OF THE FINDINGS

The MEIOSIN variant was verified to cause POI by impaired transcriptional regulation of meiotic genes and was inherited by a recessive mode. The function of HMG box domain in MEIOSIN protein was also expanded by this study. Although causative variations in meiotic initiation genes are rare in POI, our study confirmed the pathogenicity of a MEIOSIN variant and elucidated another mechanism of human infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Key Research & Developmental Program of China (2022YFC2703800, 2022YFC2703000), National Natural Science Foundation for Distinguished Young Scholars (82125014), National Natural Science Foundation of China (32070847, 32170867, 82071609), Basic Science Center Program of NSFC (31988101), Natural Science Foundation of Shandong Province for Grand Basic Projects (ZR2021ZD33), Natural Science Foundation of Shandong Province for Excellent Young Scholars (ZR2022YQ69), Taishan Scholars Program for Young Experts of Shandong Province (tsqn202211371), and Qilu Young Scholars Program of Shandong University. The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Meiotic Chromosome Structure, the Synaptonemal Complex, and Infertility

In meiosis, homologous chromosome synapsis is mediated by a supramolecular protein structure, the synaptonemal complex (SC), that assembles between homologous chromosome axes. The mammalian SC comprises at least eight largely coiled-coil proteins that interact and self-assemble to generate a long, zipper-like structure that holds homologous chromosomes in close proximity and promotes the formation of genetic crossovers and accurate meiotic chromosome segregation. In recent years, numerous mutations in human SC genes have been associated with different types of male and female infertility. Here, we integrate structural information on the human SC with mouse and human genetics to describe the molecular mechanisms by which SC mutations can result in human infertility. We outline certain themes in which different SC proteins are susceptible to different types of disease mutation and how genetic variants with seemingly minor effects on SC proteins may act as dominant-negative mutations in which the heterozygous state is pathogenic.

DNA double-strand break genetic variants in patients with premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a clinically heterogeneous disease that may seriously affect the physical and mental health of women of reproductive age. POI primarily manifests as ovarian function decline and endocrine disorders in women prior to age 40 and is an established cause of female infertility. It is crucial to elucidate the causative factors of POI, not only to expand the understanding of ovarian physiology, but also to provide genetic counselling and fertility guidance to affected patients. Factors leading to POI are multifaceted with genetic factors accounting for 7% to 30%. In recent years, an increasing number of DNA damage-repair-related genes have been linked with the occurrence of POI. Among them, DNA double-strand breaks (DSBs), one of the most damaging to DNA, and its main repair methods including homologous recombination (HR) and non-homologous end joining (NHEJ) are of particular interest. Numerous genes are known to be involved in the regulation of programmed DSB formation and damage repair. The abnormal expression of several genes have been shown to trigger defects in the overall repair pathway and induce POI and other diseases. This review summarises the DSB-related genes that may contribute to the development of POI and their potential regulatory mechanisms, which will help to further establish role of DSB in the pathogenesis of POI and provide theoretical guidance for the study of the pathogenesis and clinical treatment of this disease.

Genetic variants underlying spermatogenic arrests in men with non-obstructive azoospermia

Spermatogenic arrest is a severe form of non-obstructive azoospermia (NOA), which occurs in 10-15% of infertile men. Interruption in spermatogenic progression at premeiotic, meiotic, or postmeiotic stage can lead to arrest in men with NOA. Recent studies have intensively focused on defining genetic variants underlying these spermatogenic arrests by making genome/exome sequencing. A number of variants were discovered in the genes involving in mitosis, meiosis, germline differentiation and other basic cellular events. Herein, defined variants in NOA cases with spermatogenic arrests and created knockout mouse models for the related genes are comprehensively reviewed. Also, importance of gene panel-based screening for NOA cases was discussed. Screening common variants in these infertile men with spermatogenic arrests may contribute to elucidating the molecular background and designing novel treatment strategies.

Mechanisms of ovarian aging in women: a review

Ovarian aging is a natural and physiological aging process characterized by loss of quantity and quality of oocyte or follicular pool. As it is generally accepted that women are born with a finite follicle pool that will go through constant decline without renewing, which, together with decreased oocyte quality, makes a severe situation for women who is of advanced age but desperate for a healthy baby. The aim of our review was to investigate mechanisms leading to ovarian aging by discussing both extra- and intra- ovarian factors and to identify genetic characteristics of ovarian aging. The mechanisms were identified as both extra-ovarian alternation of hypothalamic-pituitary-ovarian axis and intra-ovarian alternation of ovary itself, including telomere, mitochondria, oxidative stress, DNA damage, protein homeostasis, aneuploidy, apoptosis and autophagy. Moreover, here we reviewed related Genome-wide association studies (GWAS studies) from 2009 to 2021 and next generation sequencing (NGS) studies of primary ovarian insufficiency (POI) in order to describe genetic characteristics of ovarian aging. It is reasonable to wish more reliable anti-aging interventions for ovarian aging as the exploration of mechanisms and genetics being progressing.

Genetic screening in patients with ovarian dysfunction

Ovarian dysfunction, including premature ovarian insufficiency and decreased ovarian reserve, affects the ovarian reserve and is one of the leading causes of female infertility. More and more cases of ovarian dysfunction are associated with genetic factors. Here, we identified eight potential variants in five genes (MSH4, HFM1, SYCE1, FSHR, and C14orf39) from six independent families by exome sequencing. The splice-site variants in SYCE1 and MSH4 affected canonical splicing isoforms, leading to missing protein domains or premature termination. Our findings expand the mutational spectrum of ovarian dysfunction and provide potential biomarkers for future genetic counseling and for more personalized treatments. Exome sequencing was shown to be a useful tool to better dissect the genetic basis for ovarian dysfunction and yielded a genetic diagnosis in about 5.0% (6/124) of cases in a cohort of 124 patients with ovarian dysfunction.

Transcriptomic differences between fibrotic and non-fibrotic testicular tissue reveal possible key players in Klinefelter syndrome-related testicular fibrosis

Klinefelter syndrome (KS; 47,XXY) affects 1-2 in 1000 males. Most men with KS suffer from an early germ cell loss and testicular fibrosis from puberty onwards. Mechanisms responsible for these processes remain unknown. Previous genomics studies on testis tissue from men with KS focused on germ cell loss, while a transcriptomic analysis focused on testicular fibrosis has not yet been performed. This study aimed to identify factors involved in the fibrotic remodelling of KS testes by analysing the transcriptome of fibrotic and non-fibrotic testicular tissue. RNA sequencing was performed to compare the genes expressed in testicular samples with (KS and testis atrophy) and without (Sertoli cell-only syndrome and fertile controls) fibrosis (n = 5, each). Additionally, differentially expressed genes (DEGs) between KS and testis atrophy samples were studied to reveal KS-specific fibrotic genes. DEGs were considered significant when p < 0.01 and log2FC > 2. Next, downstream analyses (GO and KEGG) were performed. Lastly, RNA in situ hybridization was performed to validate the results. The first analysis (fibrotic vs non-fibrotic) resulted in 734 significant DEGs (167 up- and 567 down-regulated). Genes involved in the extracellular structure organization (e.g. VCAM1) were found up-regulated. KEGG analysis showed an up-regulation of genes involved in the TGF-β pathway. The KS vs testis atrophy analysis resulted in 539 significant DEGs (59 up- and 480 down-regulated). Chronic inflammatory response genes were found up-regulated. The overlap of X-linked DEGs from the two analyses revealed three genes: matrix-remodelling associated 5 (MXRA5), doublecortin (DCX) and variable charge X-Linked 3B (VCX3B). RNA in situ hybridization showed an overexpression of VCAM1, MXRA5 and DCX within the fibrotic group compared with the non-fibrotic group. To summarize, this study revealed DEGs between fibrotic and non-fibrotic testis tissue, including VCAM1. In addition, X-linked fibrotic genes were revealed, e.g. MXRA5, DCX and VCX3B. Their potential role in KS-related testicular fibrosis needs further study.

Pathogenic variants in TSC2 might cause premature ovarian insufficiency through activated mTOR induced hyperactivation of primordial follicles

OBJECTIVE

To investigate the role of tuberous sclerosis complex (TSC) genes, including TSC1 and TSC2, in the pathogenesis of human premature ovarian insufficiency (POI).

DESIGN

Genetic and functional study.

SETTING

University-based reproductive medical center.

PATIENT(S)

Six patients from a cohort of 1,030 cases with idiopathic POI.

INTERVENTION(S)

Variants in TSC1 and TSC2 were screened through the largest in-house database of whole exome sequencing performed in 1,030 patients with idiopathic POI. The pathogenic effects of the variants were further verified by functional studies.

MAIN OUTCOME MEASURE(S)

TSC1 or TSC2 variant and functional characteristics.

RESULT(S)

Five pathogenic heterozygous variants in TSC2 were identified in 6 patients with POI. Functional studies showed these variants impaired the repressive effect of TSC2 on mammalian target of rapamycin (mTOR) pathway by disrupting the formation of TSC complex or its GTPase-activating protein activity. Furthermore, in vitro ovarian culture assay showed that TSC2 p.R98Q led to hyperactivation of mTOR pathway thereby triggering primordial follicle activation.

CONCLUSION(S)

The present study identified pathogenic variants of TSC2 in patients with POI, firstly suggested defective TSC/mTOR pathway mediated hyperactivation of primordial follicle participating in the pathogenesis of POI, giving insights into new targets of genetic counseling and clinical prevention for POI. Considering the pivotal role of TSC2 variants in diagnosis of TSC syndrome, the present study also highlighted the importance of history collection and long-term follow-up for the TSC2 variants carriers.

Fetal germ cell development in humans, a link with infertility

Gametes are cells that have the unique ability to give rise to new individuals as well as transmit (epi)genetic information across generations. Generation of functionally competent gametes, oocytes and sperm cells, depends to some extent on several fundamental processes that occur during fetal development. Direct studies on human fetal germ cells remain hindered by ethical considerations and inaccessibility to human fetal material. Therefore, the majority of our current knowledge of germ cell development still comes from an invaluable body of research performed using different mammalian species. During the last decade, our understanding of human fetal germ cells has increased due to the successful use of human pluripotent stem cells to model aspects of human early gametogenesis and advancements on single-cell omics. Together, this has contributed to determine the cell types and associated molecular signatures in the developing human gonads. In this review, we will put in perspective the knowledge obtained from several mammalian models (mouse, monkey, pig). Moreover, we will discuss the main events during human fetal (female) early gametogenesis and how the dysregulation of this highly complex and lengthy process can link to infertility later in life.

Identification of sex determination locus in sea cucumber Apostichopus japonicus using genome-wide association study

Background

Sex determination mechanisms are complicated and diverse across taxonomic categories. Sea cucumber Apostichopus japonicus is a benthic echinoderm, which is the closest group of invertebrates to chordate, and important economic and ecologically aquaculture species in China. A. japonicus is dioecious, and no phenotypic differences between males and females can be detected before sexual maturation. Identification of sex determination locus will broaden knowledge about sex-determination mechanism in echinoderms, which allows for the identification of sex-linked markers and increases the efficiency of sea cucumber breeding industry.

Results

Here, we integrated assembly of a novel chromosome-level genome and resequencing of female and male populations to investigate the sex determination mechanisms of A. japonicus. We built a chromosome-level genome assembly AJH1.0 using Hi-C technology. The assembly AJH1.0 consists of 23 chromosomes ranging from 22.4 to 60.4 Mb. To identify the sex-determination locus of A. japonicus, we conducted genome-wide association study (GWAS) and analyses of distribution characteristics of sex-specific SNPs and fixation index F_ST. The GWAS analysis showed that multiple sex-associated loci were located on several chromosomes, including chromosome 4 (24.8%), followed by chromosome 9 (10.7%), chromosome 17 (10.4%), and chromosome 18 (14.1%). Furthermore, analyzing the homozygous and heterozygous genotypes of plenty of sex-specific SNPs in females and males confirmed that A. japonicus might have a XX/XY sex determination system. As a physical region of 10 Mb on chromosome 4 included the highest number of sex-specific SNPs and higher F_ST values, this region was considered as the candidate sex determination region (SDR) in A. japonicus.

Conclusions

In the present study, we integrated genome-wide association study and analyses of sex-specific variations to investigate sex determination mechanisms. This will bring novel insights into gene regulation during primitive gonadogenesis and differentiation and identification of master sex determination gene in sea cucumber. In the sea cucumber industry, investigation of molecular mechanisms of sex determination will be helpful for artificial fertilization and precise breeding.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08632-3.

Homozygous missense mutation in CCDC155 disrupts the transmembrane distribution of CCDC155 and SUN1, resulting in non-obstructive azoospermia and premature ovarian insufficiency in humans

Non-obstructive azoospermia (NOA) and premature ovarian insufficiency (POI) represent the most serious forms of human infertility caused by gametogenic failure. Although whole-exome sequencing (WES) has uncovered multiple monogenic causes of human infertility, our knowledge of the genetic basis of human gametogenesis defects remains at a rudimentary stage. Coiled-coil-domain-containing protein 155 (CCDC155) encodes a core component of the linker of the nucleoskeleton and cytoskeleton complex that is essential for modulating telomere-led chromosome movements during the meiotic prophase of mice. Additionally, Ccdc155 deficiency in mice causes infertility in both sexes with meiotic arrest. In this study, we applied WES to identify the pathogenic genes for 15 NOA and POI patients whose parents were consanguineous and identified a novel homozygous missense mutation in CCDC155 [c.590T>C (p.Leu197Pro)] in a pair of familial NOA and POI patients whose parents were first cousins. The affected spermatocytes were unable to complete meiotic division coupled with unresolved repair of the DNA double-strand break. This rare missense mutation with lesions in the conserved CC domain of CCDC155 blocked nuclear envelope (NE) distribution and subsequently prevented NE-specific enrichment of Sad1- and UNC84-domain-containing 1 either ex vivo or in vitro, eventually leading to disruptive NE anchoring of chromosome-induced meiotic arrest in both sexes. This study presents the first evidence of the necessity of the SUN1-CCDC155 complex during human meiosis and provides insight into the CCDC155 CC domain, thereby expanding the genetic spectrum of human NOA and POI and promoting adequate genetic counselling and appropriate fertility guidance for these patients.

Whole-exome sequencing improves the diagnosis and care of men with non-obstructive azoospermia

Non-obstructive azoospermia (NOA) is a severe and frequent cause of male infertility, often treated by testicular sperm extraction followed by intracytoplasmic sperm injection. The aim of this study is to improve the genetic diagnosis of NOA, by identifying new genes involved in human NOA and to better assess the chances of successful sperm extraction according to the individual's genotype. Exome sequencing was performed on 96 NOA-affected individuals negative for routine genetic tests. Bioinformatics analysis was limited to a panel of 151 genes selected as known causal or candidate genes for NOA. Only highly deleterious homozygous or hemizygous variants were retained as candidates. A likely causal defect was identified in 16 genes in a total of 22 individuals (23%). Six genes had not been described in man (DDX25, HENMT1, MCMDC2, MSH5, REC8, TDRKH) and 10 were previously reported (C14orf39, DMC1, FANCM, GCNA, HFM1, MCM8, MEIOB, PDHA2, TDRD9, TERB1). Seven individuals had defects in genes from piwi or DNA repair pathways, three in genes involved in post-meiotic maturation, and 12 in meiotic processes. Interestingly, all individuals with defects in meiotic genes had an unsuccessful sperm retrieval, indicating that genetic diagnosis prior to TESE could help identify individuals with low or null chances of successful sperm retrieval and thus avoid unsuccessful surgeries.