A nonsense mutation in Ccdc62 gene is responsible for spermiogenesis defects and male infertility in repro29/repro29 mice

A novel missense mutation of CCDC34 causes male infertility with oligoasthenoteratozoospermia in a consanguineous Pakistani family

ABSTRACT

Male infertility is a worldwide health issue, affecting 8%-12% of the global population. Oligoasthenoteratozoospermia (OAT) represents a severe type of male infertility, characterized by reduced sperm count and motility and an increased frequency of sperm with aberrant morphology. Using whole-exome sequencing, this study identified a novel missense mutation (c.848C>A, p.A283E) in the coiled-coil domain-containing 34 gene (CCDC34) in a consanguineous Pakistani family. This rare mutation was predicted to be deleterious and to affect the protein stability. Hematoxylin and eosin staining of spermatozoa from the patient with OAT revealed multiple morphological abnormalities of the flagella and transmission electron microscopy indicated axonemal ultrastructural defects with a lack of outer dynein arms. These findings indicated that CCDC34 plays a role in maintaining the axonemal ultrastructure and the assembly or stability of the outer dynein arms, thus expanding the phenotypic spectrum of CCDC34 missense mutations.

CCDC157 is essential for sperm differentiation and shows oligoasthenoteratozoospermia-related mutations in men

Oligoasthenoteratospermia (OAT), characterized by abnormally low sperm count, poor sperm motility, and abnormally high number of deformed spermatozoa, is an important cause of male infertility. Its genetic basis in many affected individuals remains unknown. Here, we found that CCDC157 variants are associated with OAT. In two cohorts, a 21-bp (g.30768132_30768152del21) and/or 24-bp (g.30772543_30772566del24) deletion of CCDC157 were identified in five sporadic OAT patients, and 2 cases within one pedigree. In a mouse model, loss of Ccdc157 led to male sterility with OAT-like phenotypes. Electron microscopy revealed misstructured acrosome and abnormal head-tail coupling apparatus in the sperm of Ccdc157-null mice. Comparative transcriptome analysis showed that the Ccdc157 mutation alters the expressions of genes involved in cell migration/motility and Golgi components. Abnormal Golgi apparatus and decreased expressions of genes involved in acrosome formation and lipid metabolism were detected in Ccdc157-deprived mouse germ cells. Interestingly, we attempted to treat infertile patients and Ccdc157 mutant mice with a Chinese medicine, Huangjin Zanyu, which improved the fertility in one patient and most mice that carried the heterozygous mutation in CCDC157. Healthy offspring were produced. Our study reveals CCDC157 is essential for sperm maturation and may serve as a marker for diagnosis of OAT.

Genetic mechanisms of fertilization failure and early embryonic arrest: a comprehensive review

BACKGROUND

Infertility and pregnancy loss are longstanding problems. Successful fertilization and high-quality embryos are prerequisites for an ongoing pregnancy. Studies have proven that every stage in the human reproductive process is regulated by multiple genes and any problem, at any step, may lead to fertilization failure (FF) or early embryonic arrest (EEA). Doctors can diagnose the pathogenic factors involved in FF and EEA by using genetic methods. With the progress in the development of new genetic technologies, such as single-cell RNA analysis and whole-exome sequencing, a new approach has opened up for us to directly study human germ cells and reproductive development. These findings will help us to identify the unique mechanism(s) that leads to FF and EEA in order to find potential treatments.

OBJECTIVE AND RATIONALE

The goal of this review is to compile current genetic knowledge related to FF and EEA, clarifying the mechanisms involved and providing clues for clinical diagnosis and treatment.

SEARCH METHODS

PubMed was used to search for relevant research articles and reviews, primarily focusing on English-language publications from January 1978 to June 2023. The search terms included fertilization failure, early embryonic arrest, genetic, epigenetic, whole-exome sequencing, DNA methylation, chromosome, non-coding RNA, and other related keywords. Additional studies were identified by searching reference lists. This review primarily focuses on research conducted in humans. However, it also incorporates relevant data from animal models when applicable. The results were presented descriptively, and individual study quality was not assessed.

OUTCOMES

A total of 233 relevant articles were included in the final review, from 3925 records identified initially. The review provides an overview of genetic factors and mechanisms involved in the human reproductive process. The genetic mutations and other genetic mechanisms of FF and EEA were systematically reviewed, for example, globozoospermia, oocyte activation failure, maternal effect gene mutations, zygotic genome activation abnormalities, chromosome abnormalities, and epigenetic abnormalities. Additionally, the review summarizes progress in treatments for different gene defects, offering new insights for clinical diagnosis and treatment.

WIDER IMPLICATIONS

The information provided in this review will facilitate the development of more accurate molecular screening tools for diagnosing infertility using genetic markers and networks in human reproductive development. The findings will also help guide clinical practice by identifying appropriate interventions based on specific gene mutations. For example, when an individual has obvious gene mutations related to FF, ICSI is recommended instead of IVF. However, in the case of genetic defects such as phospholipase C zeta1 (PLCZ1), actin-like7A (ACTL7A), actin-like 9 (ACTL9), and IQ motif-containing N (IQCN), ICSI may also fail to fertilize. We can consider artificial oocyte activation technology with ICSI to improve fertilization rate and reduce monetary and time costs. In the future, fertility is expected to be improved or restored by interfering with or supplementing the relevant genes.

CCDC189 affects sperm flagellum formation by interacting with CABCOCO1

Multiple morphological abnormalities of the sperm flagella (MMAF) are one of the major causes of male infertility and are characterized by multiple defects. In this study, we found that the coiled-coil domain-containing 189 (Ccdc189) gene was predominantly expressed in mouse testes and that inactivation of the Ccdc189 gene caused male infertility. Histological studies revealed that most sperm from Ccdc189-deficient mice carried coiled, curved or short flagella, which are typical MMAF phenotypes. Immunoelectron microscopy showed that the CCDC189 protein was located at the radial spoke of the first peripheral microtubule doublet in the sperm axoneme. A CCDC189-interacting protein, CABCOCO1 (ciliary-associated calcium-binding coiled-coil protein 1), was discovered via co-immunoprecipitation and mass spectrometry, and inactivation of Cabcoco1 caused malformation of sperm flagella, which was consistent with findings obtained with Ccdc189-deficient mice. Further studies revealed that inactivation of CCDC189 caused downregulation of CABCOCO1 protein expression and that both CCDC189 and CABCOCO1 interacted with the radial-spoke-specific protein RSPH1 and intraflagellar transport proteins. This study demonstrated that Ccdc189 is a radial-spoke-associated protein and is involved in sperm flagellum formation through its interactions with CABCOCO1 and intraflagellar transport proteins.

A novel mutation in CFAP47 causes male infertility due to multiple morphological abnormalities of the sperm flagella

Introduction

A previous study suggested that loss of CFAP47 function is involved in multiple morphological abnormalities of the sperm flagella (MMAF) in humans and mice. However, the comprehensive role of CFAP47 in spermatogenesis is largely unknown.

Methods

Whole-exome sequencing (WES) was conducted to identify pathogenic variant in two patients with MMAF. The functional effect of the identified mutations was investigated by immunofluorescence staining and western blotting. Intracytoplasmic sperm injection (ICSI) was used to assist fertilization for the patient with MMAF.

Results

In this study, we identified a novel missense mutation (c.1414G>A; p.V472M) in CFAP47 in two unrelated patients with oligoasthenoteratozoospermia. Intriguingly, in addition to the MMAF phenotype very analogous to the previous report, the two patients notably presented abnormal morphology of sperm heads, the sperm mitochondrial sheath was obviously disorganized, and the sperm annulus were almost defective. Further functional experiments confirmed that the expression of CFAP47 was markedly reduced in the spermatozoa of the patients. Mechanism analysis suggested that CFAP47 might regulate the expression of CFAP65, CFAP69 and SEPTIN4 through their physical interactions and thus modulating sperm morphogenesis.

Conclusion

we revealed a novel mutation in CFAP47 and further expanded the phenotype and mutation spectrum of CFAP47, as well as the potential mechanism of CFAP47 manipulating spermatogenesis, finally providing important guidance for genetic counseling and targeted treatment for CFAP47 mutation-related male infertility.

ARRDC5 expression is conserved in mammalian testes and required for normal sperm morphogenesis

In sexual reproduction, sperm contribute half the genomic material required for creation of offspring yet core molecular mechanisms essential for their formation are undefined. Here, the α-arrestin molecule arrestin-domain containing 5 (ARRDC5) is identified as an essential regulator of mammalian spermatogenesis. Multispecies testicular tissue transcriptome profiling indicates that expression of Arrdc5 is testis enriched, if not specific, in mice, pigs, cattle, and humans. Knockout of Arrdc5 in mice leads to male specific sterility due to production of low numbers of sperm that are immotile and malformed. Spermiogenesis, the final phase of spermatogenesis when round spermatids transform to spermatozoa, is defective in testes of Arrdc5 deficient mice. Also, epididymal sperm in Arrdc5 knockouts are unable to capacitate and fertilize oocytes. These findings establish ARRDC5 as an essential regulator of mammalian spermatogenesis. Considering the role of arrestin molecules as modulators of cellular signaling and ubiquitination, ARRDC5 is a potential male contraceptive target.

Molecular genetic mechanisms of teratozoospermia

In recent years, the incidence of teratospermia has been increasing, and it has become a very important factor leading to male infertility. The research on the molecular mechanism of teratospermia is also progressing rapidly. This article briefly summarizes the clinical incidence of teratozoospermia, and makes a retrospective summary of related studies reported in recent years. Specifically discussing the relationship between gene status and spermatozoa, the review aims to provide the basis for the genetic diagnosis and gene therapy of teratozoospermia.

Truncating PICK1 Variant Identified in Azoospermia Affected Mitochondrial Dysfunction in Knockout Mice

OBJECTIVE

The protein interacting with C kinase 1 (PICK1) plays a critical role in vesicle trafficking, and its deficiency in sperm cells results in abnormal vesicle trafficking from Golgi to acrosome, which eventually disrupts acrosome formation and leads to male infertility.

METHODS

An azoospermia sample was filtered, and the laboratory detection and clinical phenotype indicated typical azoospermia in the patient. We sequenced all of the exons in the PICK1 gene and found that there was a novel homozygous variant in the PICK1 gene, c.364delA (p.Lys122SerfsX8), and this protein structure truncating variant seriously affected the biological function. Then we constructed a PICK1 knockout mouse model using clustered regularly interspaced short palindromic repeat cutting technology (CRISPRc).

RESULTS

The sperm from PICK1 knockout mice showed acrosome and nucleus abnormalities, as well as dysfunctional mitochondrial sheath formation. Both the total sperm and motility sperm counts were decreased in the PICK1 knockout mice compared to wild-type mice. Moreover, the mitochondrial dysfunction was verified in the mice. These defects in the male PICK1 knockout mice may have eventually led to complete infertility.

CONCLUSION

The c.364delA novel variant in the PICK1 gene associated with clinical infertility, and pathogenic variants in the PICK1 may cause azoospermia or asthenospermia by impairing mitochondrial function in both mice and humans.

Human globozoospermia-related genes and their role in acrosome biogenesis

The mammalian acrosome is a secretory vesicle attached to the sperm nucleus whose fusion with the overlying plasma membrane is required to achieve fertilization. Acrosome biogenesis starts during meiosis, but it lasts through the entire process of haploid cell differentiation (spermiogenesis). Acrosome biogenesis is a stepwise process that involves membrane traffic from the Golgi apparatus, but it also seems that the lysosome/endosome system participates in this process. Defective sperm head morphology is accompanied by defective acrosome shape and function, and patients with these characteristics are infertile or subfertile. The most extreme case of acrosome biogenesis failure is globozoospermia syndrome, which is primarily characterized by the presence of round-headed spermatozoa without acrosomes with cytoskeleton defects around the nucleus and infertility. Several genes participating in acrosome biogenesis have been uncovered using genetic deletions in mice, but only a few of them have been found to be deleted or modified in patients with globozoospermia. Understanding acrosome biogenesis is crucial to uncovering the molecular basis of male infertility and developing new diagnostic tools and assisted reproductive technologies that may help infertile patients through more effective treatment techniques. This article is categorized under: Reproductive System Diseases > Environmental Factors Infectious Diseases > Stem Cells and Development Reproductive System Diseases > Molecular and Cellular Physiology.

Dynamic cellular and molecular characteristics of spermatogenesis in the viviparous marine teleost Sebastes schlegelii†

Spermatogenesis is a dynamic cell developmental process that is essential for reproductive success. Vertebrates utilize a variety of reproductive strategies, including sperm diversity, and internal and external fertilization. Research on the cellular and molecular dynamic changes involved in viviparous teleost spermatogenesis, however, is currently lacking. Here, we combined cytohistology, 10 × genomic single-cell RNA-seq, and transcriptome technology to determine the dynamic development characteristics of the spermatogenesis of Sebastes schlegelii. The expressions of lhcgr (Luteinizing hormone/Choriogonadotropin receptor), fshr (follicle-stimulating hormone receptor), ar (androgen receptor), pgr (progesterone receptor), and cox (cyclo-oxygen-ase), as well as the prostaglandin E and F levels peaked during the maturation period, indicating that they were important for sperm maturation and mating. Fifteen clusters were identified based on the 10 × genomic single-cell results. The cell markers of the sub-cluster were identified by their upregulation; piwil, dazl, and dmrt1 were upregulated and identified as spermatogonium markers, and sycp1/3 and spo11 were identified as spermatocyte markers. For S. schlegelii, the sperm head nucleus was elongated (spherical to streamlined in shape), which is a typical characteristic for sperm involved in internal fertilization. We also identified a series of crucial genes associated with spermiogenesis, such as spata6, spag16, kif20a, trip10, and klf10, while kif2c, kifap3, fez2, and spaca6 were found to be involved in nucleus elongation. The results of this study will enrich our cellular and molecular knowledge of spermatogenesis and spermiogenesis in fish that undergo internal fertilization.

Globozoospermia: A Case Report and Systematic Review of Literature

PURPOSE

Globozoospermia is a genetic syndrome characterized by the presence of round-headed spermatozoa and infertility due to the inability of these spermatozoa to fertilize the oocyte. In this article, we present the clinical case of a young globozoospermic patient with a new, not yet described mutation of the DPY19L2 gene. We also performed a systematic review of the literature on gene mutations, the outcome of assisted reproductive techniques, and the risk of transmission of abnormalities to the offspring in patients with globozoospermia and made recommendations to offer a more appropriate clinical management of these patients.

MATERIALS AND METHODS

We performed a systematic search in the PubMed, Google Scholar, and Scopus databases from their inception to December 2021. The search strategy included the combination of the following Medical Subjects Headings (MeSH) terms and keywords: "globozoospermia", "round-headed spermatozoa", "round head spermatozoa", "intracytoplasmic sperm injection", "ICSI", "offspring", "child health", "assisted reproductive technique outcome". All the eligible studies were selected following the PECOS (Population, Exposure, Comparison/Comparator, Outcomes, Study design) model. The quality of included studies was assessed by applying the "Cambridge Quality Checklists".

RESULTS

The main genes involved in the pathogenesis of globozoospermia are DPY19L2, SPATA16, PICK1, GGN, SPACA1, ZPBP, CCDC62, and CCNB3 genes. Other genes could also play a role. These include C2CD6, C7orf61, CCIN, DNH17, DNH6, PIWIL4, and CHPT1. Globozoospermic patients should undergo ART to achieve fertility. In particular, intracytoplasmic sperm injection with assisted oocyte activation or intracytoplasmic morphologically-selected sperm injection appears to be associated with a higher success rate. Patients with globozoospermia should also be evaluated for the high rate of sperm aneuploidy which appears to influence the success rate of ART but does not appear to be associated with an increased risk of transmission of genetic abnormalities to offspring.

CONCLUSIONS

This systematic review summarizes the evidence on the gene panel to be evaluated, ICSI outcomes, and the health of the offspring in patients with globozoospermia. Evidence-based recommendations on the management of patients with globozoospermia are provided.

Bud31-mediated alternative splicing is required for spermatogonial stem cell self-renewal and differentiation

Alternative splicing (AS) is tightly regulated during cell differentiation and development. AS events are prevalent in the testis, but the splicing regulation in spermatogenesis remains unclear. Here we report that the spliceosome component Bud31 plays a crucial role during spermatogenesis in mice. Germ cell-specific knockout of Bud31 led to loss of spermatogonia and to male infertility. We further demonstrate that Bud31 is required for both spermatogonial stem cell pool maintenance and the initiation of spermatogenesis. SMART-seq revealed that deletion of Bud31 in germ cells causes widespread exon-skipping and intron retention. Particularly, we identified Cdk2 as one of the direct splicing targets of Bud31, knockout of Bud31 resulted in retention of the first intron of Cdk2, which led to a decrease in Cdk2 expression. Our findings suggest that Bud31-mediated AS within spermatogonial stem cells regulates the self-renewal and differentiation of male germ cells in mammals.

Proteomic analysis of carp seminal plasma provides insights into the immune response to bacterial infection of the male reproductive system

Aeromonas salmonicida is recognized as a significant bacterial pathogen in ulcerative disease of cyprinid fish. However, the mechanism of immunity to these bacteria in common carp is still not well understood, especially the immune regulation in the gonad to bacterial infection. The aims of our study were to analyze changes in the seminal plasma proteome following A. salmonicida infection in carp males. The observed pathological changes in the tissue (liver, spleen, kidney and testis) morphology and upregulation of immune-related genes (tnfa2, il6a) confirmed the successful infection challenge. Using mass spectrometry-based label-free quantitative proteomics, we identified 1402 seminal plasma proteins, and 44 proteins (20 up- and 24 downregulated) were found to be differentially abundant between infected and control males. Most differentially abundant proteins were involved in the immune response mechanisms, such as acute phase response, complement activation and coagulation, inflammation, lipid metabolism, cell-cell and cell-matrix adhesion, creatine-phosphate biosynthesis and germ cell-Sertoli cell junction signaling. Bacterial infection also caused profound changes in expression of selected genes in the testis and hematopoietic organs, which contributed to changes in seminal proteins. The altered seminal proteins and bacterial proteins in seminal plasma may serve as valuable markers of infection in the testis.

Towards Post-Meiotic Sperm Production: Genetic Insight into Human Infertility from Mouse Models

Declined quality and quantity of sperm is currently the major cause of patients suffering from infertility. Male germ cell development is spatiotemporally regulated throughout the whole developmental process. While it has been known that exogenous factors, such as environmental exposure, diet and lifestyle, et al, play causative roles in male infertility, recent progress has revealed abundant genetic mutations tightly associated with defective male germline development. In mammals, male germ cells undergo dramatic morphological change (i.e., nuclear condensation) and chromatin remodeling during post-meiotic haploid germline development, a process termed spermiogenesis; However, the molecular machinery players and functional mechanisms have yet to be identified. To date, accumulated evidence suggests that disruption in any step of haploid germline development is likely manifested as fertility issues with low sperm count, poor sperm motility, aberrant sperm morphology or combined. With the continually declined cost of next-generation sequencing and recent progress of CRISPR/Cas9 technology, growing studies have revealed a vast number of disease-causing genetic variants associated with spermiogenic defects in both mice and humans, along with mechanistic insights partially attained and validated through genetically engineered mouse models (GEMMs). In this review, we mainly summarize genes that are functional at post-meiotic stage. Identification and characterization of deleterious genetic variants should aid in our understanding of germline development, and thereby further improve the diagnosis and treatment of male infertility.

The molecular mechanisms underlying acrosome biogenesis elucidated by gene-manipulated mice

Sexual reproduction requires the fusion of two gametes in a multistep and multifactorial process termed fertilization. One of the main steps that ensures successful fertilization is acrosome reaction. The acrosome, a special kind of organelle with a cap-like structure that covers the anterior portion of sperm head, plays a key role in the process. Acrosome biogenesis begins with the initial stage of spermatid development, and it is typically divided into four successive phases: the Golgi phase, cap phase, acrosome phase, and maturation phase. The run smoothly of above processes needs an active and specific coordination between the all kinds of organelles (endoplasmic reticulum, trans-golgi network and nucleus) and cytoplasmic structures (acroplaxome and manchette). During the past two decades, an increasingly genes have been discovered to be involved in modulating acrosome formation. Most of these proteins interact with each other and show a complicated molecular regulatory mechanism to facilitate the occurrence of this event. This Review focuses on the progresses of studying acrosome biogenesis using gene-manipulated mice and highlights an emerging molecular basis of mammalian acrosome formation.

Coiled-Coil Domain-Containing (CCDC) Proteins: Functional Roles in General and Male Reproductive Physiology

The coiled-coil domain-containing (CCDC) proteins have been implicated in a variety of physiological and pathological processes. Their functional roles vary from their interaction with molecular components of signaling pathways to determining the physiological functions at the cellular and organ level. Thus, they govern important functions like gametogenesis, embryonic development, hematopoiesis, angiogenesis, and ciliary development. Further, they are implicated in the pathogenesis of a large number of cancers. Polymorphisms in CCDC genes are associated with the risk of lifetime diseases. Because of their role in many biological processes, they have been extensively studied. This review concisely presents the functional role of CCDC proteins that have been studied in the last decade. Studies on CCDC proteins continue to be an active area of investigation because of their indispensable functions. However, there is ample opportunity to further understand the involvement of CCDC proteins in many more functions. It is anticipated that basing on the available literature, the functional role of CCDC proteins will be explored much further.

Exome sequencing reveals novel causes as well as new candidate genes for human globozoospermia

STUDY QUESTION

Can exome sequencing identify new genetic causes of globozoospermia?

SUMMARY ANSWER

Exome sequencing in 15 cases of unexplained globozoospermia revealed deleterious mutations in seven new genes, of which two have been validated as causing globozoospermia when knocked out in mouse models.

WHAT IS KNOWN ALREADY

Globozoospermia is a rare form of male infertility characterised by round-headed sperm and malformation of the acrosome. Although pathogenic variants in DPY19L2 and SPATA16 are known causes of globozoospermia and explain up to 70% of all cases, genetic causality remains unexplained in the remaining patients.

STUDY DESIGN, SIZE, DURATION

After pre-screening 16 men for mutations in known globozoospermia genes DPY19L2 and SPATA16, exome sequencing was performed in 15 males with globozoospermia or acrosomal hypoplasia of unknown aetiology.

PARTICIPANTS/MATERIALS, SETTING, METHOD

Targeted next-generation sequencing and Sanger sequencing was performed for all 16 patients to screen for single-nucleotide variants and copy number variations in DPY19L2 and SPATA16. After exclusion of one patient with DPY19L2 mutations, we performed exome sequencing for the 15 remaining subjects. We prioritised recessive and X-linked protein-altering variants with an allele frequency of <0.5% in the population database GnomAD in genes with an enhanced expression in the testis. All identified candidate variants were confirmed in patients and, where possible, in family members using Sanger sequencing. Ultrastructural examination of semen from one of the patients allowed for a precise phenotypic characterisation of abnormal spermatozoa.

MAIN RESULTS AND ROLE OF CHANCE

After prioritisation and validation, we identified possibly causative variants in eight of 15 patients investigated by exome sequencing. The analysis revealed homozygous nonsense mutations in ZPBP and CCDC62 in two unrelated patients, as well as rare missense mutations in C2CD6 (also known as ALS2CR11), CCIN, C7orf61 and DHNA17 and a frameshift mutation in GGN in six other patients. All variants identified through exome sequencing, except for the variants in DNAH17, were located in a region of homozygosity. Familial segregation of the nonsense variant in ZPBP revealed two fertile brothers and the patient’s mother to be heterozygous carriers. Paternal DNA was unavailable. Immunohistochemistry confirmed that ZPBP localises to the acrosome in human spermatozoa. Ultrastructural analysis of spermatozoa in the patient with the C7orf61 mutation revealed a mixture of round heads with no acrosomes (globozoospermia) and ovoid or irregular heads with small acrosomes frequently detached from the sperm head (acrosomal hypoplasia).

LIMITATIONS, REASONS FOR CAUTION

Stringent filtering criteria were used in the exome data analysis which could result in possible pathogenic variants remaining undetected. Additionally, functional follow-up is needed for several candidate genes to confirm the impact of these mutations on normal spermatogenesis.

WIDER IMPLICATIONS OF THE FINDINGS

Our study revealed an important role for mutations in ZPBP and CCDC62 in human globozoospermia as well as five new candidate genes. These findings provide a more comprehensive understanding of the genetics of male infertility and bring us closer to a complete molecular diagnosis for globozoospermia patients which would help to predict the success of reproductive treatments.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by The Netherlands Organisation for Scientific Research (918–15-667); National Health and Medical Research Council of Australia (APP1120356) and the National Council for Scientific Research (CONICET), Argentina, PIP grant 11220120100279CO. The authors have nothing to disclose.

Genetics of teratozoospermia: Back to the head

Spermatozoa are polarized cells with a head and a flagellum joined by the connecting piece. Head integrity is critical for normal sperm function, and head defects consistently lead to male infertility. Abnormalities of the sperm head are among the most severe and characteristic sperm defects. Patients presenting with a monomorphic head sperm defects such as globozoospermia or marcrozoospermia were analyzed permitting to identify several key genes for spermatogenesis such as AURKC and DPY19L2. The study of patients with other specific sperm head defects such as acephalic spermatozoa have also enabled the identification of new infertility genes such as SUN5. Here, we review the genetic causes leading to morphological defects of sperm head. Advances in the genetics of male infertility are necessary to improve the management of infertility and will pave the road towards future strategies of treatments, especially for patients with the most severe phenotype as sperm head defects.

Genes predisposing to syndromic and nonsyndromic infertility: a narrative review

Background

Advanced biological techniques have helped produce more insightful findings on the genetic etiology of infertility that may lead to better management of the condition. This review provides an update on genes predisposing to syndromic and nonsyndromic infertility.

Main body

The review identified 65 genes linked with infertility and infertility-related disorders. These genes regulate fertility. However, mutational loss of the functions of the genes predisposes to infertility. Twenty-three (23) genes representing 35% were linked with syndromic infertility, while 42 genes (65%) cause nonsyndromic infertility. Of the 42 nonsyndromic genes, 26 predispose to spermatogenic failure and sperm morphological abnormalities, 11 cause ovarian failures, and 5 cause sex reversal and puberty delay. Overall, 31 genes (48%) predispose to male infertility, 15 genes (23%) cause female infertility, and 19 genes (29%) predispose to both. The common feature of male infertility was spermatogenic failure and sperm morphology abnormalities, while ovarian failure has been the most frequently reported among infertile females. The mechanisms leading to these pathologies are gene-specific, which, if targeted in the affected, may lead to improved treatment.

Conclusions

Mutational loss of the functions of some genes involved in the development and maintenance of fertility may predispose to syndromic or nonsyndromic infertility via gene-specific mechanisms. A treatment procedure that targets the affected gene(s) in individuals expressing infertility may lead to improved treatment.

Molecular genetics of infertility: loss-of-function mutations in humans and corresponding knockout/mutated mice

BACKGROUND

Infertility is a major issue in human reproductive health, affecting an estimated 15% of couples worldwide. Infertility can result from disorders of sex development (DSD) or from reproductive endocrine disorders (REDs) with onset in infancy, early childhood or adolescence. Male infertility, accounting for roughly half of all infertility cases, generally manifests as decreased sperm count (azoospermia or oligozoospermia), attenuated sperm motility (asthenozoospermia) or a higher proportion of morphologically abnormal sperm (teratozoospermia). Female infertility can be divided into several classical types, including, but not limited to, oocyte maturation arrest, premature ovarian insufficiency (POI), fertilization failure and early embryonic arrest. An estimated one half of infertility cases have a genetic component; however, most genetic causes of human infertility are currently uncharacterized. The advent of high-throughput sequencing technologies has greatly facilitated the identification of infertility-associated gene mutations in patients over the past 20 years.

OBJECTIVE AND RATIONALE

This review aims to conduct a narrative review of the genetic causes of human infertility. Loss-of-function mutation discoveries related to human infertility are summarized and further illustrated in tables. Corresponding knockout/mutated animal models of causative genes for infertility are also introduced.

SEARCH METHODS

A search of the PubMed database was performed to identify relevant studies published in English. The term 'mutation' was combined with a range of search terms related to the core focus of the review: infertility, DSD, REDs, azoospermia or oligozoospermia, asthenozoospermia, multiple morphological abnormalities of the sperm flagella (MMAF), primary ciliary dyskinesia (PCD), acephalic spermatozoa syndrome (ASS), globozoospermia, teratozoospermia, acrosome, oocyte maturation arrest, POI, zona pellucida, fertilization defects and early embryonic arrest.

OUTCOMES

Our search generated ∼2000 records. Overall, 350 articles were included in the final review. For genetic investigation of human infertility, the traditional candidate gene approach is proceeding slowly, whereas high-throughput sequencing technologies in larger cohorts of individuals is identifying an increasing number of causative genes linked to human infertility. This review provides a wide panel of gene mutations in several typical forms of human infertility, including DSD, REDs, male infertility (oligozoospermia, MMAF, PCD, ASS and globozoospermia) and female infertility (oocyte maturation arrest, POI, fertilization failure and early embryonic arrest). The causative genes, their identified mutations, mutation rate, studied population and their corresponding knockout/mutated mice of non-obstructive azoospermia, MMAF, ASS, globozoospermia, oocyte maturation arrest, POI, fertilization failure and early embryonic arrest are further illustrated by tables. In this review, we suggest that (i) our current knowledge of infertility is largely obtained from knockout mouse models; (ii) larger cohorts of clinical cases with distinct clinical characteristics need to be recruited in future studies; (iii) the whole picture of genetic causes of human infertility relies on both the identification of more mutations for distinct types of infertility and the integration of known mutation information; (iv) knockout/mutated animal models are needed to show whether the phenotypes of genetically altered animals are consistent with findings in human infertile patients carrying a deleterious mutation of the homologous gene; and (v) the molecular mechanisms underlying human infertility caused by pathogenic mutations are largely unclear in most current studies.

WILDER IMPLICATIONS

It is important to use our current understanding to identify avenues and priorities for future research in the field of genetic causes of infertility as well as to apply mutation knowledge to risk prediction, genetic diagnosis and potential treatment for human infertility.

TBC1D20 deficiency induces Sertoli cell apoptosis by triggering irreversible endoplasmic reticulum stress in mice

Male 'blind sterile' mice with the causative TBC1 domain family member 20 (TBC1D20) deficiency are infertile with excessive germ cell apoptosis and spermatogenesis arrest at the spermatid stage. Sertoli cells are characterised as 'nurse cells' essential for normal spermatogenesis, but the role and corresponding molecular mechanisms of TBC1D20 deficiency in Sertoli cells of mice are not clear to date. In the present study, the histopathology of the testis and Sertoli cell proliferation and apoptosis were determined, and the corresponding molecular mechanisms were investigated by western blotting. Our data showed that TBC1D20 exhibits a testis-abundant expression pattern, and its expression level is positively associated with spermatogenesis. TBC1D20 is assembled in the Golgi and endoplasmic reticulum and is widely expressed by various germ cell subtypes and Sertoli cells. TBC1D20 deficiency in Sertoli cells led to an excessive apoptosis ratio and G1/S arrest. The increased apoptosis of TBC1D20-deficient Sertoli cells resulted from caspase-12 activation. TBC1D20-deficient Sertoli cells had an abnormal Golgi-endoplasmic reticulum structure, which led to endoplasmic reticulum stress, resulting in cell cycle arrest and excessive apoptosis. It suggested that TBC1D20 deficiency triggers irreversible endoplasmic reticulum stress resulting in G1/S arrest and excessive apoptosis in TBC1D20-deficient Sertoli cells, and TBC1D20 deficiency in Sertoli cells may also contribute to the infertility phenotype in 'blind sterile' male mice.

HIPK4 is essential for murine spermiogenesis

Mammalian spermiogenesis is a remarkable cellular transformation, during which round spermatids elongate into chromatin-condensed spermatozoa. The signaling pathways that coordinate this process are not well understood, and we demonstrate here that homeodomain-interacting protein kinase 4 (HIPK4) is essential for spermiogenesis and male fertility in mice. HIPK4 is predominantly expressed in round and early elongating spermatids, and Hipk4 knockout males are sterile, exhibiting phenotypes consistent with oligoasthenoteratozoospermia. Hipk4 mutant sperm have reduced oocyte binding and are incompetent for in vitro fertilization, but they can still produce viable offspring via intracytoplasmic sperm injection. Optical and electron microscopy of HIPK4-null male germ cells reveals defects in the filamentous actin (F-actin)-scaffolded acroplaxome during spermatid elongation and abnormal head morphologies in mature spermatozoa. We further observe that HIPK4 overexpression induces branched F-actin structures in cultured fibroblasts and that HIPK4 deficiency alters the subcellular distribution of an F-actin capping protein in the testis, supporting a role for this kinase in cytoskeleton remodeling. Our findings establish HIPK4 as an essential regulator of sperm head shaping and potential target for male contraception.

Toward Development of the Male Pill: A Decade of Potential Non-hormonal Contraceptive Targets

With the continued steep rise of the global human population, and the paucity of safe and practical contraceptive options available to men, the need for development of effective and reversible non-hormonal methods of male fertility control is widely recognized. Currently there are several contraceptive options available to men, however, none of the non-hormonal alternatives have been clinically approved. To advance progress in the development of a safe and reversible contraceptive for men, further identification of novel reproductive tract-specific druggable protein targets is required. Here we provide an overview of genes/proteins identified in the last decade as specific or highly expressed in the male reproductive tract, with deletion phenotypes leading to complete male infertility in mice. These phenotypes include arrest of spermatogenesis and/or spermiogenesis, abnormal spermiation, abnormal spermatid morphology, abnormal sperm motility, azoospermia, globozoospermia, asthenozoospermia, and/or teratozoospermia, which are all desirable outcomes for a novel male contraceptive. We also consider other associated deletion phenotypes that could impact the desirability of a potential contraceptive. We further discuss novel contraceptive targets underscoring promising leads with the objective of presenting data for potential druggability and whether collateral effects may exist from paralogs with close sequence similarity.

The Protein Phosphorylation Landscape of Mouse Spermatids during Spermiogenesis

The characteristic tadpole shape of sperm is formed from round spermatids via spermiogenesis, a process which results in dramatic morphological changes in the final stage of spermatogenesis in the testis. Protein phosphorylation, as one of the most important post-translational modifications, can regulate spermiogenesis; however, the phosphorylation events taking place during this process have not been systematically analyzed. In order to better understand the role of phosphorylation in spermiogenesis, large-scale phosphoproteome profiling is performed using IMAC and TiO₂ enrichment. In total, 13 835 phosphorylation sites, in 4196 phosphoproteins, are identified in purified mouse spermatids undergoing spermiogenesis in two biological replicates. Overall, 735 testis-specific proteins are identified to be phosphorylated, and are expressed at high levels during spermiogenesis. Gene ontology analysis shows enrichment of the identified phosphoproteins in terms of histone modification, cilium organization, centrosome and the adherens junction. Further characterization of the kinase-substrate phosphorylation network demonstrates enrichment of phosphorylation substrates related to the regulation of spermiogenesis. This global protein phosphorylation landscape of spermiogenesis shows wide phosphoregulation across a diverse range of processes during spermiogenesis and can help to further characterize the process of sperm generation. All MS data are available via ProteomeXchange with the identifier PXD011890.