Genetics of teratozoospermia: Back to the head

Genetic Causes of Qualitative Sperm Defects: A Narrative Review of Clinical Evidence

Several genes are implicated in spermatogenesis and fertility regulation, and these genes are presently being analysed in clinical practice due to their involvement in male factor infertility (MFI). However, there are still few genetic analyses that are currently recommended for use in clinical practice. In this manuscript, we reviewed the genetic causes of qualitative sperm defects. We distinguished between alterations causing reduced sperm motility (asthenozoospermia) and alterations causing changes in the typical morphology of sperm (teratozoospermia). In detail, the genetic causes of reduced sperm motility may be found in the alteration of genes associated with sperm mitochondrial DNA, mitochondrial proteins, ion transport and channels, and flagellar proteins. On the other hand, the genetic causes of changes in typical sperm morphology are related to conditions with a strong genetic basis, such as macrozoospermia, globozoospermia, and acephalic spermatozoa syndrome. We tried to distinguish alterations approved for routine clinical application from those still unsupported by adequate clinical studies. The most important aspect of the study was related to the correct identification of subjects to be tested and the correct application of genetic tests based on clear clinical data. The correct application of available genetic tests in a scenario where reduced sperm motility and changes in sperm morphology have been observed enables the delivery of a defined diagnosis and plays an important role in clinical decision-making. Finally, clarifying the genetic causes of MFI might, in future, contribute to reducing the proportion of so-called idiopathic MFI, which might indeed be defined as a subtype of MFI whose cause has not yet been revealed.

Spermatozoa in mice lacking the nucleoporin NUP210L show defects in head shape and motility but not in nuclear compaction or histone replacement

Biallelic loss-of-function mutation of NUP210L, encoding a testis-specific nucleoporin, has been reported in an infertile man whose spermatozoa show uncondensed heads and histone retention. Mice with a homozygous transgene intronic insertion in Nup210l were infertile but spermatozoa had condensed heads. Expression from this insertion allele is undefined, however, and residual NUP210L production could underlie the milder phenotype. To resolve this issue, we have created Nup210lem1Mjmm , a null allele of Nup210l, in the mouse. Nup210lem1Mjmm homozygotes show uniform mild anomalies of sperm head morphology and decreased motility, but nuclear compaction and histone removal appear unaffected. Thus, our mouse model does not support that NUP210L loss alone blocks spermatid nuclear compaction. Re-analyzing the patient's exome data, we identified a rare, potentially pathogenic, heterozygous variant in nucleoporin gene NUP153 (p.Pro485Leu), and showed that, in mouse and human, NUP210L and NUP153 colocalize at the caudal nuclear pole in elongating spermatids and spermatozoa. Unexpectedly, in round spermatids, NUP210L and NUP153 localisation differs between mouse (nucleoplasm) and human (nuclear periphery). Our data suggest two explanations for the increased phenotypic severity associated with NUP210L loss in human compared to mouse: a genetic variant in human NUP153 (p.Pro485Leu), and inter-species divergence in nuclear pore function in round spermatids.

Lack of CCDC146, a ubiquitous centriole and microtubule-associated protein, leads to non-syndromic male infertility in human and mouse

From a cohort of 167 infertile patients suffering from multiple morphological abnormalities of the flagellum (MMAF), pathogenic bi-allelic mutations were identified in the CCDC146 gene. In somatic cells, CCDC146 is located at the centrosome and at multiple microtubule-related organelles during mitotic division, suggesting that it is a microtubule-associated protein (MAP). To decipher the molecular pathogenesis of infertility associated with CCDC146 mutations, a Ccdc146 knock-out (KO) mouse line was created. KO male mice were infertile, and sperm exhibited a phenotype identical to CCDC146 mutated patients. CCDC146 expression starts during late spermiogenesis. In the spermatozoon, the protein is conserved but is not localized to centrioles, unlike in somatic cells, rather it is present in the axoneme at the level of microtubule doublets. Expansion microscopy associated with the use of the detergent sarkosyl to solubilize microtubule doublets suggests that the protein may be a microtubule inner protein (MIP). At the subcellular level, the absence of CCDC146 impacted all microtubule-based organelles such as the manchette, the head-tail coupling apparatus (HTCA), and the axoneme. Through this study, a new genetic cause of infertility and a new factor in the formation and/or structure of the sperm axoneme were characterized.

A loss-of-function variant in ZCWPW1 causes human male infertility with sperm head defect and high DNA fragmentation

BACKGROUND

Male infertility is a global health issue. The more causative genes related to human male infertility should be further explored. The essential role of Zcwpw1 in male mouse fertility has been established and the role of ZCWPW1 in human reproduction needs further investigation to verify.

METHODS

An infertile man with oligoasthenoteratozoospermia phenotype and his parents were recruited from West China Second University Hospital, Sichuan University. A total of 200 healthy Han Chinese volunteers without any evidence of infertility were recruited as normal controls, while an additional 150 infertile individuals were included to assess the prevalence of ZCWPW1 variants in a sporadic male sterile population. The causative gene variant was identified by Whole-exome sequencing and Sanger sequencing. The phenotype of the oligoasthenoteratozoospermia was determined by Papanicolaou staining, immunofluorescence staining and electron microscope. In-vitro experiments, western blot and in-silicon analysis were applied to assess the pathogenicity of the identified variant. Additionally, we examined the influence of the variant on the DNA fragmentation and DNA repair capability by Sperm Chromatin Dispersion and Neutral Comet Assay.

RESULTS

The proband exhibits a phenotype of oligoasthenoteratozoospermia, his spermatozoa show head defects by semen examination, Papanicolaou staining and electron microscope assays. Whole-exome sequencing and Sanger sequencing found the proband carries a homozygous ZCWPW1 variant (c.1064C > T, p. P355L). Immunofluorescence analysis shows a significant decrease in ZCWPW1 expression in the proband's sperm. By exogenous expression with ZCWPW1 mutant plasmid in vitro, the obvious declined expression of ZCWPW1 with the mutation is validated in HEK293T. After being treated by hydroxyurea, MUT-ZCWPW1 transfected cells and empty vector transfected cells have a higher level of γ-H2AX, increased tail DNA and reduced H3K9ac level than WT-ZCWPW1 transfected cells. Furthermore, the Sperm Chromatin Dispersion assay revealed the proband's spermatozoa have high DNA fragmentation.

CONCLUSIONS

It is the first report that a novel homozygous missense mutation in ZCWPW1 caused human male infertility with sperm head defects and high DNA fragmentation. This finding enriches the gene variant spectrum and etiology of oligoasthenoteratozoospermia.

Novel variations in TENT5D lead to teratozoospermia in infertile patients

PURPOSE

Teratozoospermia is the main pathogenic factor of male infertility. However, the genetic etiology of teratozoospermia is largely unknown. This study aims to clarify the relationship between novel variations in TENT5D and teratozoospermia in infertile patients.

MATERIALS AND METHODS

Two infertile patients were enrolled. Routine semen analysis of patients and normal controls was conducted with the WHO guidelines. Whole-exome sequencing (WES) was conducted to identify pathogenic variants in the two patients. Morphology and ultrastructure analysis of spermatozoa in the two patients was determined by Papanicolaou staining, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The functional effect of the identified variants was analyzed by immunofluorescence staining and western blotting. The expression of TENT5D in different germ cells was detected by immunofluorescence staining.

RESULTS

Two new hemizygous variations, c.101C > T (p.P34L) and c.125A > T (p.D42V), in TENT5D were detected in two patients with male infertility. Morphology analysis showed abnormalities in spermatozoa morphology in the two patients, including multiple heads, headless, multiple tails, coiled, and/or bent flagella. Ultrastructure analysis showed that most of the spermatozoa exhibited missing or irregularly arranged '9+2' structures. Further functional experiments confirmed the abrogated TENT5D protein expression in patients. In addition, both p.P34L and p.D42V substitutions resulted in a conformational change of the TENT5D protein. We precisely analyzed the subcellular localization of TENT5D in germ cells in humans and mice. And we found that TENT5D was predominantly detected in the head and flagellum of elongating spermatids and epididymal spermatozoa.

CONCLUSIONS

Our results showed further evidence of a relationship between TENT5D mutation and human male infertility, providing new genetic insight for use in the diagnosis and treatment of male infertility.

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.

The identification of AMZ2 as a candidate causative gene in a severe teratozoospermia patient characterized by vacuolated spermatozoa

Teratozoospermia with cephalic defects is one of the most severe types of sperm defects known to date. While several monogenic factors are linked to cephalic abnormalities, such as globozoospermia and macrozoospermia, the genetic cause of vacuolated spermatozoa remains inadequately described. Here, we analyzed whole-exome sequencing (WES) data for an individual from a consanguineous family with severely vacuolated spermatozoa. The analysis revealed a novel homozygous c.520A>G (p.Thr174Ala) variant in the archaelysin family metallopeptidase 2 (AMZ2), a gene that encodes a zinc metalloprotease previously shown to be highly expressed in the testes and sperm. Multiple algorithms predicted this variant to be a damaging mutation. Consistent with an autosomal recessive mode of inheritance, this variant was inherited from heterozygous parental carriers. To investigate the potential pathogenicity of the identified variant, we compared the AMZ2 expression in sperm cells from the patient with the AMZ2 variant and from a healthy control. Immunoblot analysis revealed that the homozygous missense variant in AMZ2 abolished AMZ2 expression in the spermatozoa. Our findings reveal a candidate causative gene for vacuolated spermatozoa.

Phytochemical consumption and the risk of teratozoospermia: findings from a hospital-based case-control study in China

STUDY QUESTION

Are dietary phytochemicals associated with the risk of teratozoospermia?

SUMMARY ANSWER

Dietary intake of carotene, including total carotene, α-carotene, β-carotene as well as retinol equivalent, and lutein + zeaxanthin, were inversely correlated with the risk of teratozoospermia.

WHAT IS KNOWN ALREADY

Phytochemicals are natural plant derived bioactive compounds, which have been reported to be potentially associated with male reproductive health. To date, no study has investigated the association between phytochemical intake and the risk of teratozoospermia.

STUDY DESIGN SIZE DURATION

This hospital-based case-control study, which included 146 newly diagnosed teratozoospermia cases and 581 controls with normozoospermia from infertile couples, was conducted in a hospital-based infertility clinic in China, from June 2020 to December 2020.

PARTICIPANTS/MATERIALS SETTING METHODS

Dietary information was collected using a validated semi-quantitative 110-item food frequency questionnaire. Unconditional logistic regression was applied to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between phytochemical (i.e. phytosterol, carotene, flavonoid, isoflavone, anthocyanidin, lutein + zeaxanthin, and resveratrol) intake and the risk of teratozoospermia.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed a decreased risk of teratozoospermia for the highest compared with the lowest tertile consumption of total carotene (OR = 0.40, 95% CI = 0.21-0.77), α-carotene (OR = 0.53, 95% CI = 0.30-0.93), β-carotene (OR = 0.47, 95% CI = 0.25-0.88), retinol equivalent (OR = 0.47, 95% CI = 0.24-0.90), and lutein + zeaxanthin (OR = 0.35, 95% CI = 0.19-0.66), with all of the associations showing evident linear trends (all P trend <0.05). In addition, significant dose-response associations were observed between campestanol and α-carotene consumption and the risk of teratozoospermia. Moreover, there was a significant multiplicative interaction between BMI and lutein + zeaxanthin intake (P interaction <0.05).

LIMITATIONS REASONS FOR CAUTION

The cases and controls were not a random sample of the entire target population, which could lead to admission rate bias. Nevertheless, the controls were enrolled from the same infertility clinic, which could reduce the bias caused by selection and increase the comparability. Furthermore, our study only included a Chinese population, therefore caution is required regarding generalization of our findings to other populations.

WIDER IMPLICATIONS OF THE FINDINGS

Dietary phytochemicals, namely carotene, lutein, and zeaxanthin, might exert a positive effect on teratozoospermia. These phytochemicals are common in the daily diet and dietary supplements, and thus may provide a preventive intervention for teratozoospermia.

STUDY FUNDING/COMPETING INTERESTS

This study was funded by Natural Science Foundation of Liaoning Province (No. 2022-MS-219 to X.B.W.), Outstanding Scientific Fund of Shengjing Hospital (No. M1150 to Q.J.W.), Clinical Research Cultivation Project of Shengjing Hospital (No. M0071 to B.C.P.), and JieBangGuaShuai Project of Liaoning Province (No. 2021JH1/1040050 to Y.H.Z.). All authors declared that there was no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

Contribution to a better analysis of spermatic and ultrasound testicular parameters in the follow-up of male infertility at the Histology Embryology Cytogenetic Laboratory of Cheikh Anta Diop University (UCAD)

INTRODUCTION

In Senegal, marital infertility is a real problem for society. We undertook the study of this subject to make an analysis of the spermatic parameters of the infertile Senegalese man and to better understand the impact of testicular morphological anomalies on male fertility.

PATIENTS AND METHODS

We conducted a cross-sectional, descriptive, retrospective study of 100 infertile patients followed at the Histology-Embryology-Cytogenetics laboratory of UCAD in Dakar, during the year 2020. Sperm parameters, presence of varicocele, and testicular volume were evaluated in our patients.

RESULTS/DISCUSSION

The mean age of the patients was 35.17±8.7 years. A history of sexually transmitted infections was found in 57% of patients. The mean duration of infertility was 5.67±3.2 years. The mean sperm count was 14,871,230/ml±4,950,000. Necrospermia was the most frequent abnormality found (60%), followed by asthenospermia (51%). The high rate of necrospermia could be explained by the high frequency of sexually transmitted infections. Other abnormalities were oligospermia (48%, including 09% cryptospermia), azoospermia (19%), teratospermia (19%), and hypospermia (13%). The predominance of azoospermia and oligospermia should prompt a search for a genetic predisposition in these subjects. The mean testicular volume was 10.3±4.9 cc on the right and 9.5±4.8 cc on the left. A single or bilateral varicocele was found in 43% of subjects. Patients with azoospermia and teratospermia were associated with testicular hypotrophy with a significant value (p=0.04).

CONCLUSION

Overall, the senegalese man consulting for infertility is a young adult, married for an average of 5 years. Necrospermia is the most frequently found anomaly. The severity of both qualitative and quantitative abnormalities should lead to a systematic search for a genetic origin. The etiological research of infertile patients must be done within a multidisciplinary framework to propose better management of these patients.

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.

Effects of six kinds of sperm staining methods on human sperm size and evaluation of their staining effects

BACKGROUND

Large- and small-headed sperm are common morphological abnormalities. If different sperm staining methods affect sperm size, they will make a difference in the accuracy of sperm morphological analysis results. In this case, the normal reference values of sperm head parameters for different staining methods should be established.

METHODS

Six sperm staining methods, including Papanicolaou, Diff-Quik, Shorr, Hematoxylin-eosin (HE), Wright, and Wright-Giemsa staining, were used to stain the sperm smears of 25 semen samples, respectively. Sperm head parameter's length (L), width (W), area (A), perimeter, acrosomal area (Ac), and the derived values L/W and Ac/A of 2500 sperm (100 for each specimen) per staining method were measured by a computer-aided sperm morphological analysis system.

RESULTS

The highest sperm head length and width were observed with the Wright-Giemsa and Wright staining, followed by the Diff-Quik. The lowest sperm head length and width were observed with the Papanicolaou staining, and the sperm head length and width of HE and Shorr staining were between those of Papanicolaou and Diff-Quik staining. There was the same trend in changes in sperm head area and perimeter. Diff-Quik and Shorr staining could clearly distinguish acrosome and nucleus, followed by HE staining, whereas the boundary between acrosome and nucleus was not evident in Papanicolaou, Wright, and Wright-Giemsa staining.

CONCLUSION

Different staining methods influence sperm size, and the normal reference values of sperm head parameters of each staining method should be established. Diff-Quik and Shorr staining may be suitable methods for routine sperm morphological analysis.

Hadh deficiency induced oligoasthenoteratozoospermia through the TNF-α/Bcl-2 pathway in male mice

The process of spermatogenesis is a complex and delicate process that is still not fully understood. In this study, we examined the role of fatty acid oxidase 3-hydroxy acyl CoA dehydrogenase (HADH) in maintaining normal spermatogenesis in mice. In male mice, ablation of the Hadh gene using CRISPR/Cas9 technology arrested spermatocyte meiosis, increased multinucleated giant germ cells and vacuoles in seminiferous tubules, and accompanied with acrosomal dysplasia. Hadh^-/- male mice showed the typical features of oligoasthenoteratozoospermia (OAT), including decreased sperm concentration and motility and increased sperm abnormalities. Next, we explored the molecular events in the testes of the mutant mice. We found fatty acids accumulated in the testis of Hadh^-/- mice. And also, inflammatory factors TNF-α, IL-1β, and IL-6 were significantly increased, apoptosis-related protein Bcl-2 was decreased, and Bax and cleaved-Caspase3 were increased in Hadh^-/- male mice testis. After using etanercept, a specific inhibitor of TNF-α, testis injury caused by Hadh knockout was significantly alleviated, the sperm quality and motility were improved, and germ cell apoptosis was reduced. So our study demonstrated that Hadh deletion caused an increase in fatty acids. The accumulated fatty acids further induced testicular inflammation and germ cell apoptosis through the TNF-α/Bcl-2 signaling pathway, finally resulting in OAT in the Hadh^-/- mice. Inhibiting TNF-α may be used as a new treatment approach for testicular inflammation and OAT.

Mutations in CCIN cause teratozoospermia and male infertility

Teratozoospermia is usually associated with defective spermiogenesis and is a disorder with considerable genetic heterogeneity. Although previous studies have identified several teratozoospermia-associated genes, the etiology remains unknown for a majority of affected men. Here, we identified a homozygous missense mutation and a compound heterozygous mutation of CCIN in patients suffering from teratozoospermia. CCIN encodes the cytoskeletal protein Calicin that is involved in the formation and maintenance of the highly regular organization of the calyx of mammalian spermatozoa, and has been proposed to play a role in sperm head structure remodeling during the process of spermiogenesis. Our morphological and ultrastructural analyses of the spermatozoa obtained from all three men harboring deleterious CCIN mutants reveal severe head malformation. Further immunofluorescence assays unveil markedly reduced levels of Calicin in spermatozoa. These patient phenotypes are successfully recapitulated in mouse models expressing the disease-associated variants, confirming the role of Calicin in male fertility. Notably, all mutant spermatozoa from mice and human patients fail to adhere to the zona mass, which likely is the major mechanistic reason for CCIN-mutant sperm-derived infertility. Finally, the use of intra-cytoplasmic sperm injections (ICSI) successfully makes mutated mice and two couples with CCIN variants have healthy offspring. Taken together, our findings identify the role of Calicin in sperm head shaping and male fertility, providing important guidance for genetic counseling and assisted reproduction treatments.

The relevance of sperm morphology in male infertility

This brief report concerns the role of human sperm morphology assessment in different fields of male infertility: basic research, genetics, assisted reproduction technologies, oxidative stress. One of the best methods in studying sperm morphology is transmission electron microscopy (TEM) that enables defining the concept of sperm pathology and classifying alterations in non-systematic and systematic. Non-systematic sperm defects affect head and tail in variable ratio, whereas the rare systematic defects are characterized by a particular anomaly that marks most sperm of an ejaculate. TEM analysis and fluorescence in situ hybridization represent outstanding methods in the study of sperm morphology and cytogenetic in patients with altered karyotype characterizing their semen quality before intracytoplasmic sperm injection. In recent years, the genetic investigations on systematic sperm defects, made extraordinary progress identifying candidate genes whose mutations induce morphological sperm anomalies. The question if sperm morphology has an impact on assisted fertilization outcome is debated. Nowadays, oxidative stress represents one of the most important causes of altered sperm morphology and function and can be analyzed from two points of view: 1) spermatozoa with cytoplasmic residue produce reactive oxygen species, 2) the pathologies with inflammatory/oxidative stress background cause morphological alterations. Finally, sperm morphology is also considered an important endpoint in in vitro experiments where toxic substances, drugs, antioxidants are tested. We think that the field of sperm morphology is far from being exhausted and needs other research. This parameter can be still considered a valuable indicator of sperm dysfunction both in basic and clinical research.

Pathogenic variant in ACTL7A causes severe teratozoospermia characterized by bubble-shaped acrosomes and male infertility

Teratozoospermia is a common factor associated with male infertility. However, teratozoospermia characterized by bubble-shaped acrosomes (BSAs) has not yet been identified in men and the causative genes are unknown. The present study is of a patient with severe teratozoospermia characterized by BSA and carrying a variant (c.1204G>A, p. Gly402Ser) of actin-like 7A (ACTL7A). For further verification, we generated an Actl7a-mutated mouse model (p.Gly407Ser) carrying an equivalent variant to that in the patient. We found that homozygous Actl7a-mutated (Actl7aMut/Mut) male mice were sterile, and all their sperm showed acrosomal abnormalities. We detected, by transmission electron microscopy, that during acrosomal biogenesis the acrosome detaches from the nuclear membrane in Actl7aMut/Mut mice. Furthermore, mutant ACTL7A failed to attach to the acroplaxome and was discharged by cytoplasmic droplets, which led to the absence of ACTL7A in epididymal spermatozoa in mice. The mutant sperm failed to activate the oocyte, and sperm-borne oocyte activation factor PLCζ discharge accompanied by ACTL7A was observed, leading to total fertilization failure (TFF). Immunoprecipitation followed by liquid chromatography-mass spectrometry showed that several differentially expressed proteins participate in acrosome assembly and actin filament organization. Furthermore, assisted oocyte activation by calcium ionophore exposure successfully overcame TFF in the couple with an ACTL7A pathogenic variant. Our study defined a novel phenotype of an acrosomal abnormality characterized by BSA, revealed the underlying mechanism of a pathogenic variant in ACTL7A, and provided a genetic marker and potential therapeutic option for male infertility.

Oligogenic heterozygous inheritance of sperm abnormalities in mouse

Male infertility is an important health concern that is expected to have a major genetic etiology. Although high-throughput sequencing has linked gene defects to more than 50% of rare and severe sperm anomalies, less than 20% of common and moderate forms are explained. We hypothesized that this low success rate could at least be partly due to oligogenic defects – the accumulation of several rare heterozygous variants in distinct, but functionally connected, genes. Here, we compared fertility and sperm parameters in male mice harboring one to four heterozygous truncating mutations of genes linked to multiple morphological anomalies of the flagellum (MMAF) syndrome. Results indicated progressively deteriorating sperm morphology and motility with increasing numbers of heterozygous mutations. This first evidence of oligogenic inheritance in failed spermatogenesis strongly suggests that oligogenic heterozygosity could explain a significant proportion of asthenoteratozoospermia cases. The findings presented pave the way to further studies in mice and man.

Sperm bauplan and function and underlying processes of sperm formation and selection

The spermatozoon is a highly differentiated and polarized cell, with two main structures: the head, containing a haploid nucleus and the acrosomal exocytotic granule, and the flagellum, which generates energy and propels the cell; both structures are connected by the neck. The sperm's main aim is to participate in fertilization, thus activating development. Despite this common bauplan and function, there is an enormous diversity in structure and performance of sperm cells. For example, mammalian spermatozoa may exhibit several head patterns and overall sperm lengths ranging from ∼30 to 350 µm. Mechanisms of transport in the female tract, preparation for fertilization, and recognition of and interaction with the oocyte also show considerable variation. There has been much interest in understanding the origin of this diversity, both in evolutionary terms and in relation to mechanisms underlying sperm differentiation in the testis. Here, relationships between sperm bauplan and function are examined at two levels: first, by analyzing the selective forces that drive changes in sperm structure and physiology to understand the adaptive values of this variation and impact on male reproductive success and second, by examining cellular and molecular mechanisms of sperm formation in the testis that may explain how differentiation can give rise to such a wide array of sperm forms and functions.

Combined Use of Whole Exome Sequencing and CRISPR/Cas9 to Study the Etiology of Non-Obstructive Azoospermia: Demonstration of the Dispensable Role of the Testis-Specific Genes C1orf185 and CCT6B

The genetic landscape of male infertility is highly complex. It is estimated that at least 4000 genes are involved in human spermatogenesis, but only few have so far been extensively studied. In this study, we investigated by whole exome sequencing two cases of idiopathic non-obstructive azoospermia (NOA) due to severe hypospermatogenesis. After variant filtering and prioritizing, we retained for each patient a homozygous loss-of-function (LoF) variant in a testis-specific gene, C1orf185 (c.250C>T; p.Gln84Ter) and CCT6B (c.615-2A>G), respectively. Both variants are rare according to the gnomAD database and absent from our local control cohort (n = 445). To verify the implication of these candidate genes in NOA, we used the CRISPR/Cas9 system to invalidate the mouse orthologs 4930522H14Rik and Cct6b and produced two knockout (KO) mouse lines. Sperm and testis parameters of homozygous KO adult male mice were analyzed and compared with those of wild-type animals. We showed that homozygous KO males were fertile and displayed normal sperm parameters and a functional spermatogenesis. Overall, these results demonstrate that not all genes highly and specifically expressed in the testes are essential for spermatogenesis, and in particular, we conclude that bi-allelic variants of C1orf185 and CCT6B are most likely not to be involved in NOA and male fertility.

Semen analysis: a workflow for an appropriate assessment of the male fertility status

Infertility is a worldwide problem that affects 9-15% of couples of reproductive age. In about half of the cases, it recognizes, alone or in combination, a male cause. In addition to a reproductive problem, male infertility can result from a systemic disease. Consequently, semen analysis, a fundamental test in the diagnosis of male infertility, represents a useful indicator not only of a man's reproductive capacity but also of his health and lifestyle. Given the key role of semen analysis, only accredited laboratories should perform it and experienced clinicians should be called into play in its interpretation. In this article, we have extensively examined how the macroscopic and microscopic parameters of semen analysis, alone or associated with each other, allow clinicians to orient towards specific diagnoses that can be confirmed by further ad hoc tests. On this basis, we also proposed a diagnostic flowchart focused on the results of the semen analysis.

Identification and Characterization of the Most Common Genetic Variant Responsible for Acephalic Spermatozoa Syndrome in Men Originating from North Africa

Acephalic spermatozoa syndrome (ASS) is a rare but extremely severe type of teratozoospermia, defined by the presence of a majority of headless flagella and a minority of tail-less sperm heads in the ejaculate. Like the other severe monomorphic teratozoospermias, ASS has a strong genetic basis and is most often caused by bi-allelic variants in SUN5 (Sad1 and UNC84 domain-containing 5). Using whole exome sequencing (WES), we investigated a cohort of nine infertile subjects displaying ASS. These subjects were recruited in three centers located in France and Tunisia, but all originated from North Africa. Sperm from subjects carrying candidate genetic variants were subjected to immunofluorescence analysis and transmission electron microscopy. Moreover, fluorescent in situ hybridization (FISH) was performed on sperm nuclei to assess their chromosomal content. Variant filtering permitted us to identify the same SUN5 homozygous frameshift variant (c.211+1_211+2dup) in 7/9 individuals (78%). SUN5 encodes a protein localized on the posterior part of the nuclear envelope that is necessary for the attachment of the tail to the sperm head. Immunofluorescence assays performed on sperm cells from three mutated subjects revealed a total absence of SUN5, thus demonstrating the deleterious impact of the identified variant on protein expression. Transmission electron microscopy showed a conserved flagellar structure and a slightly decondensed chromatin. FISH did not highlight a higher rate of chromosome aneuploidy in spermatozoa from SUN5 patients compared to controls, indicating that intra-cytoplasmic sperm injection (ICSI) can be proposed for patients carrying the c.211+1_211+2dup variant. These results suggest that the identified SUN5 variant is the main cause of ASS in the North African population. Consequently, a simple and inexpensive genotyping of the 211+1_211+2dup variant could be beneficial for affected men of North African origin before resorting to more exhaustive genetic analyses.

Novel Loss-of-Function Mutations in DNAH1 Displayed Different Phenotypic Spectrum in Humans and Mice

Male infertility is a prevalent disorder distressing an estimated 70 million people worldwide. Despite continued progress in understanding the causes of male infertility, idiopathic sperm abnormalities such as multiple morphological abnormalities of sperm flagella (MMAF) still account for about 30% of male infertility. Recurrent mutations in DNAH1 have been reported to cause MMAF in various populations, but the underlying mechanism is still poorly explored. This study investigated the MMAF phenotype of two extended consanguineous Pakistani families without manifesting primary ciliary dyskinesia symptoms. The transmission electron microscopy analysis of cross-sections of microtubule doublets revealed a missing central singlet of microtubules and a disorganized fibrous sheath. SPAG6 staining, a marker generally used to check the integration of microtubules of central pair, further confirmed the disruption of central pair in the spermatozoa of patients. Thus, whole-exome sequencing (WES) was performed, and WES analysis identified two novel mutations in the DNAH1 gene that were recessively co-segregating with MMAF phenotype in both families. To mechanistically study the impact of identified mutation, we generated Dnah1 mice models to confirm the in vivo effects of identified mutations. Though Dnah1^{△iso1/△iso1} mutant mice represented MMAF phenotype, no significant defects were observed in the ultrastructure of mutant mice spermatozoa. Interestingly, we found DNAH1 isoform2 in Dnah1^{△iso1/△iso1} mutant mice that may be mediating the formation of normal ultrastructure in the absence of full-length protein. Altogether we are first reporting the possible explanation of inconsistency between mouse and human DNAH1 mutant phenotypes, which will pave the way for further understanding of the underlying pathophysiological mechanism of MMAF.