PDCL2 is essential for sperm acrosome formation and male fertility in mice

BACKGROUND

Each year, infertility affects 15% of couples worldwide, with 50% of cases attributed to men. Globozoospermia is an uncommon cause of male factor infertility, characterized by defects in sperm acrosome formation, leading to round-headed spermatozoa.

OBJECTIVE

We generated Pdcl2 knockout mice to investigate the essential roles of PDCL2 in mammalian reproduction.

MATERIALS AND METHODS

We used reverse transcription-polymerase chain reaction to demonstrate that PDCL2 was expressed exclusively in the male reproductive tract in mice and humans. We created Pdcl2 knockout mice using the CRISPR-Cas9 system and analyzed their fertility. Pdcl2 null spermatozoa underwent further evaluation using computer-assisted sperm analysis, light microscopy, and ultrastructural microscopy. We used immunoblot analysis and immunofluorescence to elucidate relationships between PDCL2 and other acrosomal proteins.

RESULTS

The PDC family is highly conserved in eukaryotes. Mouse and human PDCL2 are testis enriched and localized to the testicular endoplasmic reticulum. Loss of the protein causes sterility because of abnormal acrosome biogenesis during spermiogenesis and immotility. Furthermore, Pdcl2 null spermatozoa have rounded heads, similar to globozoospermia in humans. Observation of the knockout testis shows a lack of acrosomal cap formation, aberrant localization of mitochondria in the sperm head, and misshapen nuclei.

CONCLUSION

PDCL2 is essential for sperm acrosome development and male fertility in mice and is a putative contraceptive target in men.

Awareness and reporting of globozoospermia among in vitro fertilization and andrology laboratories: A national survey

Globozoospermia (GZ) is a rare disorder found in less than 0.1% of infertile men in which spermatozoa lack acrosomes necessary for penetration of an oocyte. While methods have been demonstrated to allow globozoospermic men to achieve a viable pregnancy with their partner, the Wold Health Organization considers identifying and reporting GZ on semen analysis to be 'important'. Our study aims to determine if and to what extent in vitro fertilization (IVF) laboratories nationwide recognize and report GZ on semen analysis reports. We constructed an IRB-approved survey sent nationwide to IVF and andrology clinic laboratory directors listed by the Society for Assisted Reproductive Technology and/or the American Society for Reproductive Medicine. Results from the survey were de-identified for analysis. A total of 490 surveys were sent with a response rate of 10% (n = 51). Most respondents (66%) practiced in a private, rather than academic, setting. A majority of respondents were confident in their technicians' knowledge of GZ (86%) and ability to identify it on a sample (94%). However, only half of respondents noted a space to report the concern for GZ to the ordering physician, and 25% of respondents did not feel their clinic was able to identify patients where there is a concern for GZ. Similarly, 84% of respondents did not report a percent of acrosome-deficient sperm. Less than half of respondents reported that their clinic has previously diagnosed GZ. Though the majority of respondents felt that their laboratory technicians would be able to identify GZ, a significant minority felt that their clinic did not have means to be able to report concern for GZ. This may be due to the absence of a proper channel to report a concern for GZ, a lack of knowledge about the condition, or failure to distinguish GZ from a broader reported percentage of morphologically abnormal sperm. Given evidence that the diagnosis of GZ may be under-reported in the United States, there should be a national standard for laboratory technicians to be trained to recognize GZ and be able to report their suspicion to the ordering clinician.

Healthy birth in a case of total globozoospermia after intracytoplasmic sperm injection and assisted oocyte activation

Globozoospermia is a rare (incidence <0.1%) and very severe disorder, with major implications in male fertility. Total globozoospermia is represented by the presence of spermatozoa with 100% rounded heads and a lack of acrosomes. These specific morphological modifications seem to be connected to defects occurring in the last stage of spermatogenesis, spermiogenesis, and will result in anomalies of the acrosomal reaction and a defective adherence of the spermatozoa to the oocytes zona pellucida. This will result in a failure of natural fertilization. This article aims to present the case of a couple diagnosed and successfully treated for primary male infertility. The 26-year-old male partner underwent two semen analyses that revealed the presence of fully rounded spermatozoa heads (morphological abnormality) and consequently was proposed for in vitro fertilization treatment. Semen preparation and the use of assisted reproductive techniques, intracytoplasmic injection of sperm cells into the assisted oocyte activation, have resulted in the conceivement of a healthy child. The particularities of this case lie in the early recognition of the total abnormal globozoospermia morphology. This is the first case reported in Romania where specific assisted reproductive techniques and treatments have resulted in a successful pregnancy for a couple with male total globozoospermia.

Translational aspects of novel findings in genetics of male infertility-status quo 2021

INTRODUCTION

Male factor infertility concerns 7-10% of men and among these 40-60% remain unexplained.

SOURCES OF DATA

This review is based on recent published literature regarding the genetic causes of male infertility.

AREAS OF AGREEMENT

Screening for karyotype abnormalities, biallelic pathogenic variants in the CFTR gene and Y-chromosomal microdeletions have been routine in andrology practice for >20 years, explaining ~10% of infertility cases. Rare specific conditions, such as congenital hypogonadotropic hypogonadism, disorders of sex development and defects of sperm morphology and motility, are caused by pathogenic variants in recurrently affected genes, which facilitate high diagnostic yield (40-60%) of targeted gene panel-based testing.

AREAS OF CONTROVERSY

Progress in mapping monogenic causes of quantitative spermatogenic failure, the major form of male infertility, has been slower. No 'recurrently' mutated key gene has been identified and worldwide, a few hundred patients in total have been assigned a possible monogenic cause.

GROWING POINTS

Given the high genetic heterogeneity, an optimal approach to screen for heterogenous genetic causes of spermatogenic failure is sequencing exomes or in perspective, genomes. Clinical guidelines developed by multidisciplinary experts are needed for smooth integration of expanded molecular diagnostics in the routine management of infertile men.

AREAS TIMELY FOR DEVELOPING RESEARCH

Di-/oligogenic causes, structural and common variants implicated in multifactorial inheritance may explain the 'hidden' genetic factors. It is also critical to understand how the recently identified diverse genetic factors of infertility link to general male health concerns across lifespan and how the clinical assessment could benefit from this knowledge.

Zona Pellucida sperm-binding protein 3 receptor distribution during Gopc-/- globozoospermic spermatogenesis

Globozoospermia is a type of teratozoospermia characterized by round morphology of the sperm head. Gopc^-/- infertile globozoospermic murine model has failures during spermiogenesis, such as the incorrect biogenesis of the acrosome, disorganized acroplaxome and manchette, round nuclei and spiral flagella. In this study, Western blot, RT-PCR, immunohistochemistry and immunogold were done for the localization of the acrosome protein Zona Pellucida sperm-binding protein 3 receptor (ZP3R), also called sp56, in wild type and Gopc^-/- mice testis. The ZP3R protein was located in the acrosome and pseudo-acrosome vesicles of wild type and Gopc^-/- mice, respectively. Also, it is distributed through the cytoplasm of the haploid spermatids only. The incorrect spermiogenesis of Gopc^-/- mice causes a deregulation in the expression of ZP3R in the globozoospermic spermatids. Our results suggest that although the lack of GOPC causes a failure during the transport of the pre-acrosomal vesicles, the acrosome protein ZP3R is localized in the acrosome and is distributed through the cytoplasm only during spermiogenesis. Furthermore, the failure in spermiogenesis does not impair the synthesis of ZP3R and its localization in the pre-acrosomal vesicles.

Loss of Profilin3 Impairs Spermiogenesis by Affecting Acrosome Biogenesis, Autophagy, Manchette Development and Mitochondrial Organization

Profilins (PFNs) are key regulatory proteins for the actin polymerization in cells and are encoded in mouse and humans by four Pfn genes. PFNs are involved in cell mobility, cell growth, neurogenesis, and metastasis of tumor cells. The testes-specific PFN3 is localized in the acroplaxome-manchette complex of developing spermatozoa. We demonstrate that PFN3 further localizes in the Golgi complex and proacrosomal vesicles during spermiogenesis, suggesting a role in vesicle transport for acrosome formation. Using CRISPR/Cas9 genome editing, we generated mice deficient for Pfn3. Pfn3-/- males are subfertile, displaying a type II globozoospermia. We revealed that Pfn3-/- sperm display abnormal manchette development leading to an amorphous sperm head shape. Additionally, Pfn3-/- sperm showed reduced sperm motility resulting from flagellum deformities. We show that acrosome biogenesis is impaired starting from the Golgi phase, and mature sperm seems to suffer from a cytoplasm removal defect. An RNA-seq analysis revealed an upregulation of Trim27 and downregulation of Atg2a. As a consequence, mTOR was activated and AMPK was suppressed, resulting in the inhibition of autophagy. This dysregulation of AMPK/mTOR affected the autophagic flux, which is hallmarked by LC3B accumulation and increased SQSTM1 protein levels. Autophagy is involved in proacrosomal vesicle fusion and transport to form the acrosome. We conclude that this disruption leads to the observed malformation of the acrosome. TRIM27 is associated with PFN3 as determined by co-immunoprecipitation from testis extracts. Further, actin-related protein ARPM1 was absent in the nuclear fraction of Pfn3-/- testes and sperm. This suggests that lack of PFN3 leads to destabilization of the PFN3-ARPM1 complex, resulting in the degradation of ARPM1. Interestingly, in the Pfn3-/- testes, we detected increased protein levels of essential actin regulatory proteins, cofilin-1 (CFL1), cofilin-2 (CFL2), and actin depolymerizing factor (ADF). Taken together, our results reveal the importance for PFN3 in male fertility and implicate this protein as a candidate for male factor infertility in humans.

Molecular Analysis of DPY19L2, PICK1 and SPATA16 in Italian Unrelated Globozoospermic Men

This study aims to evaluate genetic contribution and sperm DNA fragmentation (SDF) in a cohort of 18 unrelated globozoospermic Italian men (Group G). Semen samples were assessed according to the WHO 2010 Laboratory Manual and compared with 31 fertile controls. We focused our genetic analysis on the exons of the main globozoospermia-associated genes, performing qualitative PCR to assess deletion of DPY19L2 and sequencing to detect mutations of SPATA16 and PICK1. SDF was evaluated using the TUNEL assay. In Group G, 10 patients had a complete form of globozoospermia, whereas 8 patients had a partial form. Molecular analysis revealed deletion of DPY19L2 in six of the patients, all of them with complete globozoospermia, while no mutations were found in the examined exons of PICK1 and SPATA16. TUNEL analysis showed a higher SDF% in Group G. Our findings confirm DPY19L2 defects as the most frequent genetic alteration in Italian patients contributing to globozoospermic phenotypes. Furthermore, spermatozoa with acrosomal defects could also display high levels of SDF as a possible consequence of abnormally remodeled chromatin. The possible effect on offspring of chromatin structure abnormalities and altered DNA integrity should be carefully evaluated by clinicians, especially regarding the feasibility and safety of artificial reproductive techniques, which represent the only treatment that allows these patients to conceive.

Loss of SPACA1 function causes autosomal recessive globozoospermia by damaging the acrosome-acroplaxome complex

STUDY QUESTION

Is the sperm acrosome membrane-associated protein 1 (SPACA1) gene critical to human globozoospermia?

SUMMARY ANSWER

The biallelic loss-of-function (variant of SPACA1) causes globozoospermia as a result of acrosome-acroplaxome complex damage.

WHAT IS KNOWN ALREADY

SPACA1 expression decreases in patients with globozoospermia. Spaca1 gene-disrupted mice have abnormally shaped sperm heads that resemble those of human globozoospermia.

STUDY DESIGN, SIZE, DURATION

We recruited a consanguineous family with two brothers affected by infertility as a consequence of globozoospermia. The semen analysis data and ART outcomes were collected. Exome sequencing (ES) was used to identify potential pathogenic variants. Protein-protein interaction (PPI) technologies and proteomic analysis were utilized to explore the pathogenic mechanism.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two globozoospermic brothers and their consanguineous parents were recruited to identify the potential pathogenic variant through ES. A homozygous nonsense variant in the SPACA1 gene in both brothers inherited from the heterozygous parents was identified. Twenty normal fertile males were recruited as controls. Sperm ultrastructure was observed with transmission electron microscopy. Western blotting was performed to measure SPACA1 expression level in the sperm from the patients. Mass spectrometry (MS) analyses were used to identify differentially expressed proteins and to investigate proteins that interact with SPACA1. Co-immunoprecipitation (co-IP), yeast two-hybrid (Y2H) and immunofluorescence colocalization assays were used to confirm the PPI.

MAIN RESULTS AND THE ROLE OF CHANCE

A nonsense variant (NM_030960.2: c.53G>A; p. Trp18*) in the SPACA1 gene was identified as the pathogenic variant in a family with globozoospermia. Patient IV:1 and Patient IV:2 had a phenotype very similar to that of Spaca1 gene-disrupted mice. The nonsense variant in SPACA1 led to premature transcriptional termination in the signal peptide, which was confirmed by western blotting. MS-based proteomics analysis showed that eight interactors of SPACA1 were differentially expressed in the patients' sperm, including actin-like Protein 7A (ACTL7A), an important component of the acrosome-acroplaxome complex. The PPI of SPACA1 and ACTL7A was confirmed via co-IP and Y2H assays. Immunofluorescence showed that SPACA1 and ACTL7A colocalized in mature sperm, revealing that these proteins were coexpressed spatially.

LIMITATIONS, REASONS FOR CAUTION

Given the rarity of globozoospermia, only two patients from one family harbouring the SPACA1 variant were found. Future studies should evaluate SPACA1 variants in larger cohorts to corroborate this finding.

WIDER IMPLICATIONS OF THE FINDINGS

This study revealed that the SPACA1 gene was critical for globozoospermia, which expanded the spectrum of causative genes for globozoospermia. This study also provided evidence for ICSI clinical outcomes for patients with SPACA1-deficient globozoospermia, which may guide clinical treatment strategies. Furthermore, this study explored the pathogenesis of globozoospermia caused by SPACA1 deficiency.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the Precision Medical Research of National Key Research and Development Program (2018YFC1002400), National Natural Science Foundation of China (81873724), and Natural Science Foundation of Shanghai (20ZR1472700). The authors have no conflicts of interest to disclose.

TRIAL REGISTRATION NUMBER

N/A.

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.

Identification of a New QTL Region on Mouse Chromosome 1 Responsible for Male Hypofertility: Phenotype Characterization and Candidate Genes

Male fertility disorders often have their origin in disturbed spermatogenesis, which can be induced by genetic factors. In this study, we used interspecific recombinant congenic mouse strains (IRCS) to identify genes responsible for male infertility. Using ultrasonography, in vivo and in vitro fertilization (IVF) and electron microscopy, the phenotyping of several IRCS carrying mouse chromosome 1 segments of Mus spretus origin revealed a decrease in the ability of sperm to fertilize. This teratozoospermia included the abnormal anchoring of the acrosome to the nucleus and a persistence of residual bodies at the level of epididymal sperm midpiece. We identified a quantitative trait locus (QTL) responsible for these phenotypes and we have proposed a short list of candidate genes specifically expressed in spermatids. The future functional validation of candidate genes should allow the identification of new genes and mechanisms involved in male infertility.

[Detection of DPY19L2 gene mutation in 2 cases of globozoospermia]

OBJECTIVE

To investigate the mutation of the DPY19L2 gene in patients with globozoospermia.

METHODS

We collected the clinical data and peripheral blood from 2 patients with globozoospermia and screened for mutation of the DPY19L2 gene by PCR amplification and DNA sequencing technology.

RESULTS

The sperm from the 2 globozoospermia patients were round morphologically under the light microscope, with deeply stained nuclei but no acrosome. Electron microscopy showed the sperm with a large round head but no acrosomal structure, the nuclei enveloped by a single layer of membrane and the cytoplasm dispersed. PCR amplification revealed homozygous deletion of Exon 5, Exon6 and Exon15 in the DPY19L2 gene in both the patients.

CONCLUSIONS

This study proved that the homozygous mutation of DPY19L2 could lead to globozoospermia, which has an important significance for researches on the molecular mechanisms and gene diagnosis of the disease as well as for clinicians in genetic counseling and treatment.

Novel DPY19L2 variants in globozoospermic patients and the overcoming this male infertility

Globozoospermia has been reported to be a rare but severe causation of male infertility, which results from the failure of acrosome biogenesis and sperm head shaping. Variants of dpy-19-like 2 (DPY19L2) are highly related to globozoospermia, but related investigations have been mainly performed in patients from Western countries. Here, we performed a screening of DPY19L2 variants in a cohort of Chinese globozoospermic patients and found that five of nine patients carried DPY19L2 deletions and the other four patients contained novel DPY19L2 point mutations, as revealed by whole-exome sequencing. Patient 3 (P3) contained a heterozygous variant (c.2126+5G>A), P6 contained a homozygous nonsense mutation (c.1720C>T, p.Arg574^*), P8 contained compound heterozygous variants (c.1182-1184delATC, p.Leu394_Ser395delinsPhe; c.368A>T, p.His123Arg), and P9 contained a heterozygous variant (c.1182-1184delATCTT, frameshift). We also reported intracytoplasmic sperm injection (ICSI) outcomes in the related patients, finding that ICSI followed by assisted oocyte activation (AOA) with calcium ionophore achieved high rates of live births. In summary, the infertility of these patients results from DPY19L2 dysfunction and can be treated by ICSI together with AOA.

Proteomic Research of Molecular Defects in Globozoospermia

Globozoospermia is a form of teratozoospermia characterized by round-headed spermatozoa and lack of acrosome. These spermatozoa cannot penetrate the zona pellucida of the oocyte, resulting in unsuccessful fertilization and infertility. When intracytoplasmic sperm injection is performed, the fertilization rate tends to be low. Until now, the causes of this disorder remain to be elucidated; however, mutations of some genes segregating on an autosomal recessive mode have been associated with this infertile condition. DPY19L2 (dpy-19-like 2 [Caenorhabditis elegans]) codes for a transmembrane protein expressed predominantly in spermatids, with specific localization limited to the internal nuclear membrane. Genetic defects in the DPY19L2 gene have been demonstrated the most frequent genetic cause of globozoospermia; however, intracellular molecular pathways related to its encoded protein are largely unknown. In this issue of Proteomics Clinical Applications, Guo and co-workers investigate the proteome of gloobozoospermic spermatozoa. The authors identified 491 proteins that are differentially expressed in globozoospermia (370 are upregulated and 121 are downregulated in DPY19L2-deficient globozoospermic sperm). Notably, the molecular defects identified by the authors are closely related to biological processes involved in acrosome formation, chromatin composition, sperm-egg binding, and fertilization.

Comparison of Human Oocyte Activation Between Round-Headed Sperm Injection Followed by Calcium Ionophore Treatment and Normal Sperm Injection in a Patient With Globozoospermia

Fertilization failure is common in patients with round-headed sperm, a form of globozoospermia. Artificial oocyte activation is able to assist oocyte fertilization after sperm injection in these patients. Comparisons between oocyte fertilization with or without calcium ionophore have been reported in patients with round-headed sperm. However, no comparison has been reported between round-headed sperm injection followed by calcium ionophone activation and normal sperm injection. In this case report, half of oocytes from a patient were injected with her partner's round-headed sperm followed by calcium ionophore activation, and the other half of oocytes were injected with a donor sperm without calcium ionophore activation. The injected oocytes were cultured to examine fertilization, embryo development, and embryonic aneuploidies in the resulting blastocysts. The fertilization rate was lower in round-headed sperm injected oocytes (3/6) than that in donor sperm injected oocytes (5/6), but rates of blastocyst and aneuploidies were similar in the resulting embryos between the two groups. A euploid blastocyst resulted from round-headed sperm injection was transferred, and a healthy baby was delivered. These results indicate that calcium ionophore treatment can assist oocyte activation in patients with round-headed sperm, but its efficiency to activate oocytes is lower than that induced by a normal sperm injection. However, embryo development and chromosome integrity may not be affected by calcium ionophore treatment.

Globozoospermia syndrome: An update

Among the factors involved in male infertility, there is a rare morphology disorder called "globozoospermia" that is classified into total globozoospermia and partial globozoospermia (type I and type II, respectively). This syndrome is primarily characterised by the presence of round-headed spermatozoa with cytoskeleton defects around the nucleus and no acrosome. Current data support the negative correlation between globozoospermia and conventional intracytoplasmic sperm injection (ICSI) outcomes, revealing the need for the management of patients undergoing assisted reproduction technology (ART) through more effective treatment techniques. This review highlights the most important characteristics of globozoospermia such as sperm parameters, DNA/chromatin integrity and sperm DNA fragmentation (SDF), as well as genetic features based on the latest knowledge. Additionally, we looked into current progress on fertilisation potential and possible treatment strategies for patients presenting with globozoospermia.

Mechanism of Acrosome Biogenesis in Mammals

During sexual reproduction, two haploid gametes fuse to form the zygote, and the acrosome is essential to this fusion process (fertilization) in animals. The acrosome is a special kind of organelle with a cap-like structure that covers the anterior portion of the head of the spermatozoon. The acrosome is derived from the Golgi apparatus and contains digestive enzymes. With the progress of our understanding of acrosome biogenesis, a number of models have been proposed to address the origin of the acrosome. The acrosome has been regarded as a lysosome-related organelle, and it has been proposed to have originated from the lysosome or the autolysosome. Our review will provide a brief historical overview and highlight recent findings on acrosome biogenesis in mammals.

Proteomic Analysis of Dpy19l2-Deficient Human Globozoospermia Reveals Multiple Molecular Defects

PURPOSE

To investigate the differences in protein expression between Dpy19l2-deficient human globozoospermia and normozoospermia.

EXPERIMENTAL DESIGN

Human sperm samples from three globozoospermic donors with Dpy19l2 deletion and three normal controls are subjected to TMT quantitative technology. SPESP1, HIST1H4A, and LYZL1 are randomly selected for western blotting analysis. GO annotations are performed using the Database for Annotation, Visualization, and Integrated Discovery.

RESULTS

A total of 2567 proteins are identified, of which 2510 proteins are quantified, and 491 are differentially expressed (fold-change > 2), with 370 upregulated and 121 downregulated in globozoospermic patients. The levels of several important proteins, including SPACA 1, IZUMO1, ZPBP1, and PLCZ1, are decreased in globozoospermic sperm. Bioinformatics analysis indicates the Dpy19l2-deficient sperm presented molecular defects in acrosome, chromatin, sperm-egg interaction, and fertilization.

CONCLUSIONS AND CLINICAL RELEVANCE

The present study is the first to analyze total globozoospermia with Dpy19l2 deletion using high-throughput proteomics. This study may provide insights into the mechanism of globozoospermia.

Comparison of sperm morphology and nuclear sperm quality in SPATA16- and DPY19L2-mutated globozoospermic patients

The aim of this study was to compare the sperm morphology and nuclear sperm quality (sperm aneuploidy and DNA fragmentation) in two groups of globozoospermic patients: DPY19L2-mutated patients (n = 6) and SPATA16-mutated patients (n = 2). Results for these two groups were also compared to a group of fertile men (n = 25). Fluorescence in situ hybridisation was performed for chromosomes X, Y and 18. Sperm DNA fragmentation was evaluated by TUNEL assay. Sanger sequencing was performed for mutations screening of DPY19L2 and SPATA16 genes. Sperm analysis revealed a classic phenotype of total globozoospermia in DPY19L2-mutated group and a particular phenotype characterised by a predominance of double/multiple round-headed (39.00 ± 4.2%) and multi-tailed spermatozoa (26.00 ± 16.97%) in SPATA16-mutated group. FISH analysis showed a significantly higher aneuploidy rate in globozoospermic patients compared to controls (p < 0.05), and a higher rate was observed in SPATA16-mutated group compared to DPY19L2-mutated group (p < 0.05). DNA fragmentation index was significantly higher in globozoospermic men compared to controls (p < 0.001), and there is no statistically significant difference between the two globozoospermic groups. We showed that SPATA16 defects could be associated with an abnormal meiosis leading to a particular morphological sperm defect of double/multiple round-headed and multi-flagella and a higher sperm aneuploidy rate than in case of DPY19L2-defects in classic globozoospermia.

A successful healthy childbirth and an ongoing evolutive pregnancy in a case of partial globozoospermia by hyaluronic acid sperm selection

We here report a successful healthy childbirth and an ongoing evolutive pregnancy in a case of partial globozoospermia after selection of mature spermatozoa bound to hyaluronic acid (HA). The couple underwent two in vitro fertilisation (IVF) cycles. In the first attempt, 14 MII oocytes were retrieved. Randomly, seven oocytes were injected by conventional PVP-ICSI and seven by HA-ICSI. Fertilised oocytes were 2/7 and 4/7 after PVP-ICSI and HA-ICSI respectively. Transfer of two grade A embryos from HA-ICSI lead to birth of a healthy baby. The surplus embryo of the HA-ICSI group was vitrified at blastocyst stage. The two embryos from PVP-ICSI arrested their development. Two years after the childbirth, the vitrified blastocyst was transferred into the uterus, but implant failed. In the second cycle, 14 MII oocytes were retrieved and they were injected by HA-ICSI. Fertilised oocytes were 10 out of 14 injected oocytes. On day 5, two blastocysts were transferred into uterus and a single evolutive pregnancy is ongoing. On day 6, one blastocyst was vitrified. The remaining surplus embryos arrested their development. A healthy childbirth and an ongoing evolutive pregnancy in two consecutive ICSI attempts of the same couple suggest that HA sperm selection might assist in cases with partial globozoospermia.

DNAH6 is a novel candidate gene associated with sperm head anomaly

Globozoospermia and acephalic spermatozoa are two rare sperm head anomalies associated with male infertility. Combination of the two phenotypes in the same patient is extremely rare, so the underlying pathogenesis of this disorder remains unclear. Here, we report a 35-year-old infertile male, who presented with 30% of sperm-lacked heads and 69% of sperm round-headed or small-headed with neck thickening in his ejaculate. Subsequent whole-exome sequencing (WES) analysis identified compound heterozygous variants within the DNAH6 gene. DNAH6 is a testis-specific-expressed protein that was localised to the neck region in the spermatozoa of normal control; however, immunofluorescent staining failed to detect DNAH6 protein in the patient's spermatozoa. Quantitative real-time PCR analysis also showed the complete absence of DNAH6 mRNA in the patient's spermatozoa. Moreover, two cycles of in vitro fertilisation (IVF)-assisted reproduction were carried out, but pregnancy was not achieved after embryo transfer. Therefore, rare sequence variants in DNAH6 might be susceptibility risks for human sperm head anomaly.

Intracytoplasmic Sperm Injection with Assisted Oocyte Activation Resulting in Successful Pregnancies and Live Birth in Couples with Globozoospermia: A Report of Two Cases

Globozoospermia, characterized by round-headed acrosomeless sperm, is a rare and severe form of teratozoospermia. We report a successful pregnancy in two cases of total globozoospermia after intracytoplasmic sperm injection (ICSI) with oocyte activation with calcium ionophore. In thefirst case, globozoospermia was diagnosed on the day of oocyte retrieval. Among 11 retrieved oocytes, only one fertilized after ICSI. The pregnancy test 2 weeks after embryo transfer was negative. Two months later, the patient underwent ovarian stimulation again. The 12 retrieved oocytes were exposed to calcium ionophore medium following ICSI. Four oocytes were fertilized and two blastocysts were transferred resulting in a clinical pregnancy. In the second case, among seven retrieved oocytes, three fertilized after ICSI and assisted oocyte activation, and two 8-cell embryos were transferred, resulting in a positive pregnancy. The successful outcome here justifies the use of ICSI with oocyte activation to improve the pregnancy rate significantly when dealing with globozoospermia.

Association between total globozoospermia and sperm chromatin defects

Globozoospermia is a severe sperm morphological anomaly leading to primary infertility and low fertilisation following intracytoplasmic sperm injection (ICSI). This phenotype is observed in less than 0.1% of infertile men and is determined by small, round-headed spermatozoa with absence of an acrosomal cap, acrosome protease and also cytoskeletal proteins. Failure of oocyte activation is considered as the main cause of fertilisation failure in these individuals post-ICSI. Therefore, artificial oocyte activation (AOA) along with ICSI is commonly implemented. However, based on previous report, fertilisation rate remains low despite implementation of ICSI-AOA. Therefore, other mechanisms like sperm chromatin packaging and DNA fragmentation may account for low fertilisation and development post-ICSI-AOA. Therefore, this study aims to assess and compare the degree of sperm protamine deficiency and DNA fragmentation in large population of infertile men with total globozoospermia (30 globozoospermic men presenting with 100% round-headed spermatozoa) with 22 fertile individuals using chromomycin A3 and TUNEL assay respectively. Results clearly show that mean of sperm concentration and percentage of sperm motility were significantly lower, while percentage of sperm abnormal morphology, protamine-deficient and DNA-fragmented spermatozoa were significantly higher in infertile men with globozoospermia compared to fertile men. Therefore, increased sperm DNA damage in globozoospermia is likely related to defective DNA compaction and antioxidant therapy before ICSI-AOA could be recommended as an appropriate option before ICSI-AOA.

Sperm chromatin quality and DNA integrity in partial versus total globozoospermia

Globozoospermia is a severe form of teratozoospermia with low incidence in infertile patients, considered as one of the important causes of male infertility. The objective was to investigate the chromatin/DNA integrity as well as apoptosis in ejaculated spermatozoa of cases with partial or total globozoospermia. Fifty-seven semen samples were divided into three groups of partial globozoospermia (n = 17), total globozoospermia (n = 10) and normozoospermia (control; n = 30). Sperm chromatin condensation, DNA integrity and apoptosis were assessed using cytochemical assays. The results showed significant differences in sperm parameters of count and motility between two case groups versus controls. The percentages of spermatozoa with abnormal chromatin packaging and protamine deficiency were significantly higher in total and partial globozoospermic men compared to normozoospermic samples. Also, the rates of TUNEL-positive spermatozoa were significantly increased in both globozoospermic cases with respect to the control (18.3 ± 10.1 and 12.3 ± 9.2 versus 5.9 ± 3 respectively). However, no significant differences were noticed between two subgroups of patients with regard to sperm DNA denaturation, DNA fragmentation and apoptosis. Abnormal chromatin packaging, DNA damage and apoptosis were significantly higher in cases than controls. The sperm chromatin/DNA anomalies may be considered as one of the main aetiology of ART failure in globozoospermic patients.

Loss of the Na+/H+ exchanger NHE8 causes male infertility in mice by disrupting acrosome formation

Mammalian sperm feature a specialized secretory organelle on the anterior part of the sperm nucleus, the acrosome, which is essential for male fertility. It is formed by a fusion of Golgi-derived vesicles. We show here that the predominantly Golgi-resident Na⁺/H⁺ exchanger NHE8 localizes to the developing acrosome of spermatids. Similar to wild-type mice, Nhe8^-/- mice generated Golgi-derived vesicles positive for acrosomal markers and attached to nuclei, but these vesicles failed to form large acrosomal granules and the acrosomal cap. Spermatozoa from Nhe8^-/- mice completely lacked acrosomes, were round-headed, exhibited abnormal mitochondrial distribution, and displayed decreased motility, resulting in selective male infertility. Of note, similar features are also found in globozoospermia, one of the causes of male infertility in humans. Germ cell-specific, but not Sertoli cell-specific Nhe8 disruption recapitulated the globozoospermia phenotype, demonstrating that NHE8's role in spermiogenesis is germ cell-intrinsic. Our work has uncovered a crucial role of NHE8 in acrosome biogenesis and suggests that some forms of human globozoospermia might be caused by a loss of function of this Na⁺/H⁺ exchanger. It points to NHE8 as a candidate gene for human globozoospermia and a possible drug target for male contraception.

Genome-wide 5-hydroxymethylcytosine modification pattern is a novel epigenetic feature of globozoospermia

Discovery of 5-hydroxymethylcytosine (5hmC) in mammalian genomes has excited the field of epigenetics, but information on the genome-wide distribution of 5hmC is limited. Globozoospermia is a rare but severe cause of male infertility. To date, the epigenetic mechanism, especially 5hmC profiles involved in globozoospermia progression, remains largely unknown. Here, utilizing the chemical labeling and biotin-enrichment approach followed by Illumina HiSeq sequencing, we showed that (i) 6664, 9029 and 6318 genes contain 5hmC in normal, abnormal, and globozoospermia sperm, respectively; (ii) some 5hmC-containing genes significantly involves in spermatogenesis, sperm motility and morphology, and gamete generation; (iii) 5hmC is exclusively localized in sperm intron; (iv) approximately 40% imprinted genes have 5hmC modification in sperm genomes, but globozoospermia sperm exhibiting a large portion of imprinted genes lose the 5hmC modification; (v) six imprinted genes showed different 5hmC patterns in abnormal sperm (GDAP1L1, GNAS, KCNK9, LIN28B, RB1, RTL1), and five imprinted genes showed different 5hmC patterns in globozoospermia sperm (KCNK9, LIN28B, RB1, SLC22A18, ZDBF2). These results suggested that differences in genome-wide 5hmC patterns may in part be responsible for the sperm phenotype. All of this may improve our understanding of the basic molecular mechanism underlying sperm biology and the etiology of male infertility.

Identification of a new DPY19L2 mutation and a better definition of DPY19L2 deletion breakpoints leading to globozoospermia

STUDY HYPOTHESIS

The purpose of this study was to analyze DPY19L2 sequence variants to investigate the mechanism leading to the entire DPY19L2 deletion in a large cohort of infertile globozoospermic patients.

STUDY FINDING

An improved analysis of the DPY19L2 deletion breakpoints (BPs) allowed us to identify two BPs located in a small 1 kb region and to more precisely localize the BPs reported previously.

WHAT IS KNOWN ALREADY

Three genes [spermatogenesis associated 16 (SPATA16), protein interacting with PRKCA (PICK1) and DPY19L2] were previously correlated with globozoospermia, but a homozygous deletion of the entire DPY19L2 was identified as the most frequent alteration causing this phenotype. In addition, several point mutations in this gene were reported. In previous work, we have identified nine BPs for the DPY19L2 deletion clustered in two hotspot regions, while others reported a total of five BPs.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

We screened for the DPY19L2 deletion and for mutations in the DPY19L2, SPATA16 and PICK1 genes in a cohort of 21 Tunisian globozoospermic patients. In order to characterize the DPY19L2 deletion BPs, we sequenced a 2 kb fragment on low copy repeat (LCR) 1 and LCR2 in Tunisian fertile controls to distinguish between single-nucleotide polymorphisms (SNPs) and LCR-specific markers.

MAIN RESULTS AND THE ROLE OF CHANCE

Molecular analyses performed on 18 genetically independent individuals showed that 11 (61.1%) were homozygous for the DPY19L2 deletion, 2 (11.1%) were homozygous for the non-synonymous mutation (p.R298C) in exon 8, 1 patient (5.6%) was homozygous for a new splice-site mutation at the junction exon-intron 16 [c.1579_1580+4delAGGTAAinsTCAT] and no DPY19L2, SPATA16 or PICK1 mutations were identified for 4 patients (22.2%). By defining 15 specific LCR markers, we characterized 2 BPs for the DPY19L2 deletion in 11 patients showing the homozygous deletion. Using 20 non-LCR-specific SNPs, we identified 8 distinct haplotypes.

LIMITATIONS, REASONS FOR CAUTION

A limitation of this study is the small number of patients owing to the rarity of this form of male infertility.

WIDER IMPLICATIONS OF THE FINDINGS

Our data showed that some nucleotides, described by others as LCR-specific markers and used to limit their BPs, were in fact SNPs demonstrating the difficulty in precisely determining the localization of BPs.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by the French Centre National de la Recherche Scientifique (CNRS), Institut National de la Santé et de la Recherche Médicale (INSERM), the Ministère de l'Education Nationale et de l'Enseignement Supérieur et de la Recherche, the University of Strasbourg, the University Hospital of Strasbourg, the Agence Nationale pour la Recherche, the Agence de la BioMédecine and l'Agence Universitaire de la Francophonie (AUF). There are no conflicts of interest to declare.

Subcellular localization of phospholipase Cζ in human sperm and its absence in DPY19L2-deficient sperm are consistent with its role in oocyte activation

We recently identified the DPY19L2 gene as the main genetic cause of human globozoospermia (70%) and described that Dpy19l2 knockout (KO) mice faithfully reproduce the human phenotype of globozoospermia making it an excellent model to characterize the molecular physiopathology of globozoospermia. Recent case studies on non-genetically characterized men with globozoospermia showed that phospholipase C, zeta (PLCζ), the sperm factor thought to induce the Ca(2+) oscillations at fertilization, was absent from their sperm, explaining the poor fertilization potential of these spermatozoa. Since 30% of globozoospermic men remain genetically uncharacterized, the absence of PLCζ in DPY19L2 globozoospermic men remains to be formally established. Moreover, the precise localization of PLCζ and the reasons underlying its loss during spermatogenesis in globozoospermic patients are still not understood. Herein, we show that PLCζ is absent, or its presence highly reduced, in human and mouse sperm with DPY19L2-associated globozoospermia. As a consequence, fertilization with sperm from Dpy19l2 KO mice failed to initiate Ca(2+) oscillations and injected oocytes remained arrested at the metaphase II stage, although a few human oocytes injected with DPY19L2-defective sperm showed formation of 2-pronuclei embryos. We report for the first time the subcellular localization of PLCζ in control human sperm, which is along the inner acrosomal membrane and in the perinuclear theca, in the area corresponding to the equatorial region. Because these cellular components are absent in globozoospermic sperm, the loss of PLCζ in globozoospermic sperm is thus consistent and reinforces the role of PLCζ as an oocyte activation factor necessary for oocyte activation. In our companion article, we showed that chromatin compaction during spermiogenesis in Dpy19l2 KO mouse is defective and leads to sperm DNA damage. Together, these defects explain the poor fertilization potential of DPY19L2-globozoospermic sperm and the compromised developmental potential of embryos obtained using sperm from patients with a deletion of the DPY19L2 gene.

Dpy19l2-deficient globozoospermic sperm display altered genome packaging and DNA damage that compromises the initiation of embryo development

We recently identified the DPY19L2 gene as the main genetic cause of human globozoospermia. Non-genetically characterized cases of globozoospermia were associated with DNA alterations, suggesting that DPY19L2-dependent globozoospermia may be associated with poor DNA quality. However the origins of such defects have not yet been characterized and the consequences on the quality of embryos generated with globozoospermic sperm remain to be determined. Using the mouse model lacking Dpy19l2, we compared several key steps of nuclear compaction. We show that the kinetics of appearance and disappearance of the histone H4 acetylation waves and of transition proteins are defective. More importantly, the nuclear invasion by protamines does not occur. As a consequence, we showed that globozoospermic sperm presented with poor sperm chromatin compaction and sperm DNA integrity breakdown. We next assessed the developmental consequences of using such faulty sperm by performing ICSI. We showed in the companion article that oocyte activation (OA) with globozoospermic sperm is very poor and due to the absence of phospholipase Cζ; therefore artificial OA (AOA) was used to bypass defective OA. Herein, we evaluated the developmental potential of embryos generated by ICSI + AOA in mice. We demonstrate that although OA was fully rescued, preimplantation development was impaired when using globozoospermic sperm. In human, a small number of embryos could be generated with sperm from DPY19L2-deleted patients in the absence of AOA and these embryos also showed a poor developmental potential. In conclusion, we show that chromatin compaction during spermiogenesis in Dpy19l2 KO mouse is defective and leads to sperm DNA damage. Most of the DNA breaks were already present when the sperm reached the epididymis, indicating that they occurred inside the testis. This result thus suggests that testicular sperm extraction in Dpy19l2-dependent globozoospermia is not recommended. These defects may largely explain the poor embryonic development of most mouse and human embryos obtained with globozoospermic sperm.

Total globozoospermia associated with increased frequency of immature spermatozoa with chromatin defects and aneuploidy: a case report

Globozoospermia, characterised by the presence of round spermatozoa lacking acrosomes in an ejaculate, is a known cause of male infertility. Semen analysis, including sperm chromatin structure assay, toluidine blue, chromomycin A3 and aniline blue staining and fluorescence in situ hybridisation, was performed in an infertile globozoospermic patient to establish to which extent these genetic factors contributed to his infertility. No spermatozoa capable of hyaluronan (HA) binding were detected in the HA binding assay. Increased rates of immature spermatozoa with defective replacement of histones by protamines, DNA breaks and disturbed chromatin integrity and sperm aneuploid for the sex chromosomes were observed. Intracytoplasmic sperm injection (ICSI) was used in three in vitro fertilisation (IVF) cycles, and enough morphologically well-developing embryos were obtained in each cycle. However, no pregnancy was achieved. The infertility of our couple, resistant to IVF/ICSI treatment, was most probably caused by a combination of male and female factors.