Dynamic of contribution of UBPy-sorted cargo to acrosome biogenesis: effects of its derailment in a mouse model of globozoospermia, the infertile Vps54 (L967Q) mutant

Novel HYDIN variants associated with male infertility in two Chinese families

INTRODUCTION

Infertility is a major disease affecting human life and health, among which male factors account for about half. Asthenoteratozoospermia accounts for the majority of male infertility. High-throughput sequencing techniques have identified numerous variants in genes responsible for asthenoteratozoospermia; however, its etiology still needs to be studied.

METHOD

In this study, we performed whole-exome sequencing on samples from 375 patients with asthenoteratozoospermia and identified two HYDIN compound heterozygous variants, a primary ciliary dyskinesia (PCD)-associated gene, in two unrelated subjects. H&E staining, SEM were employed to analyze the varies on sperm of patients, further, TEM was employed to determine the ultrastructure defects. And westernblot and immunostaining were chose to evaluate the variation of structural protein. ICSI was applied to assist the mutational patient to achieve offspring.

RESULT

We identified two HYDIN compound heterozygous variants. Patient AY078 had novel compound heterozygous splice variants (c.5969-2A>G, c.6316+1G>A), altering the consensus splice acceptor site of HYDIN. He was diagnosed with male infertility and PCD, presenting with decreased sperm progressive motility and morphological abnormalities, and bronchial dilatation in the inferior lobe. Compared to the fertile control, HYDIN levels, acrosome and centrosome markers (ACTL7A, ACROSIN, PLCζ1, and Centrin1), and flagella components (TOMM20, SEPT4, SPEF2, SPAG6, and RSPHs) were significantly reduced in HYDIN-deficient patients. Using intracytoplasmic sperm injection (ICSI), the patient successfully achieved clinical pregnancy. AY079 had deleterious compound heterozygous missense variants, c.9507C>G (p. Asn3169Lys) and c.14081G>A (p. Arg4694His), presenting with infertility; however, semen samples and PCD examination were unavailable.

DISCUSSION

Our findings provide the first evidence that the loss of HYDIN function causes asthenoteratozoospermia presenting with various defects in the flagella structure and the disassembly of the acrosome and neck. Additionally, ICSI could rescue this failure of insemination caused by immobile and malformed sperm induced by HYDIN deficiency.

KATNB1 is a master regulator of multiple katanin enzymes in male meiosis and haploid germ cell development

Katanin microtubule-severing enzymes are crucial executers of microtubule regulation. Here, we have created an allelic loss-of-function series of the katanin regulatory B-subunit KATNB1 in mice. We reveal that KATNB1 is the master regulator of all katanin enzymatic A-subunits during mammalian spermatogenesis, wherein it is required to maintain katanin A-subunit abundance. Our data shows that complete loss of KATNB1 from germ cells is incompatible with sperm production, and we reveal multiple new spermatogenesis functions for KATNB1, including essential roles in male meiosis, acrosome formation, sperm tail assembly, regulation of both the Sertoli and germ cell cytoskeletons during sperm nuclear remodelling, and maintenance of seminiferous epithelium integrity. Collectively, our findings reveal that katanins are able to differentially regulate almost all key microtubule-based structures during mammalian male germ cell development, through the complexing of one master controller, KATNB1, with a 'toolbox' of neofunctionalised katanin A-subunits.

Whole-exome sequencing of a cohort of infertile men reveals novel causative genes in teratozoospermia that are chiefly related to sperm head defects

STUDY QUESTION

Can whole-exome sequencing (WES) and in vitro validation studies identify new causative genes associated with teratozoospermia, particularly for sperm head defect?

SUMMARY ANSWER

We investigated a core group of infertile patients, including 82 cases with unexplained abnormal sperm head and 67 individuals with multiple morphological abnormalities of the sperm flagella (MMAF), and revealed rare and novel deleterious gene variants correlated with morphological abnormalities of the sperm head or tail defects.

WHAT IS KNOWN ALREADY

Teratozoospermia is one of the most common factors causing male infertility. Owing to high phenotypic variability, currently known genetic causes of teratozoospermia can only explain a rather minor component for patients with anomalous sperm-head shapes, and the agents responsible for atypical sperm head shapes remain largely unknown.

STUDY DESIGN, SIZE, DURATION

We executed WES analysis of a Chinese cohort of patients (N = 149) with teratozoospermia to identify novel genetic causes particularly for defective sperm head. We also sought to reveal the influence of different abnormalities of sperm morphology on ICSI outcome.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In this study, a cohort of 149 infertile men (82 with abnormal sperm head and 67 with MMAF) were recruited. We implemented WES on infertile patients and analyzed the negative effects of the mutations of candidate genes on their protein conformations and/or expression. We also investigated the candidate genes' spatiotemporal expression/localization during spermatogenesis in both humans and mice, and explored their interactions with proteins that are known to be involved in sperm development. We also compared the ICSI outcomes of the affected individuals with various aberrations in sperm morphology.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified rare and deleterious variants of piwi like RNA-mediated gene silencing 4 (PIWIL4: 1/82 patients, 1.21%), coiled-coil and C2 domain containing 1B (CC2D1B: 1/82 patients, 1.21%), cyclin B3 (CCNB3: 1/82 patients, 1.21%), KIAA1210 (KIAA1210: 2/82 patients, 2.43%) and choline phosphotransferase 1 (CHPT1: 1/82 patients, 1.21%), which are novel correlates of morphological abnormalities of the sperm head; functional evidence supports roles for all of these genes in sperm head formation. The mutations of septin 12 (SEPTIN12: 2/82 patients, 2.43%) are suggested to be associated with acrosome defects. We additionally observed novel causative mutations of dynein axonemal heavy chain 2 (DNAH2: 1/67 patients, 1.49%), dynein axonemal heavy chain 10 (DNAH10: 1/67 patients, 1.49%) and dynein axonemal heavy chain 12 (DNAH12: 1/67 patients, 1.49%) in patients with MMAF, and revealed a significantly lower fertilization rate of the abnormal sperm-head group compared to the MMAF group following ICSI. Consequently, our study also suggests that the mutations of PIWIL4 and CC2D1B might be circumvented by ICSI to a degree, and that CHPT1 and KIAA1210 loss-of-function variants might be associated with failed ICSI treatment.

LIMITATIONS, REASONS FOR CAUTION

In this study, we discovered the relationship between the genotype and phenotype of the novel causative genes of sperm head deformities in humans. However, the molecular mechanism of the relevant genes involved in sperm head development needs to be further illuminated in future research. Furthermore, evidence should be provided using knockout/knock-in mouse models for additional confirmation of the roles of these novel genes in spermatogenesis.

WIDER IMPLICATIONS OF THE FINDINGS

This cohort study of 149 Chinese infertile men documents novel genetic factors involved in teratozoospermia, particularly in anomalous sperm head formation. For the first time, we suggest that SEPTIN12 is related to human acrosomal hypoplasia, and that CCNB3 is a novel causative gene for globozoospermia in humans. We also uncovered variants in two genes-KIAA1210 and CHPT1associated with acrosomal biogenesis in patients with small or absent acrosomes. Additionally, it is postulated that loss-of-function mutations of PIWIL4 and CC2D1B have a contribution to the abnormal sperm-head formation. Furthermore, we are first to demonstrate the influence of different sperm morphologies on ICSI outcomes and indicates that the abnormal sperm head may play a significant role in fertilization failure. Our findings therefore provide valuable information for the diagnosis of teratozoospermia, particularly with respect to abnormalities of the sperm head. This will allow clinicians to adopt the optimal treatment strategy and to develop personalized medicine directly targeting these effects.

STUDY FUNDING/COMPETING INTEREST(S)

This work was financed by the West China Second University Hospital of Sichuan University (KS369 and KL042). The authors declare that they do not have any conflicts of interests.

TRIAL REGISTRATION NUMBER

N/A.

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

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

Neuroprotective Effects of Testosterone in Male Wobbler Mouse, a Model of Amyotrophic Lateral Sclerosis

Patients suffering of amyotrophic lateral sclerosis (ALS) present motoneuron degeneration leading to muscle atrophy, dysphagia, and dysarthria. The Wobbler mouse, an animal model of ALS, shows a selective loss of motoneurons, astrocytosis, and microgliosis in the spinal cord. The incidence of ALS is greater in men; however, it increases in women after menopause, suggesting a role of sex steroids in ALS. Testosterone is a complex steroid that exerts its effects directly via androgen (AR) or Sigma-1 receptors and indirectly via estrogen receptors (ER) after aromatization into estradiol. Its reduced-metabolite 5α-dihydrotestosterone acts via AR. This study analyzed the effects of testosterone in male symptomatic Wobblers. Controls or Wobblers received empty or testosterone-filled silastic tubes for 2 months. The cervical spinal cord from testosterone-treated Wobblers showed (1) similar androgen levels to untreated control and (2) increased levels of testosterone, and its 5α-reduced metabolites, 5α- dihydrotestosterone, and 3β-androstanediol, but (3) undetectable levels of estradiol compared to untreated Wobblers. Testosterone-treated controls showed comparable steroid concentrations to its untreated counterpart. In testosterone- treated Wobblers a reduction of AR, ERα, and aromatase and high levels of Sigma-1 receptor mRNAs was demonstrated. Testosterone treatment increased ChAT immunoreactivity and the antiinflammatory mediator TGFβ, while it lessened vacuolated motoneurons, GFAP+ astrogliosis, the density of IBA1+ microgliosis, proinflammatory mediators, and oxidative/nitrosative stress. Clinically, testosterone treatment in Wobblers slowed the progression of paw atrophy and improved rotarod performance. Collectively, our findings indicate an antiinflammatory and protective effect of testosterone in the degenerating spinal cord. These results coincided with a high concentration of androgen-reduced derivatives after testosterone treatment suggesting that the steroid profile may have a beneficial role on disease progression.

Destruction or Reconstruction: A Subtle Liaison between the Proteolytic and Signaling Role of Protein Ubiquitination in Spermatogenesis

Ubiquitination is one of the most diverse forms of protein post-translational modification that changes the function of the landscape of substrate proteins in response to stimuli, without the need for "de novo" protein synthesis. Ubiquitination is involved in almost all aspects of eukaryotic cell biology, from the best-studied role in promoting the removal of faulty or unnecessary proteins by the way of the ubiquitin proteasome system and autophagy-lysosome pathway to the recruitment of proteins in specific non-proteolytic signaling pathways, as emerged by the more recent discoveries about the protein signature with peculiar types of ubiquitin chains. Spermatogenesis, on its own, is a complex cellular developmental process in which mitosis, meiosis, and cell differentiation coexist so to result in the continuous formation of haploid spermatozoa. Successful spermatogenesis is thus at the same time a mixed result of the precise expression and correct intracellular destination of structural proteins and enzymes, from one hand, and the fine removal by targeted degradation of unfolded or damaged proteins as well as of obsolete, outlived proteins, from the other hand. In this minireview, I will focus on the importance of the ubiquitin system all over the spermatogenic process, discussing both proteolytic and non-proteolytic functions of protein ubiquitination. Alterations in the ubiquitin system have been in fact implicated in pathologies leading to male infertility. Notwithstanding several aspects of the multifaceted world of the ubiquitin system have been clarified, the physiological meaning of the so-called ubiquitin code remains still partially elusive. The studies reviewed in this chapter provide information that could aid the investigators to pursue new promising discoveries in the understanding of human and animal reproductive potential.

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

BACKGROUND

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

OBJECTIVE AND RATIONALE

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

SEARCH METHODS

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

OUTCOMES

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

WILDER IMPLICATIONS

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

Chronic arsenic exposure lowered sperm motility via impairing ultra-microstructure and key proteins expressions of sperm acrosome and flagellum formation during spermiogenesis in male mice

Arsenic (As) poisoning and its potential reproductive functional lesions are a global environmental concern. Recent studies shown that spermiogenesis tends to be a major target process in arsenic-induced male infertility, however, the underlying mechanisms are not fully illuminated. In the present study, 32 fertility related indices including sperm motility, dynamic acrosome formation and sperm flagellum during spermiogenesis in testes were evaluated in adult male mice treated with 0, 0.2, 2, and 20 ppm As₂O₃ via drinking water for 180 consecutive days. The results showed that out of 32 indices, 11, 25, and 29 indicators were changed statistically by 0.2-, 2-, and 20- ppm As₂O₃ treatment compared to the controls (0 ppm As₂O₃), respectively, which reveals a significant dose-dependent relationship. For details, sperm motilities were significantly decreased by 18.85%, 32.47% and 29.53% in three As₂O₃ treatment groups compared to the control group. Meanwhile, the ultra-structures of acrosome formation and sperm flagellum in testes have been altered by chronic arsenic exposure. Furthermore, arsenic decreased the mRNA expressions of 11 out of 13 genes associated with acrosome biosynthesis and 11 out of 12 genes related to flagellum formation in testes, particularly, down-regulated DPY19L2, AKAP3, AKAP4, CFAP44 and SPAG16 were further confirmed at the protein levels by western blotting. Taken together, chronic arsenic exposure declines male fertility by disorganizing dynamic acrosome and flagellum formation in testes. Especially, DPY19L2, AKAP3, AKAP4, CFAP44, and SPAG16 maybe the potential targets in this process. These results may offer not only a new insight to the mechanism of arsenic-induced male reproductive toxicity, but also provide a clue for the diagnosis and therapy of arseniasis.

Ubiquitin-specific protease 8 (USP8/UBPy): a prototypic multidomain deubiquitinating enzyme with pleiotropic functions

Protein modification by ubiquitin is one of the most versatile posttranslational regulations and counteracted by almost 100 deubiquitinating enzymes (DUBs). USP8 was originally identified as a growth regulated ubiquitin-specific protease and is like many other DUBs characterized by its multidomain architecture. Besides the catalytic domain, specific protein-protein interaction modules were characterized which contribute to USP8 substrate recruitment, regulation and targeting to distinct protein complexes. Studies in mice and humans impressively showed the physiological relevance and non-redundant function of USP8 within the context of the whole organism. USP8 knockout (KO) mice exhibit early embryonic lethality while induced deletion in adult animals rapidly causes lethal liver failure. Furthermore, T-cell specific ablation disturbs T-cell development and function resulting in fatal autoimmune inflammatory bowel disease. In human patients, somatic mutations in USP8 were identified as the underlying cause of adrenocorticotropic hormone (ACTH) releasing pituitary adenomas causing Cushing's disease (CD). Here we provide an overview of the versatile molecular, cellular and pathology associated function and regulation of USP8 which appears to depend on specific protein binding partners, substrates and the cellular context.

Vps13b is required for acrosome biogenesis through functions in Golgi dynamic and membrane trafficking

The sperm acrosome is a lysosome-related organelle that develops using membrane trafficking from the Golgi apparatus as well as the endolysosomal compartment. How vesicular trafficking is regulated in spermatids to form the acrosome remains to be elucidated. VPS13B, a RAB6-interactor, was recently shown involved in endomembrane trafficking. Here, we report the generation of the first Vps13b-knockout mouse model and show that male mutant mice are infertile due to oligoasthenoteratozoospermia. This phenotype was explained by a failure of Vps13b deficient spermatids to form an acrosome. In wild-type spermatids, immunostaining of Vps13b and Rab6 revealed that they transiently locate to the acrosomal inner membrane. Spermatids lacking Vps13b did not present with the Golgi structure that characterizes wild-type spermatids and showed abnormal targeting of PNA- and Rab6-positive Golgi-derived vesicles to Eea1- and Lamp2-positive structures. Altogether, our results uncover a function of Vps13b in the regulation of the vesicular transport between Golgi apparatus, acrosome, and endolysosome.

AU040320 deficiency leads to disruption of acrosome biogenesis and infertility in homozygous mutant mice

Study of knockout (KO) mice has helped understand the link between many genes/proteins and human diseases. Identification of infertile KO mice provides valuable tools to characterize the molecular mechanisms underlying gamete formation. The KIAA0319L gene has been described to have a putative association with dyslexia; surprisingly, we observed that homozygous KO males for AU040320, KIAA0319L ortholog, are infertile and present a globozoospermia-like phenotype. Mutant spermatozoa are mostly immotile and display a malformed roundish head with no acrosome. In round spermatids, proacrosomal vesicles accumulate close to the acroplaxome but fail to coalesce into a single acrosomal vesicle. In wild-type mice AU040320 localises to the trans-Golgi-Network of germ cells but cannot be detected in mature acrosomes. Our results suggest AU040320 may be necessary for the normal formation of proacrosomal vesicles or the recruitment of cargo proteins required for downstream events leading to acrosomal fusion. Mutations in KIAA0319L could lead to human infertility; we screened for KIAA0319L mutations in a selected cohort of globozoospermia patients in which no genetic abnormalities have been previously identified, but detected no pathogenic changes in this particular cohort.