The Sept4 septin locus is required for sperm terminal differentiation in mice

Effect of 16h of rabbit sperm incubation on capacitation and heterologous in vitro fertilization

In vitro fertilization (IVF) in rabbits is an important biotechnology, but its success remains low due to inefficient sperm capacitation. This study examines relationships between motility parameters (MP), protein tyrosine phosphorylation (PTP) and acrosomal exocytosis (AE) between sperm recovered after direct swim-up (DSU), and after 16 h of in vitro incubation under capacitating conditions, and heterologous IVF capacity. Variables were assessed in fresh ejaculates (ES), and after 2 h of DSU, and 16 h (T16) of incubation. PTP were grouped into four patterns in the different sperm structures according to their time-dependent appearance and AE. Throughout incubation, MP remained stable whereas AE increased after DSU and 16 h of incubation. Mid-piece PTP patterns increased after DSU and persisted until 16 h in reacted (R) and non-reacted spermatozoa (NR). In R and NR, annulus-ring PTP levels were also significantly higher in T16 versus DSU or ES. Flagellum PTP levels rose significantly during incubation such that highest levels were recorded in T16. In R sperm, levels of PTP patterns associated with the equatorial zone in T16 were significantly higher compared to NR and to DSU and ES. Cleavage rates were significantly higher at T16 than DSU and these were similar to rates recorded for homologous IVF used as positive control. Our capacitation protocol and PTP patterns at 16 h rendered the sperm competent to fertilize an oocyte in vitro. This time point matches the physiological timing of fertilization in vivo. We also describe a new annulus ring PTP pattern for this species.

Septins in animal tissue architecture: more than just peanuts

Septins are cytoskeletal guanosine triphosphate (GTP)-binding proteins that were discovered in budding yeast and are conserved from algae and protists to mammals. Septins assemble into heteromeric complexes, which can polymerize into filaments and higher-order filament architectures, and perform functions in a wide range of biological processes, including cell division and motility and tissue morphogenesis. Although septin dysfunction in animals is linked to infertility, defective organogenesis, neurodegenerative diseases, and cancer, the molecular mechanisms underlying septin function are not clear. Studies of septins in vivo in whole animals provide a powerful approach for gaining insights into the role of septins in animal pathophysiology and unraveling the molecular and cell biological basis of septin function.

UBL7 is indispensable for spermiogenesis through protecting critical factors from excessive degradation by proteasomes

Spermiogenesis is a tightly regulated process to produce mature sperm cells. The ubiquitin-proteasome system (UPS) plays a crucial role in controlling protein half-life and is essential for spermiogenesis. Recently, proteins containing ubiquitin-like domains and ubiquitin-associated domains (UBL-UBA proteins) have emerged as novel regulators within the UPS. In this study, we demonstrate that UBL7, a testis-enriched UBL-UBA protein, is indispensable for sperm formation. Deficiency of UBL7 leads to severe malformations of both the sperm tail and head. Mechanistically, UBL7 interacts with the valosin-containing protein (VCP) complex and proteasomes, and shuttles substrates between them. Notably, UBL7 slows down the degradation rates of substrates involved in endoplasmic reticulum-associated degradation (ERAD) within cells. Through a two-step immunoprecipitation method, we identify several essential factors in spermatids that are protected by UBL7, including factors involved in the development of manchette (such as IFT140), head-tail coupling apparatus (such as SPATA20) and cytoplasmic droplets (such as HK1 and SLC2a3). In summary, our findings highlight UBL7 as a guardian that protects crucial factors from excessive degradation and thereby ensures successful spermiogenesis.

SEPT14 complexes maintain sperm morphogenesis and function

Mutations in the septin (SEPT) family lead to male infertility. Septin 14 (SEPT14) is abundantly expressed in the testis, and its expression is significantly reduced in individuals with teratozoospermia, suggesting that SEPT14 may play a role in spermatogenesis. Here, we demonstrated that Sept14 is expressed mainly at the acroplaxome, manchette, neck, and annulus during spermiogenesis. To study the role of SEPT14 in sperm morphogenesis and function, the Sept14 knockout (Sept14-/-) mice were generated. The Sept14-/- male mice were subfertile and presented phenotypes such as irregular acrosomes, DNA damage, disorganized mitochondria, and displaced annuli. These abnormalities contributed to reduced sperm motility and impaired capacitation. Mechanistically, in the sperm head, SEPT14 interacted and colocalized with microtubules and actin during the manchette formation at the sperm metamorphosis phase. In the annulus, SEPT14 interacted with SEPT9, SEPT7, and SEPT2 to form the septin filaments to maintain the localization of the annulus. The GTP-binding domain (GBD) of SEPT14 interacted with the GBD of SEPT2, whereas the C-terminus of SEPT14 interacted with the GBD of SEPT7. Thus, our study reveals a role of SEPT14 in mediating sperm morphogenesis.

Human asthenozoospermia: Update on genetic causes, patient management, and clinical strategies

BACKGROUND

In mammals, sperm fertilization potential relies on efficient progression within the female genital tract to reach and fertilize the oocyte. This fundamental property is supported by the flagellum, an evolutionarily conserved organelle, which contains dynein motor proteins that provide the mechanical force for sperm propulsion and motility. Primary motility of the sperm cells is acquired during their transit through the epididymis and hyperactivated motility is acquired throughout the journey in the female genital tract by a process called capacitation. These activation processes rely on the micro-environment of the genital tracts. In particular, during capacitation, a panoply of ion transporters located at the surface of the sperm cells mediate complex ion exchanges, which induce an increase in plasma membrane fluidity, the alkalinization of the cytoplasm and protein phosphorylation cascades that are compulsory for sperm hyperactivation and fertilization potential. As a consequence, both structural and functional defects of the sperm flagellum can affect sperm motility, resulting in asthenozoospermia, which constitutes the most predominant pathological condition associated with human male infertility.

OBJECTIVES

Herein, we have performed a literature review to provide a comprehensive description of the recent advances in the genetics of human asthenozoospermia.

RESULTS AND DISCUSSION

We describe the currently knowledge on gene mutations that affect sperm morphology and motility, namely, asthenoteratozoospermia; we also specify the gene mutations that exclusively affect sperm function and activation, resulting in functional asthenozoospermia. We discuss the benefit of this knowledge for patient and couple management, in terms of genetic counselling and diagnosis of male infertility as a sole phenotype or in association with ciliary defects. Last, we discuss the current strategies that have been initiated for the development of potential therapeutical and contraceptive strategies targeting genes that are essential for sperm function and activation.

The annulus: composition, role and importance in sperm flagellum biogenesis and male fertility

The annulus is an electron-dense ring structure that surrounds the axoneme and compartmentalizes the sperm flagellum into two parts: the midpiece and the principal piece. The function of the annulus as a diffusion barrier in the mature spermatozoon is now well described but its function during spermiogenesis remains unclear. The intriguing spatio-temporal dynamics of the annulus during spermiogenesis and its position at the interface of the two main flagellar compartments have been highlighted for more than 50 years, and suggest a major role in this process. During the last decade, numerous studies contributed in establishing a repertoire of proteins known to be located at the annulus. Mutant mouse models of invalidation of these proteins have provided essential information and clues for novel hypotheses regarding the functions and regulation of this structure. Importantly, the recent identification in humans of homozygous mutations of genes coding for annulus proteins and leading to sterility have reinforced the importance of this ring structure for sperm physiology and male fertility. This review provides a comprehensive description of all the knowledge obtained in the last several years regarding the annulus composition and functions, both in mice and in humans.

TMEM232 is required for the formation of sperm flagellum and male fertility in mice

Asthenoteratozoospermia is a major cause of male infertility. Thus far, the identified related genes can explain only a small share of asthenoteratozoospermia cases, suggesting the involvement of other genes. The transmembrane protein TMEM232 is highly expressed in mouse testes. In the present study, to determine its function of TMEM232 in testes, we constructed a Tmem232-null mouse model using CRISPR-Cas9 technology. Tmem232 knockout (KO) male mice was completely infertile, and their sperm were immotile, with morphological defects of the flagellum. Electron microscopy revealed an aberrant midpiece-principal junction and the loss of the fourth outer microtubule doublet in the sperm of Tmem232-/- mice. Sperm cells presented an 8 + 2 conformation and an irregular arrangement of the mitochondrial sheath. Proteomic analysis revealed altered expression of proteins related to flagellar motility, sperm capacitation, the integrity and stability of sperm structure, especially an upregulated expression of multiple ribosome components in TMEM232-deficient spermatids. Additionally, TMEM232 was observed to be involved in autophagy by interacting with autophagy-related proteins, such as ATG14, to regulate ribosome homeostasis during spermiogenesis. These results suggest that TMEM232, as a potential scaffold protein involving in the correct assembly, distribution, and stability maintenance of certain functional complexes by recruiting key intracellular proteins, is essential for the formation of a highly structured flagellum and plays an important role in the autophagic elimination of cytosolic ribosomes to provide energy for sperm motility.

CABS1 Is Essential for Progressive Motility and the Integrity of Fibrous Sheath in Mouse Epididymal Spermatozoa

The calcium-binding protein spermatid-associated 1 (CABS1) localizes to the principal piece of mature sperm flagella. Deletion of CABS1 results in subfertility in male mice, possibly due to an impaired annulus in the sperm flagella. However, it is unknown whether there are other mechanisms by which CABS1 affects male fertility. Our current investigation has uncovered that CABS1 is located in the midsection of the flagellum in testicular sperm and the principal piece in epididymal sperm. Moreover, male mice lacking CABS1 exhibit a defect in the progressive motility of sperm. Furthermore, the regulation of calcium levels, which has been reported to have a significant impact on sperm motility, capacitation, and the acrosome reaction, is also affected when sperm are exposed to alkalized high-salt buffer (pH 8.0) and progesterone (100 μM) in Cabs1-null spermatozoa. This alteration in calcium response may contribute to changes in the phosphorylation of PKA substrates and subsequent phosphorylation of tyrosine residues. Additionally, the absence of CABS1 leads to a defective fibrous sheath and abnormal configuration of doublet microtubules in post-testicular sperm. These findings indicate that the absence of CABS1 also disrupts the structural integrity of the fibrous sheath, resulting in male subfertility. The highly conserved nature of CABS1 in humans suggests that it could potentially be a contributing factor to asthenozoospermia in men.

Septins as key players in spermatogenesis, fertilisation and pre-implantation embryogenic cytoplasmic dynamics

Septins are a family of cytokinesis-related proteins involved in regulating cytoskeletal design, cell morphology, and tissue morphogenesis. Apart from cytokinesis, as a fourth component of cytoskeleton, septins aid in forming scaffolds, vesicle sorting and membrane stability. They are also known to be involved in the regulation of intracellular calcium (Ca2+) via the STIM/Orai complex. Infertility affects ~ 15% of couples globally, while male infertility affects ~ 7% of men. Global pregnancy and live birth rates following fertility treatment remain relatively low, while there has been an observable decline in male fertility parameters over the past 60 years. Low fertility treatment success can be attributed to poor embryonic development, poor sperm parameters and fertilisation defects. While studies from the past few years have provided evidence for the role of septins in fertility related processes, the functional role of septins and its related complexes in cellular processes such as oocyte activation, fertilization, and sperm maturation are not completely understood. This review summarizes the available knowledge on the role of septins in spermatogenesis and oocyte activation via Ca2+ regulation, and cytoskeletal dynamics throughout pre-implantation embryonic development. We aim to identify the currently less known mechanisms by which septins regulate these immensely important mechanisms with a view of identifying areas of investigation that would benefit our understanding of cell and reproductive biology, but also provide potential avenues to improve current methods of fertility treatment.

The Molecular Basis of Multiple Morphological Abnormalities of Sperm Flagella and Its Impact on Clinical Practice

Multiple morphological abnormalities of the sperm flagella (MMAF) is a specific form of severe flagellar or ciliary deficiency syndrome. MMAF is characterized by primary infertility with abnormal morphology in the flagella of spermatozoa, presenting with short, absent, bent, coiled, and irregular flagella. As a rare disease first named in 2014, studies in recent years have shed light on the molecular defects of MMAF that comprise the structure and biological function of the sperm flagella. Understanding the molecular genetics of MMAF may provide opportunities for the development of diagnostic and therapeutic strategies for this rare disease. This review aims to summarize current studies regarding the molecular pathogenesis of MMAF and describe strategies of genetic counseling, clinical diagnosis, and therapy for MMAF.

FBXO24 deletion causes abnormal accumulation of membraneless electron-dense granules in sperm flagella and male infertility

Ribonucleoprotein (RNP) granules are membraneless electron-dense structures rich in RNAs and proteins, and involved in various cellular processes. Two RNP granules in male germ cells, intermitochondrial cement and the chromatoid body (CB), are associated with PIWI-interacting RNAs (piRNAs) and are required for transposon silencing and spermatogenesis. Other RNP granules in male germ cells, the reticulated body and CB remnants, are also essential for spermiogenesis. In this study, we disrupted FBXO24, a testis-enriched F-box protein, in mice and found numerous membraneless electron-dense granules accumulated in sperm flagella. Fbxo24 knockout (KO) mice exhibited malformed flagellar structures, impaired sperm motility, and male infertility, likely due to the accumulation of abnormal granules. The amount and localization of known RNP granule-related proteins were not disrupted in Fbxo24 KO mice, suggesting that the accumulated granules were distinct from known RNP granules. Further studies revealed that RNAs and two importins, IPO5 and KPNB1, abnormally accumulated in Fbxo24 KO spermatozoa and that FBXO24 could ubiquitinate IPO5. In addition, IPO5 and KPNB1 were recruited to stress granules, RNP complexes, when cells were treated with oxidative stress or a proteasome inhibitor. These results suggest that FBXO24 is involved in the degradation of IPO5, disruption of which may lead to the accumulation of abnormal RNP granules in sperm flagella.

Development of functional spermatozoa in mammalian spermiogenesis

Infertility is a global health problem affecting one in six couples, with 50% of cases attributed to male infertility. Spermatozoa are male gametes, specialized cells that can be divided into two parts: the head and the flagellum. The head contains a vesicle called the acrosome that undergoes exocytosis and the flagellum is a motility apparatus that propels the spermatozoa forward and can be divided into two components, axonemes and accessory structures. For spermatozoa to fertilize oocytes, the acrosome and flagellum must be formed correctly. In this Review, we describe comprehensively how functional spermatozoa develop in mammals during spermiogenesis, including the formation of acrosomes, axonemes and accessory structures by focusing on analyses of mouse models.

Genetic mutation of Cep76 results in male infertility due to abnormal sperm tail composition

The transition zone is a specialised gate at the base of cilia/flagella, which separates the ciliary compartment from the cytoplasm and strictly regulates protein entry. We identified a potential new regulator of the male germ cell transition zone, CEP76. We demonstrated that CEP76 was involved in the selective entry and incorporation of key proteins required for sperm function and fertility into the ciliary compartment and ultimately the sperm tail. In the mutant, sperm tails were shorter and immotile as a consequence of deficits in essential sperm motility proteins including DNAH2 and AKAP4, which accumulated at the sperm neck in the mutant. Severe annulus, fibrous sheath, and outer dense fibre abnormalities were also detected in sperm lacking CEP76. Finally, we identified that CEP76 dictates annulus positioning and structure. This study suggests CEP76 as a male germ cell transition zone protein and adds further evidence to the hypothesis that the spermatid transition zone and annulus are part of the same functional structure.

The lack of Tex44 causes severe subfertility with flagellar abnormalities in male mice

By analyzing a mouse Interspecific Recombinant Congenic Strain (IRCS), we previously identified a quantitative trait locus (QTL), called Mafq1 on mouse chromosome 1, that is associated with male hypofertility and ultrastructural sperm abnormalities. Within this locus, we identified a new candidate gene that could be implicated in a reproductive phenotype: Tex44 (Testis-expressed protein 44). We thus performed a CRISPR/Cas9-mediated complete deletion of this gene in mice in order to study its function. Tex44-KO males were severely hypofertile in vivo and in vitro due to a drastic reduction of sperm motility which itself resulted from important morphological sperm abnormalities. Namely, Tex44-KO sperm showed a disorganized junction between the midpiece and the principal piece of the flagellum, leading to a 180° flagellar bending in this region. In addition, the loss of some axonemal microtubule doublets and outer dense fibers in the flagellum's principal piece has been observed. Our results suggest that, in mice, TEX44 is implicated in the correct set-up of the sperm flagellum during spermiogenesis and its absence leads to flagellar abnormalities and consequently to severe male hypofertility.

FBXO24 deletion causes abnormal accumulation of membraneless electron-dense granules in sperm flagella and male infertility

Ribonucleoprotein (RNP) granules are membraneless electron-dense structures rich in RNAs and proteins, and involved in various cellular processes. Two RNP granules in male germ cells, intermitochondrial cement and the chromatoid body (CB), are associated with PIWI-interacting RNAs (piRNAs) and are required for transposon silencing and spermatogenesis. Other RNP granules in male germ cells, the reticulated body and CB remnants, are also essential for spermiogenesis. In this study, we disrupted FBXO24, a testis-enriched F-box protein, in mice and found numerous membraneless electron-dense granules accumulated in sperm flagella. Fbxo24 knockout (KO) mice exhibited malformed flagellar structures, impaired sperm motility, and male infertility, likely due to the accumulation of abnormal granules. The amount and localization of known RNP granule-related proteins were not disrupted in Fbxo24 KO mice, suggesting that the accumulated granules were distinct from known RNP granules. Further studies revealed that RNAs and two importins, IPO5 and KPNB1, abnormally accumulated in Fbxo24 KO spermatozoa and that FBXO24 could ubiquitinate IPO5. In addition, IPO5 and KPNB1 were recruited to stress granules, RNP complexes, when cells were treated with oxidative stress or a proteasome inhibitor. These results suggest that FBXO24 is involved in the degradation of IPO5, disruption of which may lead to the accumulation of abnormal RNP granules in sperm flagella.

FBXO24 modulates mRNA alternative splicing and MIWI degradation and is required for normal sperm formation and male fertility

Spermiogenesis is a critical, post-meiotic phase of male gametogenesis, in which the proper gene expression is essential for sperm maturation. However, the underFlying molecular mechanism that controls mRNA expression in the round spermatids remains elusive. Here, we identify that FBXO24, an orphan F-box protein, is highly expressed in the testis of humans and mice and interacts with the splicing factors (SRSF2, SRSF3, and SRSF9) to modulate the gene alternative splicing in the round spermatids. Genetic mutation of FBXO24 in mice causes many abnormal splicing events in round spermatids, thus affecting a large number of critical genes related to sperm formation that were dysregulated. Further molecular and phenotypical analyses revealed that FBXO24 deficiency results in aberrant histone retention, incomplete axonemes, oversized chromatoid body, and abnormal mitochondrial coiling along sperm flagella, ultimately leading to male sterility. In addition, we discovered that FBXO24 interacts with MIWI and SCF subunits and mediates the degradation of MIWI via K48-linked polyubiquitination. Furthermore, we show that FBXO24 depletion could lead to aberrant piRNA production in testes, which suggests FBXO24 is required for normal piRNA counts. Collectively, these data demonstrate that FBXO24 is essential for sperm formation by regulating mRNA alternative splicing and MIWI degradation during spermiogenesis.

The Cby3/ciBAR1 complex positions the annulus along the sperm flagellum during spermiogenesis

Proper compartmentalization of the sperm flagellum is essential for fertility. The annulus is a septin-based ring that demarcates the midpiece (MP) and the principal piece (PP). It is assembled at the flagellar base, migrates caudally, and halts upon arriving at the PP. However, the mechanisms governing annulus positioning remain unknown. We report that a Chibby3 (Cby3)/Cby1-interacting BAR domain-containing 1 (ciBAR1) complex is required for this process. Ablation of either gene in mice results in male fertility defects, caused by kinked sperm flagella with the annulus mispositioned in the PP. Cby3 and ciBAR1 interact and colocalize to the annulus near the curved membrane invagination at the flagellar pocket. In the absence of Cby3, periannular membranes appear to be deformed, allowing the annulus to migrate over the fibrous sheath into the PP. Collectively, our results suggest that the Cby3/ciBAR1 complex regulates local membrane properties to position the annulus at the MP/PP junction.

Decoding post-translational modifications of mammalian septins

Septins are cytoskeletal GTPases that form nonpolar filaments and higher-ordered structures and they take part in a wide range of cellular processes. Septins are conserved from yeast to mammals but absent from higher plants. The number of septin genes vary between organisms and they usually form complex heteropolymeric networks. Most septins are known to be capable of GTP hydrolysis which may regulate septin dynamics. Knowledge on regulation of septin function by post-translational modifications is still in its infancy. In this review article, we highlight the post-translational modifications reported for the 13 human septins and discuss their implications on septin functions. In addition to the functionally investigated modifications, we also try to make sense of the complex septin post-translational modification code revealed from large-scale phospho-proteomic datasets. Future studies may determine how these isoform-specific and homology group specific modifications affect septin structure and function.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

The cilia and flagella associated protein CFAP52 orchestrated with CFAP45 is required for sperm motility in mice

Asthenozoospermia characterized by decreased sperm motility is a major cause of male infertility, but the majority of their etiology remains unknown. Here, we showed that the cilia and flagella associated protein 52 (Cfap52) gene was predominantly expressed in testis and its deletion in a Cfap52 knockout mouse model resulted in decreased sperm motility and male infertility. Cfap52 knockout also led to the disorganization of midpiece-principal piece junction of the sperm tail, but had no effect on the axoneme ultrastructure in spermatozoa. Furthermore, we found that CFAP52 interacted with the cilia and flagella associated protein 45 (CFAP45), and knockout of Cfap52 decreased the expression level of CFAP45 in sperm flagellum, which further disrupted the microtubule sliding produced by dynein ATPase. Together, our studies demonstrate that CFAP52 plays an essential role in sperm motility by interacting with CFAP45 in sperm flagellum, providing insights into the potential pathogenesis of the infertility of the human CFAP52 mutations.

Human septins organize as octamer-based filaments and mediate actin-membrane anchoring in cells

Septins are cytoskeletal proteins conserved from algae and protists to mammals. A unique feature of septins is their presence as heteromeric complexes that polymerize into filaments in solution and on lipid membranes. Although animal septins associate extensively with actin-based structures in cells, whether septins organize as filaments in cells and if septin organization impacts septin function is not known. Customizing a tripartite split-GFP complementation assay, we show that all septins decorating actin stress fibers are octamer-containing filaments. Depleting octamers or preventing septins from polymerizing leads to a loss of stress fibers and reduced cell stiffness. Super-resolution microscopy revealed septin fibers with widths compatible with their organization as paired septin filaments. Nanometer-resolved distance measurements and single-protein tracking further showed that septin filaments are membrane bound and largely immobilized. Finally, reconstitution assays showed that septin filaments mediate actin-membrane anchoring. We propose that septin organization as octamer-based filaments is essential for septin function in anchoring and stabilizing actin filaments at the plasma membrane.

Proper phosphorylation of septin 12 regulates septin 4 and soluble adenylyl cyclase expression to induce sperm capacitation

Septin-based ring complexes maintain the sperm annulus. Defective annular structures are observed in the sperm of Sept12- and Sept4-null mice. In addition, sperm capacitation, a process required for proper fertilization, is inhibited in Sept4-null mice, implying that the sperm annulus might play a role in controlling sperm capacitation. Hence, we analyzed sperm capacitation of sperm obtained from SEPT12 Ser196 phosphomimetic (S196E), phosphorylation-deficient (S196A), and SEPT4-depleted mutant mice. Capacitation was reduced in the sperm of both the Sept12 S196E- and Sept12 S196A-knock-in mice. The protein levels of septins, namely, SEPT4 and SEPT12, were upregulated, and these proteins were concentrated in the sperm annulus during capacitation. Importantly, the expression of soluble adenylyl cyclase (sAC), a key enzyme that initiates capacitation, was upregulated, and sAC was recruited to the sperm annulus following capacitation stimulation. We further found that SEPT12, SEPT4, and sAC formed a complex and colocalized to the sperm annulus. Additionally, sAC expression was reduced and disappeared in the annulus of the SEPT12 S196E- and S196A-mutant mouse sperm. In the sperm of the SEPT4-knockout mice, sAC did not localize to the annulus. Thus, our data demonstrate that SEPT12 phosphorylation status and SEPT4 activity jointly regulate sAC protein levels and annular localization to induce sperm capacitation.

Morphological and Molecular Bases of Male Infertility: A Closer Look at Sperm Flagellum

Infertility is a major health problem worldwide without an effective therapy or cure. It is estimated to affect 8-12% of couples in the reproductive age group, equally affecting both genders. There is no single cause of infertility, and its knowledge is still far from complete, with about 30% of infertile couples having no cause identified (named idiopathic infertility). Among male causes of infertility, asthenozoospermia (i.e., reduced sperm motility) is one of the most observed, being estimated that more than 20% of infertile men have this condition. In recent years, many researchers have focused on possible factors leading to asthenozoospermia, revealing the existence of many cellular and molecular players. So far, more than 4000 genes are thought to be involved in sperm production and as regulators of different aspects of sperm development, maturation, and function, and all can potentially cause male infertility if mutated. In this review, we aim to give a brief overview of the typical sperm flagellum morphology and compile some of the most relevant information regarding the genetic factors involved in male infertility, with a focus on sperm immotility and on genes related to sperm flagellum development, structure, or function.

Case Report: Abnormalities of sperm motility and morphology in a patient with Leber hereditary optic neuropathy: Improvement after idebenone therapy

Case

We report the sperm characteristics of a male patient who developed, when he was 18 years old, a Leber hereditary optic neuropathy, a hereditary optic neuropathy due to mtDNA mutation as well as variants in the nuclear DNA. At the age of 30 years-old, he complained of infertility lasting for 2 years. Semen analyses showed low motility spermatozoa and a high percentage of morphological or ultrastructural abnormalities. Levels of epididymal markers were strongly atypical. Idebenone was prescribed as treatment of his Leber hereditary optic neuropathy in order to improve his visual acuity. After 5 months of this treatment, motility of spermatozoa increased, and their vitality improved. A natural conception occurred.

Outcome

This case is the first description of an anomaly of spermatozoas and of the epididymis epithelium in a patient with Leber hereditary optic neuropathy. It draws attention to sperm pathologies in patients with mitochondrial disorders. The role of the mtDNA mutations must be suspected since it plays an important role in the development and motility of spermatozoa. In addition, idebenone can by-pass the complex I and transfer electrons to complex III. It has been suspected to have a favorable effect on spermatogenesis.

Conclusion

This case confirms the possibility of sperm dysfunction in Leber hereditary optic neuropathy and the interest of idebenone as a treatment for infertility due to mtDNA mutations in human.

Biallelic loss-of-function mutations in SEPTIN4 (C17ORF47), encoding a conserved annulus protein, cause thin midpiece spermatozoa and male infertility in humans

Asthenoteratozoospermia is the primary cause of infertility in humans. However, the genetic etiology remains largely unknown for those suffering from severe asthenoteratozoospermia caused by thin midpiece defects. In this study, we identified two biallelic loss-of-function variants of SEPTIN4 (previously SEPT4) (Patient 1: c.A721T, p.R241* and Patient 2: c.C205T, p.R69*) in two unrelated individuals from two consanguineous Chinese families. SEPT4 is a conserved annulus protein that is critical for male fertility and the structural integrity of the sperm midpiece in mice. SEPT4 mutations disrupted the formation of SEPT-based annulus and localization of SEPTIN subunits in sperms from patients. The ultrastructural analysis demonstrated striking thin midpiece spermatozoa defects owing to annulus loss and disorganized mitochondrial sheath. Immunofluorescence and immunoblotting analyses of the mitochondrial sheath proteins TOMM20 and HSP60 further indicated that the distribution and abundance of mitochondria were impaired in men harboring biallelic SEPT4 variants. Additionally, we found that the precise localization of SLC26A8, a testis-specific anion transporter that colocalizes with SEPT4 at the sperm annulus, was missing without SEPT4. Moreover, the patient achieved a good pregnancy outcome following intracytoplasmic sperm injection. Overall, our study demonstrated for the first time that SEPT4 variants that induced thin midpiece spermatozoa defects were directly associated with human asthenoteratozoospermia.

Localization Patterns of RAB3C Are Associated with Murine and Human Sperm Formation

Background and Objectives: Septins (SEPTs) are highly conserved GTP-binding proteins and the fourth component of the cytoskeleton. Polymerization of SEPTs contributes to several critical cellular processes such as cytokinesis, cytoskeletal remodeling, and vesicle transportation. In our previous study, we found that SEPT14 mutations resulted in teratozoospermia with >87% sperm morphological defects. SEPT14 interactors were also identified through proteomic assays, and one of the peptides was mapped to RAB3B and RAB3C. Most studies on the RAB3 family have focused on RAB3A, which regulates the exocytosis of neurotransmitters and acrosome reactions. However, the general expression and patterns of the RAB3 family members during human spermatogenesis, and the association between RAB3 and teratozoospermia owing to a SEPT14 mutation, are largely unknown. Materials and Methods: Human sperm and murine male germ cells were collected in this study and immunofluorescence analysis was applied on the collected sperm. Results: In this study, we observed that the RAB3C transcripts were more abundant than those of RAB3A, 3B, and 3D in human testicular tissues. During human spermatogenesis, the RAB3C protein is mainly enriched in elongated spermatids, and RAB3B is undetectable. In mature human spermatozoa, RAB3C is concentrated in the postacrosomal region, neck, and midpiece. The RAB3C signals were delocalized within human spermatozoa harboring the SEPT14 mutation, and the decreased signals were accompanied by a defective head and tail, compared with the healthy controls. To determine whether RAB3C is involved in the morphological formation of the head and tail of the sperm, we separated murine testicular tissue and isolated elongated spermatids for further study. We found that RAB3C is particularly expressed in the manchette structure, which assists sperm head shaping at the spermatid head, and is also localized at the sperm tail. Conclusions: Based on these results, we suggest that the localization of RAB3C proteins in murine and human sperm is associated with SEPT14 mutation-induced morphological defects in sperm.

TBC1D21 is an essential factor for sperm mitochondrial sheath assembly and male fertility‡

During spermiogenesis, the formation of the mitochondrial sheath is critical for male fertility. The molecular processes that govern the development of the mitochondrial sheath remain unknown. Whether TBC1D21 serves as a GTPase-activating protein (GAP) for GTP hydrolysis in the testis is unclear, despite recent findings indicating that it collaborates with numerous proteins to regulate the formation of the mitochondrial sheath. To thoroughly examine the property of TBC1D21 in spermiogenesis, we applied the CRISPR/Cas9 technology to generate the Tbc1d21-/- mice, Tbc1d21D125A R128K mice with mutation in the GAP catalytic residues (IxxDxxR), and Tbc1d21-3xFlag mice. Male Tbc1d21-/- mice were infertile due to the curved spermatozoa flagella. In vitro fertilization is ineffective for Tbc1d21-/- sperm, although healthy offspring were obtained by intracytoplasmic sperm injection. Electron microscopy revealed aberrant ultrastructural changes in the mitochondrial sheath. Thirty-four Rab vectors were constructed followed by co-immunoprecipitation, which identified RAB13 as a novel TBC1D21 binding protein. Interestingly, infertility was not observed in Tbc1d21D125A R128K mice harboring the catalytic residue, suggesting that TBC1D21 is not a typical GAP for Rab-GTP hydrolysis. Moreover, TBC1D21 was expressed in the sperm mitochondrial sheath in Tbc1d21-3xFlag mice. Immunoprecipitation-mass spectrometry demonstrated the interactions of TBC1D21 with ACTB, TPM3, SPATA19, and VDAC3 to regulate the architecture of the sperm midpiece. The collective findings suggest that TBC1D21 is a scaffold protein required for the organization and stabilization of the mitochondrial sheath morphology.

Androglobin, a chimeric mammalian globin, is required for male fertility

Spermatogenesis is a highly specialized differentiation process driven by a dynamic gene expression program and ending with the production of mature spermatozoa. Whereas hundreds of genes are known to be essential for male germline proliferation and differentiation, the contribution of several genes remains uncharacterized. The predominant expression of the latest globin family member, androglobin (Adgb), in mammalian testis tissue prompted us to assess its physiological function in spermatogenesis. Adgb knockout mice display male infertility, reduced testis weight, impaired maturation of elongating spermatids, abnormal sperm shape, and ultrastructural defects in microtubule and mitochondrial organization. Epididymal sperm from Adgb knockout animals display multiple flagellar malformations including coiled, bifid or shortened flagella, and erratic acrosomal development. Following immunoprecipitation and mass spectrometry, we could identify septin 10 (Sept10) as interactor of Adgb. The Sept10-Adgb interaction was confirmed both in vivo using testis lysates and in vitro by reciprocal co-immunoprecipitation experiments. Furthermore, the absence of Adgb leads to mislocalization of Sept10 in sperm, indicating defective manchette and sperm annulus formation. Finally, in vitro data suggest that Adgb contributes to Sept10 proteolysis in a calmodulin-dependent manner. Collectively, our results provide evidence that Adgb is essential for murine spermatogenesis and further suggest that Adgb is required for sperm head shaping via the manchette and proper flagellum formation.

CEP128 is involved in spermatogenesis in humans and mice

Centrosomal proteins are necessary components of the centrosome, a conserved eukaryotic organelle essential to the reproductive process. However, few centrosomal proteins have been genetically linked to fertility. Herein we identify a homozygous missense variant of CEP128 (c.665 G > A [p.R222Q]) in two infertile males. Remarkably, male homozygous knock-in mice harboring the orthologous CEP128^R222Q variant show anomalies in sperm morphology, count, and motility. Moreover, Cep128 knock-out mice manifest male infertility associated with disrupted sperm quality. We observe defective sperm flagella in both homozygous Cep128 KO and KI mice; the cilia development in other organs is normal—suggesting that CEP128 variants predominantly affected the ciliogenesis in the testes. Mechanistically, CEP128 is involved in male reproduction via regulating the expression of genes and/or the phosphorylation of TGF-β/BMP-signalling members during spermatogenesis. Altogether, our findings unveil a crucial role for CEP128 in male fertility and provide important insights into the functions of centrosomal proteins in reproductive biology.

CEP128 is a centrosomal protein important for the organization of centriolar microtubules. Here, the authors show that a CEP128 variant observed in human male siblings causes reduced sperm counts and morphologically abnormal sperm when modeled in mice, suggesting a role for CEP128 in male fertility.

Molecular basis of the morphogenesis of sperm head and tail in mice

Background

The spermatozoon has a complex molecular apparatus necessary for fertilization in its head and flagellum. Recently, numerous genes that are needed to construct the molecular apparatus of spermatozoa have been identified through the analysis of genetically modified mice.

Methods

Based on the literature information, the molecular basis of the morphogenesis of sperm heads and flagella in mice was summarized.

Main findings (Results)

The molecular mechanisms of vesicular trafficking and intraflagellar transport in acrosome and flagellum formation were listed. With the development of cryo‐electron tomography and mass spectrometry techniques, the details of the axonemal structure are becoming clearer. The fine structure and the proteins needed to form the central apparatus, outer and inner dynein arms, nexin‐dynein regulatory complex, and radial spokes were described. The important components of the formation of the mitochondrial sheath, fibrous sheath, outer dense fiber, and the annulus were also described. The similarities and differences between sperm flagella and Chlamydomonas flagella/somatic cell cilia were also discussed.

Conclusion

The molecular mechanism of formation of the sperm head and flagellum has been clarified using the mouse as a model. These studies will help to better understand the diversity of sperm morphology and the causes of male infertility.

Identification and Structure Prediction of Human Septin-4 as a Biomarker for Diagnosis of Asthenozoospermic Infertile Patients-Critical Finding Toward Personalized Medicine

Semen parameters are been found as a key factor to evaluate the count and morphology in the given semen sample. The deep knowledge of male infertility will unravel with semen parameters correlated with molecular and biochemical parameters. The current research study is to identify the motility associated protein and its structure through the in-silico approach. Semen samples were collected and initial analysis including semen parameters was analyzed by using the World Health Organization protocol. Semen biochemical parameters, namely, seminal plasma protein concentration, fructose content, and glucosidase content were calculated and evaluated for correlation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) were carried out for identification of Septin-4 presence in the semen sample. Mascot search was done for protein conformation and in-silico characterization of Septin-4 by structural modeling in Iterative Threading Assembly Refinement (I-TASSER). Twenty-five nanoseconds molecular dynamics (MD) simulations results showed the stable nature of Septin-4 in the dynamic system. Overall, our results showed the presence of motility-associated protein in normospermia and control samples and not in the case of asthenospermia and oligoasthenospermia. Molecular techniques characterized the presence of Septin-4 and as a novel biomarker for infertility diagnosis.

Novel biallelic mutations in SLC26A8 cause severe asthenozoospermia in humans owing to midpiece defects: Insights into a putative dominant genetic disease

To investigate the genetic cause of male infertility characterized by severe asthenozoospermia, two unrelated infertile men with severe asthenozoospermia from nonconsanguineous Chinese families were enrolled, and whole exome sequencing were performed to identify the potential pathogenic mutations. Novel compound heterozygous mutations (NK062 III-1: c.290T>C, p.Leu97Pro; c.1664delT, p.Ile555Thrfs*11/NK038 III-1: c.212G>T, p.Arg71Leu; c.290T>C, p.Leu97Pro) in SLC26A8 were identified. All mutations were inherited from their heterozygous parents and are predicted to be disease-causing by sorts intolerant from tolerant, PolyPhen-2, Mutation Taster, and Combined Annotation Dependent Depletion. In silico mutant SLC26A8 models predict that mutations p.Leu97Pro and p.Arg71Leu cause changes in the α-helix, which may result in functional defects in the protein. Notably, heterozygous male carriers of each mutation in both families were able to reproduce naturally, which is inconsistent with previous reports. Ultrastructural analysis revealed severe asthenozoospermia associated with absence of the mitochondrial sheath and annulus in spermatozoa from both the probands, and both structural defects were verified by HSP60 and SEPT4 immunofluorescence analysis. SLC26A8 levels were significantly reduced in spermatozoa from patients harboring biallelic SLC26A8 mutations, and both patients achieved good prognosis following intracytoplasmic sperm injection. Our findings indicate that mutations in SLC26A8 could manifest as a recessive genetic cause of severe asthenozoospermia and male infertility.

Septin Assembly and Remodeling at the Cell Division Site During the Cell Cycle

The septin family of proteins can assemble into filaments that further organize into different higher order structures to perform a variety of different functions in different cell types and organisms. In the budding yeast Saccharomyces cerevisiae, the septins localize to the presumptive bud site as a cortical ring prior to bud emergence, expand into an hourglass at the bud neck (cell division site) during bud growth, and finally “split” into a double ring sandwiching the cell division machinery during cytokinesis. While much work has been done to understand the functions and molecular makeups of these structures, the mechanisms underlying the transitions from one structure to another have largely remained elusive. Recent studies involving advanced imaging and in vitro reconstitution have begun to reveal the vast complexity involved in the regulation of these structural transitions, which defines the focus of discussion in this mini-review.

Effects of Calyculin a on the Motility and Protein Phosphorylation in Frozen-Thawed Bull Spermatozoa

In this study, we examined the effects of calyculin A, a phosphatase inhibitor, on motility, protein phosphorylation, and the distribution of phospho-(Ser/Thr) PKA substrates in frozen-thawed bull spermatozoa that are actually used by most farmers for breeding. The data showed that calyculin A, which has been reported to have a positive effect on the motility of ejaculated fresh spermatozoa, distinctly decreased the motility of frozen-thawed bull spermatozoa even if a cell activator, such as caffeine, was present in the incubation medium and that the suppressive effect of calyculin A was dose-dependent and continued for at least 200 min. Immunoblot analyses revealed that de novo protein phosphorylation was not detected in spermatozoa exposed to caffeine or dbcAMP (a cell-permeable cAMP analog), while the addition of calyculin A to the medium brought about the appearance of several phosphorylated proteins at 50 kDa and 75 kDa, suggesting that 50 kDa and 75 kDa proteins, which were phosphorylated by activation of cAMP-dependent PKA, were not dephosphorylated and were accumulated in spermatozoa due to the suppression of calyculin A-sensitive protein phosphatases. Immunofluorescence microscopy revealed that calyculin A caused, alone or in conjunction with caffeine or dbcAMP, the accumulation of phospho-PKA substrates at the annulus, although caffeine or dbcAMP alone did not. This study suggested that calyculin A decreases the motility of frozen-thawed bull spermatozoa concomitant with the accumulation of phospho-(Ser/Thr) PKA substrates at the annulus of flagella.

Evaluation of SEPT2 and SEPT4 transcript contents in spermatozoa from men with asthenozoospermia and teratozoospermia

BACKGROUND AND AIMS

Motility and morphological defects of spermatozoa can cause male infertility. Sperm RNAs are related to sperm quality. They are considered to have clinical values as a biomarker for assessing sperm quality and fertility potential. The annulus, located in the mammalian sperm tail, is required for motility and terminal differentiation of the spermatozoa. SEPT2, 4, 6, 7, and 12 proteins are the main components of the annulus in the sperm tail. The study aimed to evaluate SEPT2 and SEPT4 mRNA contents in the spermatozoa of patients with asthenozoospermia and teratozoospermia.

METHODS

We evaluated transcript levels of SEPT2 and SEPT4 in the sperm samples of 20 asthenozoospermic, 20 teratozoospermic, and 20 normozoospermic samples using quantitative PCR.

RESULTS

The SEPT2 transcript level was significantly decreased in the asthenozoospermia samples compared with the normal group (P = .013). However, SEPT4 was not significantly different between these two groups. The transcript levels of SEPT2 and SEPT4 were not statistically different between teratozoospermic and normozoospermic groups.

CONCLUSION

In conclusion, downregulation of SEPT2 in patients with asthenozoospermia appears to be associated with poor sperm motility.

Dependence of sperm structural and functional integrity on testicular calcineurin isoform PPP3R2 expression

After leaving the testis, mammalian sperm undergo a sequential maturation process in the epididymis followed by capacitation during their movement through the female reproductive tract. These phenotypic changes are associated with modification of protein phosphorylation and membrane remodeling, which is requisite for sperm to acquire forward motility and induce fertilization. However, the molecular mechanisms underlying sperm maturation and capacitation are still not fully understood. Herein, we show that PPP3R2, a testis-specific regulatory subunit of protein phosphatase 3 (an isoform of calcineurin in the testis), is essential for sperm maturation and capacitation. Knockout of Ppp3r2 in mice leads to male sterility due to sperm motility impairment and morphological defects. One very noteworthy change includes increases in sperm membrane stiffness. Moreover, PPP3R2 regulates sperm maturation and capacitation via (i) modulation of membrane diffusion barrier function at the annulus and (ii) facilitation of cholesterol efflux during sperm capacitation. Taken together, PPP3R2 plays a critical role in modulating cholesterol efflux and mediating the dynamic control of membrane remodeling during sperm maturation and capacitation.

The SEPT12 complex is required for the establishment of a functional sperm head-tail junction

The connecting pieces of the sperm neck link the flagellum and the sperm head, and they are important for initiating flagellar beating. The connecting pieces are important building blocks for the sperm neck; however, the mechanism of connecting piece assembly is poorly understood. In the present study, we explored the role of septins in sperm motility and found that Sept12D197N knock-in (KI) mice produce acephalic and immotile spermatozoa. Electron microscopy analysis showed defective connecting pieces in sperm from KI mice, indicating that SEPT12 is required for the establishment of connecting pieces. We also found that SEPT12 formed a complex with SEPT1, SEPT2, SEPT10 and SEPT11 at the sperm neck and that the D197N mutation disrupted the complex, suggesting that the SEPT12 complex is involved in the assembly of connecting pieces. Additionally, we found that SEPT12 interacted and colocalized with γ-tubulin in elongating spermatids, implying that SEPT12 and pericentriolar materials jointly contribute to the formation of connecting pieces. Collectively, our findings suggest that SEPT12 is required for the formation of striated columns, and the capitulum and for maintaining the stability of the sperm head-tail junction.

Septin 4 controls CCNB1 stabilization via APC/CCDC20 during meiotic G2/M transition in mouse oocytes

In mammals, oocytes are arrested at G2/prophase for a long time, which is called germinal vesicle (GV) arrest. After puberty, fully-grown oocytes are stimulated by a gonadotropin surge to resume meiosis as indicated by GV breakdown (GVBD). CCNB1 is accumulated to a threshold level to trigger the activation of maturation promoting factor (MPF), inducing the G2/M transition. It is generally recognized that the anaphase-promoting complex/cyclosome (APC/C) and its cofactor CDH1 (also known as FZR1) regulates the accumulation/degradation of CCNB1. Here, by using small interfering RNA (siRNA) and messenger RNA (mRNA) microinjection, immunofluorescence and confocal microscopy, immunoprecipitation, time-lapse live imaging, and immunoblotting analysis, we showed that Septin 4 regulates the G2/M transition by regulating the accumulation of CCNB1 via APC/C^CDC20 . Depletion of Septin 4 caused GV arrest by reducing CCNB1 accumulation. Unexpectedly, the expression level of CDC20 was higher in Septin 4 siRNA-injected oocytes than in control oocytes, but there was no significant change in the expression level of CDH1. Importantly, the reduced GVBD after Septin 4 depletion could be rescued not only by over-expressing CCNB1 but also could be partially rescued by depleting CDC20. Taken together, our results demonstrate that Septin 4 may play a critical role in meiotic G2/M transition by indirect regulation of CCNB1 stabilization in mouse oocytes.

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

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

SEPTIN12 c.474 G > A polymorphism as a risk factor in teratozoospermic patients

Teratozoospermia is a condition related to poor morphologically normal sperm count below the lower reference limit, which could hinder natural conception. Single nucleotide polymorphisms (SNPs) in the genes involved in sperm production and testicular function are proved to be risk factors, resulting in decreased sperm parameters and defects in sperm morphology. c.474 G > A polymorphism in the SEPTIN12 gene which is one of the testis-specific genes creates a novel splice variant and the resulting truncated protein was previously found to be more prevalent in infertile men. We aimed to investigate the association of SEPTIN12 c.474 G > A polymorphism with male infertility in teratozoospermia patients. Forty-eight teratozoospermic patients, diagnosed according to Kruger's criteria and 164 fertile controls who fathered at least 1 child within 3 years without assisted reproductive technologies were included into our prospective randomized controlled study. PCR-RFLP method was used for genotyping. Although no statistical difference was found between teratozoospermic patients and fertile controls in terms of genotype distributions, significance was identified between the genotypes of all and non-smoking teratozoopermic patients in terms of neck defects. SEPTIN12 c.474 G > A polymorphism was shown to be associated with sperm neck defects in teratozoospermic patients using the dominant statistical model. Smoking was identified as a risk factor for the sperm morphology defects in teratozoospermic A allele carriers.

Membrane binding controls ordered self-assembly of animal septins

Septins are conserved cytoskeletal proteins that regulate cell cortex mechanics. The mechanisms of their interactions with the plasma membrane remain poorly understood. Here, we show by cell-free reconstitution that binding to flat lipid membranes requires electrostatic interactions of septins with anionic lipids and promotes the ordered self-assembly of fly septins into filamentous meshworks. Transmission electron microscopy reveals that both fly and mammalian septin hexamers form arrays of single and paired filaments. Atomic force microscopy and quartz crystal microbalance demonstrate that the fly filaments form mechanically rigid, 12- to 18-nm thick, double layers of septins. By contrast, C-terminally truncated septin mutants form 4-nm thin monolayers, indicating that stacking requires the C-terminal coiled coils on DSep2 and Pnut subunits. Our work shows that membrane binding is required for fly septins to form ordered arrays of single and paired filaments and provides new insights into the mechanisms by which septins may regulate cell surface mechanics.

p53 induces ARTS to promote mitochondrial apoptosis

Apoptosis related protein in TGF-β signaling pathway (ARTS) was originally discovered in cells undergoing apoptosis in response to TGF-β, but ARTS also acts downstream of many other apoptotic stimuli. ARTS induces apoptosis by antagonizing the anti-apoptotic proteins XIAP and Bcl-2. Here we identified the pro-apoptotic Sept4/ARTS gene as a p53-responsive target gene. Ectopic p53 and a variety of p53-inducing agents increased both mRNA and protein levels of ARTS, whereas ablation of p53 reduced ARTS expression in response to multiple stress conditions. Also, γ-irradiation induced p53-dependent ARTS expression in mice. Consistently, p53 binds to the responsive DNA element on the ARTS promoter and transcriptionally activated the promoter-driven expression of a luciferase reporter gene. Interestingly, ARTS binds to and sequesters p53 at mitochondria, enhancing the interaction of the latter with Bcl-XL. Ectopic ARTS markedly augments DNA damage stress- or Nutlin-3-triggered apoptosis, while ablation of ARTS preferentially impairs p53-induced apoptosis. Altogether, these findings demonstrate that ARTS collaborates with p53 in mitochondria-engaged apoptosis.

Cabs1 Maintains Structural Integrity of Mouse Sperm Flagella during Epididymal Transit of Sperm

The calcium-binding protein spermatid-associated 1 (Cabs1) is a novel spermatid-specific protein. However, its function remains largely unknown. In this study, we found that a long noncoding RNA (lncRNA) transcripted from the Cabs1 gene antisense, AntiCabs1, was also exclusively expressed in spermatids. Cabs1 and AntiCabs1 knockout mice were generated separately (using Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)-Cas9 methods) to investigate their functions in spermatogenesis. The genetic loss of Cabs1 did not affect testicular and epididymal development; however, male mice exhibited significantly impaired sperm tail structure and subfertility. Ultrastructural analysis revealed defects in sperm flagellar differentiation leading to an abnormal annulus and disorganization of the midpiece-principal piece junction, which may explain the high proportion of sperm with a bent tail. Interestingly, the proportion of sperm with a bent tail increased during transit in the epididymis. Furthermore, Western blot and immunofluorescence analyses showed that a genetic loss of Cabs1 decreased Septin 4 and Krt1 and increased cyclin Y-like 1 (Ccnyl1) levels compared with the wild type, suggesting that Cabs1 deficiency disturbed the expression of cytoskeleton-related proteins. By contrast, AntiCabs1^-/- mice were indistinguishable from the wild type regarding testicular and epididymal development, sperm morphology, concentration and motility, and male fertility. This study demonstrates that Cabs1 is an important component of the sperm annulus essential for proper sperm tail assembly and motility.

Integrated analysis of phosphoproteome and ubiquitylome in epididymal sperm of buffalo (Bubalus bubalis)

In mammals, sperm need to mature in the epididymis to gain fertilization competency. However, the molecular mechanism underlying buffalo sperm maturation remains elusive. Exploring sperm physiology at the posttranslational modification (PTM) level could help to develop our understanding of these mechanisms. Protein phosphorylation and ubiquitination are major PTMs in the regulation of many biological processes. In the present study, to our knowledge, we report the first phosphoproteome and ubiquitylome of sperm collected from the caput, corpus, and cauda segments of the epididymis using liquid chromatography-mass spectrometry combined with affinity purification. In total, 647 phosphorylation sites in 294 proteins and 1063 ubiquitination sites in 446 proteins were characterized. Some of these proteins were associated with cellular developmental processes and energy metabolic pathways. Interestingly, 84 proteins were both phosphorylated and ubiquitinated, simultaneously. Some of these proteins were involved in, for example, spermatogenesis, reproduction, and spermatid development. Taken together, these data provide a theoretical basis for further functional analysis of phosphorylation and ubiquitination in epididymal sperm of buffalo and other mammals, and serve as an important resource for exploring the physiological mechanism underlying sperm maturation.

Genetic underpinnings of asthenozoospermia

Asthenozoospermia (AZS), defined by reduced motility or absent sperm motility, is one of the main causes of male infertility. This condition may be divided into isolated AZS in the absence of other symptoms and syndromic AZS, which is characterized by several concurrent clinical symptoms. Sperm motility depends on fully functional flagellum, energy availability, and the crosstalk of several signaling pathways; therefore, mutations in genes involved in flagellar assembly and motile regulation can cause AZS. Thus, it is crucial to understand the genetic causes and mechanisms contributing to AZS. In this review, we summarize the current knowledge about the particular genes and mechanisms involved in intact flagellum, energy availability, and signaling transduction that could cause human AZS and discuss the respective gene defects known to be responsible for these abnormalities. Additionally, we discuss intracytoplasmic sperm injection outcomes and offspring health where available in these cases.

ACTN4 Mediates SEPT14 Mutation-Induced Sperm Head Defects

Septins (SEPTs) are highly conserved GTP-binding proteins and the fourth component of the cytoskeleton. Polymerized SEPTs participate in the modulation of various cellular processes, such as cytokinesis, cell polarity, and membrane dynamics, through their interactions with microtubules, actin, and other cellular components. The main objective of this study was to dissect the molecular pathological mechanism of SEPT14 mutation-induced sperm head defects. To identify SEPT14 interactors, co-immunoprecipitation (co-IP) and nano-liquid chromatography-mass spectrometry/mass spectrometry were applied. Immunostaining showed that SEPT14 was significantly localized to the manchette structure. The SEPT14 interactors were identified and classified as (1) SEPT-, (2) microtubule-, (3) actin-, and (4) sperm structure-related proteins. One interactor, ACTN4, an actin-holding protein, was selected for further study. Co-IP experiments showed that SEPT14 interacts with ACTN4 in a male germ cell line. SEPT14 also co-localized with ACTN4 in the perinuclear and manchette regions of the sperm head in early elongating spermatids. In the cell model, mutated SEPT14 disturbed the localization pattern of ACTN4. In a clinical aspect, sperm with mutant SEPT14, SEPT14^A123T (p.Ala123Thr), and SEPT14^I333T (p.Ile333Thr), have mislocalized and fragmented ACTN4 signals. Sperm head defects in donors with SEPT14 mutations are caused by disruption of the functions of ACTN4 and actin during sperm head formation.

A small-molecule ARTS mimetic promotes apoptosis through degradation of both XIAP and Bcl-2

Many human cancers over-express B cell lymphoma 2 (Bcl-2) or X-linked inhibitor of apoptosis (IAP) proteins to evade cell death. The pro-apoptotic ARTS (Sept4_i2) protein binds directly to both Bcl-2 and XIAP and promotes apoptosis by stimulating their degradation via the ubiquitin-proteasome system (UPS). Here we describe a small molecule, A4, that mimics the function of ARTS. Microscale thermophoresis assays showed that A4 binds XIAP, but not cellular inhibitor of apoptosis protein 1 (cIAP1). A4 binds to a distinct ARTS binding pocket in the XIAP-BIR3 (baculoviral IAP repeat 3) domain. Like ARTS, A4 stimulated poly-ubiquitylation and UPS-mediated degradation of XIAP and Bcl-2, but not cIAP1, resulting in caspase-9 and -3 activation and apoptosis. In addition, over-expression of XIAP rescued HeLa cells from A4-induced apoptosis, consistent with the idea that A4 kills by antagonizing XIAP. On the other hand, treatment with the SMAC-mimetic Birinapant induced secretion of tumour necrosis factor-α (TNFα) and killed ~50% of SKOV-3 cells, and addition of A4 to Birinapant-treated cells significantly reduced secretion of TNFα and blocked Birinapant-induced apoptosis. This suggests that A4 acts by specifically targeting XIAP. The effect of A4 was selective as peripheral blood mononuclear cells and normal human breast epithelial cells were unaffected. Furthermore, proteome analysis revealed that cancer cell lines with high levels of XIAP were particularly sensitive to the killing effect of A4. These results provide proof of concept that the ARTS binding site in XIAP is "druggable". A4 represents a novel class of dual-targeting compounds stimulating apoptosis by UPS-mediated degradation of important anti-apoptotic oncogenes.

Septin4 promotes cell death in human colon cancer cells by interacting with BAX

Septin4 is a tumor suppressor protein that promotes cell programmed death in various cell types through specifically antagonizing XIAP (X linked inhibitor of apoptosis), little is known its other novel binding partner and role in colorectal cancer. In this study, we found that Septin4 significantly expressed lower in human colon cancer when compared to peri-tumor benign cells, and its low expression was significantly associated with worse prognostic outcomes. Furthermore, Septin4 participated in DOX-induced colon cancer cell death in vitro. Septin4-overexpressing colon cancer cells displayed augmented apoptotic cell death and ROS production. Additionally, Septin4-knockdown cells revealed a resistance of DOX-induced cell death and reduced ROS production. Importantly, we first identified that BAX is a novel Septin4 binding partner and the interaction is enhanced under DOX treatment. Finally, Septin4-knockdown promoted colon cells growth in vivo. These observations suggest that Septin4 as an essential molecule contribute to the occurrence and development of human colon cancer and provide new technical approaches for targeted treatment of this disease.

A framework for high-resolution phenotyping of candidate male infertility mutants: from human to mouse

Male infertility is a heterogeneous condition of largely unknown etiology that affects at least 7% of men worldwide. Classical genetic approaches and emerging next-generation sequencing studies support genetic variants as a frequent cause of male infertility. Meanwhile, the barriers to transmission of this disease mean that most individual genetic cases will be rare, but because of the large percentage of the genome required for spermatogenesis, the number of distinct causal mutations is potentially large. Identifying bona fide causes of male infertility thus requires advanced filtering techniques to select for high-probability candidates, including the ability to test causality in animal models. The mouse remains the gold standard for defining the genotype-phenotype connection in male fertility. Here, we present a best practice guide consisting of (a) major points to consider when interpreting next-generation sequencing data performed on infertile men, and, (b) a systematic strategy to categorize infertility types and how they relate to human male infertility. Phenotyping infertility in mice can involve investigating the function of multiple cell types across the testis and epididymis, as well as sperm function. These findings will feed into the diagnosis and treatment of male infertility as well as male health broadly.