The axoneme: the propulsive engine of spermatozoa and cilia and associated ciliopathies leading to infertility

Insights into crucial molecules and protein channels involved in pig sperm cryopreservation

Cryopreservation is the most efficient procedure for long-term preservation of mammalian sperm; however, its use is not currently dominant for boar sperm before its use for artificial insemination. In fact, freezing and thawing have an extensive detrimental effect on sperm function and lead to impaired fertility. The present work summarises the basis of the structural and functional impact of cryopreservation on pig sperm that have been extensively studied in recent decades, as well as the molecular alterations in sperm that are related to this damage. The wide variety of mechanisms underlying the consequences of alterations in expression levels and structural modifications of sperm proteins with diverse functions is detailed. Moreover, the use of cryotolerance biomarkers as predictors of the potential resilience of a sperm sample to the cryopreservation process is also discussed. Regarding the proteins that have been identified to be relevant during the cryopreservation process, they are classified according to the functions they carry out in sperm, including antioxidant function, plasma membrane protection, sperm motility regulation, chromatin structure, metabolism and mitochondrial function, heat-shock response, premature capacitation and sperm-oocyte binding and fusion. Special reference is made to the relevance of sperm membrane channels, as their function is crucial for boar sperm to withstand osmotic shock during cryopreservation. Finally, potential aims for future research on cryodamage and cryotolerance are proposed, which might be crucial to minimise the side-effects of cryopreservation and to make it a more advantageous strategy for boar sperm preservation.

Spermatocytes have the capacity to segregate chromosomes despite centriole duplication failure

Centrosomes are the canonical microtubule organizing centers (MTOCs) of most mammalian cells, including spermatocytes. Centrosomes comprise a centriole pair within a structurally ordered and dynamic pericentriolar matrix (PCM). Unlike in mitosis, where centrioles duplicate once per cycle, centrioles undergo two rounds of duplication during spermatogenesis. The first duplication is during early meiotic prophase I, and the second is during interkinesis. Using mouse mutants and chemical inhibition, we have blocked centriole duplication during spermatogenesis and determined that non-centrosomal MTOCs (ncMTOCs) can mediate chromosome segregation. This mechanism is different from the acentriolar MTOCs that form bipolar spindles in oocytes, which require PCM components, including gamma-tubulin and CEP192. From an in-depth analysis, we identified six microtubule-associated proteins, TPX2, KIF11, NuMA, and CAMSAP1-3, that localized to the non-centrosomal MTOC. These factors contribute to a mechanism that ensures bipolar MTOC formation and chromosome segregation during spermatogenesis when centriole duplication fails. However, despite the successful completion of meiosis and round spermatid formation, centriole inheritance and PLK4 function are required for normal spermiogenesis and flagella assembly, which are critical to ensure fertility.

Cysteine supplementation pre-freeze and post-thaw improves integrity and reduces oxidative stress in cryopreserved ram spermatozoa

Cryopreserved ram sperm is highly sensitive to oxidative stress by reactive oxygen species (ROS) which impair sperm function and integrity. Antioxidants such as cysteine can mitigate the effect of ROS, although the optimal concentration or timing of supplementation is unknown. This study aimed to determine the effect of concentration and timing of cysteine supplementation on the integrity and function of cryopreserved ram spermatozoa. Nine ejaculates were collected from three Texel rams then cryopreserved and supplemented with cysteine (0, 0.5, or 1.0 mg/mL) added pre-freeze (PF), post-thaw (PT) or pre-freeze and post-thaw (PF + PT) generating seven treatments: 1) control 0 mg/mL, 2) PF 0.5 mg/mL, 3) PF 1 mg/mL, 4) PT 0.5 mg/mL, 5), PT 1.0 mg/mL, 6) PF + PT 0.5 mg/mL and 7) PF + PT 1.0 mg/mL. Sperm motility, viability, acrosome integrity, ROS production and penetrability through artificial cervical mucus were assessed post-thaw. Cysteine supplementation reduced ROS production which thereby improved spermatozoa motility, viability, acrosome integrity and penetrability (p < 0.001) Sperm integrity for all parameters was greatest in spermatozoa treated PF + PT with 1.0 mg/mL cysteine, although treatment pre-freeze or post-thaw also improved integrity beyond the control. This study has identified that 1.0 mg/mL cysteine is most beneficial and has highlighted the importance of preventing oxidative stress in spermatozoa post-thaw. These finding can help to mitigate the detrimental effect of cryopreservation on spermatozoa and aid the development of cryopreservation protocols in sheep.

Dual-allele heterozygous mutation of DNAH5 gene in a boy with primary ciliary dyskinesia: A case report

RATIONALE

To analyze clinical and imaging features, ciliary structure and family gene mutation loci of a primary ciliary dyskinesia (PCD) boy with a dual-allele heterozygous mutation of DNAH5.

PATIENT CONCERNS

Clinical data of the proband and relatives. Electronic bronchoscopy, transmission electron microscope (TEM) of the cilia and next-generation sequencing (NGS) were performed. PCD-related DNAH5 exon mutation sites were searched.

DIAGNOSES

A 10-year and 10-month-old boy was hospitalized due to "recurrent cough, expectoration, sputum and shortness of breathing after activity for over 7 years, and aggravated for 1 week." Moderate and fine wet rales were detected in bilateral lungs. Clubbing fingers and toes were observed. In local hospitals, he was diagnosed with Mycoplasma pneumoniae infection and Streptococcus pneumoniae was cultured.

INTERVENTIONS

Pulmonary function testing showed mixed ventilation dysfunction and positive for bronchial dilation test. Imaging examination and fiberoptic bronchoscopy revealed transposition of all viscera, bilateral pneumonia, and bronchiectasis. TEM detected no loss of the outer dynein arms. NGS identified 2 mutations (c.4360C>T, c.9346C>T) in the DNAH5 gene inherited from healthy parents.

OUTCOMES

According to literature review until 2022, among 144 exon gene mutations causing amino acid changes, C>T mutation is the most common in 44 cases, followed by deletion mutations in 30 cases. Among the amino acid changes induced by gene mutation, terminated mutations were identified in 89 cases.

LESSONS

For suspected PCD patients, TEM and NGS should be performed. Prompt diagnosis and treatment may delay the incidence of bronchiectasis and improve clinical prognosis.

In-cell structural insight into the stability of sperm microtubule doublet

The propulsion for mammalian sperm swimming is generated by flagella beating. Microtubule doublets (DMTs) along with microtubule inner proteins (MIPs) are essential structural blocks of flagella. However, the intricate molecular architecture of intact sperm DMT remains elusive. Here, by in situ cryo-electron tomography, we solved the in-cell structure of mouse sperm DMT at 4.5-7.5 Å resolutions, and built its model with 36 kinds of MIPs in 48 nm periodicity. We identified multiple copies of Tektin5 that reinforce Tektin bundle, and multiple MIPs with different periodicities that anchor the Tektin bundle to tubulin wall. This architecture contributes to a superior stability of A-tubule than B-tubule of DMT, which was revealed by structural comparison of DMTs from the intact and deformed axonemes. Our work provides an overall molecular picture of intact sperm DMT in 48 nm periodicity that is essential to understand the molecular mechanism of sperm motility as well as the related ciliopathies.

De novo protein identification in mammalian sperm using in situ cryoelectron tomography and AlphaFold2 docking

To understand the molecular mechanisms of cellular pathways, contemporary workflows typically require multiple techniques to identify proteins, track their localization, and determine their structures in vitro. Here, we combined cellular cryoelectron tomography (cryo-ET) and AlphaFold2 modeling to address these questions and understand how mammalian sperm are built in situ. Our cellular cryo-ET and subtomogram averaging provided 6.0-Å reconstructions of axonemal microtubule structures. The well-resolved tertiary structures allowed us to unbiasedly match sperm-specific densities with 21,615 AlphaFold2-predicted protein models of the mouse proteome. We identified Tektin 5, CCDC105, and SPACA9 as novel microtubule-associated proteins. These proteins form an extensive interaction network crosslinking the lumen of axonemal doublet microtubules, suggesting their roles in modulating the mechanical properties of the filaments. Indeed, Tekt5 -/- sperm possess more deformed flagella with 180° bends. Together, our studies presented a cellular visual proteomics workflow and shed light on the in vivo functions of Tektin 5.

Sperm centriolar factors and genetic defects that can predict pregnancy

The human sperm centrosome, comprising the two morphologically distinct centrioles and associated pericentriolar materials, plays a crucial role in fertilization and early embryonic development after fertilization. Once inside the oocyte, the sperm centrosome serves as a microtubule-organizing center, orchestrating mitotic spindle formation, chromosome segregation, and syngamy. Abnormalities of the sperm centrosome can lead to abnormal embryonic development and embryonic chromosomal instability, and are associated with pregnancy loss. Recent research has shed light on the molecular composition, regulation, and function of this vital organelle. Understanding the intricacies of the sperm centrosome is crucial for elucidating the mechanisms underlying successful fertilization and early embryonic development, as well as addressing infertility and developmental disorders associated with centrosomal defects.

Phosphoinositides in New Spaces

Phosphoinositides (PIs) are phospholipids derived from phosphatidylinositol. PIs are regulated via reversible phosphorylation, which is directed by the opposing actions of PI kinases and phosphatases. PIs constitute a minor fraction of the total cellular lipid pool but play pleiotropic roles in multiple aspects of cell biology. Genetic mutations of PI regulatory enzymes have been identified in rare congenital developmental syndromes, including ciliopathies, and in numerous human diseases, such as cancer and metabolic and neurological disorders. Accordingly, PI regulatory enzymes have been targeted in the design of potential therapeutic interventions for human diseases. Recent advances place PIs as central regulators of membrane dynamics within functionally distinct subcellular compartments. This brief review focuses on the emerging role PIs play in regulating cell signaling within the primary cilium and in directing transfer of molecules at interorganelle membrane contact sites and identifies new roles for PIs in subcellular spaces.

In situ cryo-electron tomography reveals the asymmetric architecture of mammalian sperm axonemes

The flagella of mammalian sperm display non-planar, asymmetric beating, in contrast to the planar, symmetric beating of flagella from sea urchin sperm and unicellular organisms. The molecular basis of this difference is unclear. Here, we perform in situ cryo-electron tomography of mouse and human sperm, providing the highest-resolution structural information to date. Our subtomogram averages reveal mammalian sperm-specific protein complexes within the microtubules, the radial spokes and nexin-dynein regulatory complexes. The locations and structures of these complexes suggest potential roles in enhancing the mechanical strength of mammalian sperm axonemes and regulating dynein-based axonemal bending. Intriguingly, we find that each of the nine outer microtubule doublets is decorated with a distinct combination of sperm-specific complexes. We propose that this asymmetric distribution of proteins differentially regulates the sliding of each microtubule doublet and may underlie the asymmetric beating of mammalian sperm.

DNALI1 deficiency causes male infertility with severe asthenozoospermia in humans and mice by disrupting the assembly of the flagellar inner dynein arms and fibrous sheath

The axonemal dynein arms (outer (ODA) and inner dynein arms (IDAs)) are multiprotein structures organized by light, intermediate, light intermediate (LIC), and heavy chain proteins. They hydrolyze ATP to promote ciliary and flagellar movement. Till now, a variety of dynein protein deficiencies have been linked with asthenospermia (ASZ), highlighting the significance of these structures in human sperm motility. Herein, we detected bi-allelic DNALI1 mutations [c.663_666del (p.Glu221fs)], in an ASZ patient, which resulted in the complete loss of the DNALI1 in the patient's sperm. We identified loss of sperm DNAH1 and DNAH7 rather than DNAH10 in both DNALI1^663_666del patient and Dnali1^-/- mice, demonstrating that mammalian DNALI1 is a LIC protein of a partial IDA subspecies. More importantly, we revealed that DNALI1 loss contributed to asymmetries in the most fibrous sheath (FS) of the sperm flagellum in both species. Immunoprecipitation revealed that DNALI1 might interact with the cytoplasmic dynein complex proteins in the testes. Furthermore, DNALI1 loss severely disrupted the transport and assembly of the FS proteins, especially AKAP3 and AKAP4, during flagellogenesis. Hence, DNALI1 may possess a non-classical molecular function, whereby it regulates the cytoplasmic dynein complex that assembles the flagella. We conclude that a DNALI deficiency-induced IDAs injury and an asymmetric FS-driven tail rigid structure alteration may simultaneously cause flagellum immotility. Finally, intracytoplasmic sperm injection (ICSI) can effectively resolve patient infertility. Collectively, we demonstrate that DNALI1 is a newly causative gene for AZS in both humans and mice, which possesses multiple crucial roles in modulating flagellar assembly and motility.

The Male Mouse Meiotic Cilium Emanates from the Mother Centriole at Zygotene Prior to Centrosome Duplication

Cilia are hair-like projections of the plasma membrane with an inner microtubule skeleton known as axoneme. Motile cilia and flagella beat to displace extracellular fluids, playing important roles in the airways and reproductive system. On the contrary, primary cilia function as cell-type-dependent sensory organelles, detecting chemical, mechanical, or optical signals from the extracellular environment. Cilia dysfunction is associated with genetic diseases called ciliopathies and with some types of cancer. Cilia have been recently identified in zebrafish gametogenesis as an important regulator of bouquet conformation and recombination. However, there is little information about the structure and functions of cilia in mammalian meiosis. Here we describe the presence of cilia in male mouse meiotic cells. These solitary cilia formed transiently in 20% of zygotene spermatocytes and reached considerable lengths (up to 15-23 µm). CEP164 and CETN3 localization studies indicated that these cilia emanate from the mother centriole prior to centrosome duplication. In addition, the study of telomeric TFR2 suggested that cilia are not directly related to the bouquet conformation during early male mouse meiosis. Instead, based on TEX14 labeling of intercellular bridges in spermatocyte cysts, we suggest that mouse meiotic cilia may have sensory roles affecting cyst function during prophase I.

The Role of Primary Cilia-Associated Phosphoinositide Signaling in Development

Primary cilia are microtube-based organelles that extend from the cell surface and function as biochemical and mechanical extracellular signal sensors. Primary cilia coordinate a series of signaling pathways during development. Cilia dysfunction leads to a pleiotropic group of developmental disorders, termed ciliopathy. Phosphoinositides (PIs), a group of signaling phospholipids, play a crucial role in development and tissue homeostasis by regulating membrane trafficking, cytoskeleton reorganization, and organelle identity. Accumulating evidence implicates the involvement of PI species in ciliary defects and ciliopathies. The abundance and localization of PIs in the cell are tightly regulated by the opposing actions of kinases and phosphatases, some of which are recently discovered in the context of primary cilia. Here, we review several cilium-associated PI kinases and phosphatases, including their localization along cilia, function in regulating the ciliary biology under normal conditions, as well as the connection of their disease-associated mutations with ciliopathies.

Perfluorooctanesulfonic acid exposure altered hypothalamic metabolism and disturbed male fecundity

Previous studies have examined the effects of perfluorooctanesulfonic acid (PFOS) on disruption of the blood-testis barrier and spermatogenesis. Sertoli and Leydig cells were perturbed, resulting in a decrease in testosterone levels and sperm counts. However, the effects of PFOS on male fecundity are not limited to the testes. In this study, we demonstrated that oral PFOS exposure (1 μg/g BW and 5 μg/g BW) decreased the function of the Luteinizing hormone (LH)/Luteinizing hormone receptor (LHr) and decreased epididymal sperm motility. Consistently, testicular transcriptome analysis revealed that PFOS altered the expression of a cluster of genes associated with sperm motility and steroidogenesis. In mice exposed to PFOS, c-Fos immunostaining showed activation of the lateral septal nucleus (LS), paraventricular thalamus (PVT), locus coeruleus (LC), which are known to be related to anxiety-like behaviors. Metabolomic analyses of the hypothalamus revealed that exposure to PFOS perturbed the translation of proteins, as well as the biosynthesis of neurotransmitters and neuromodulators. Altogether, the activation of brain nuclei, shift of hypothalamic metabolome, and reduction of LH/LHr circuit resulted from PFOS exposure suggested the toxicant's systematic effects on male reproduction.

Self-sustained three-dimensional beating of a model eukaryotic flagellum

Flagella and cilia are common features of a wide variety of biological cells and play important roles in locomotion and feeding at the microscale. The beating of flagella is controlled by molecular motors that exert forces along the length of the flagellum and are regulated by a feedback mechanism coupled to the flagella deformation. We develop a three-dimensional (3D) flagellum beating model based on sliding-controlled motor feedback, accounting for both bending and twist, as well as differential bending resistances along and orthogonal to the major bending plane of the flagellum. We show that beating is generated and sustained spontaneously for a sufficiently high motor activity through an instability mechanism. Isotropic bending rigidities in the flagellum lead to 3D helical beating patterns. By contrast, anisotropic flagella present a rich variety of wave-like beating dynamics, including both 3D beating patterns as well as planar beating patterns. We show that the ability to generate nearly planar beating despite the 3D beating machinery requires only a modest degree of bending anisotropy, and is a feature observed in many eukaryotic flagella such as mammalian spermatozoa.

Consensus nomenclature for dyneins and associated assembly factors

Dyneins are highly complex, multicomponent, microtubule-based molecular motors. These enzymes are responsible for numerous motile behaviors in cytoplasm, mediate retrograde intraflagellar transport (IFT), and power ciliary and flagellar motility. Variants in multiple genes encoding dyneins, outer dynein arm (ODA) docking complex subunits, and cytoplasmic factors involved in axonemal dynein preassembly (DNAAFs) are associated with human ciliopathies and are of clinical interest. Therefore, clear communication within this field is particularly important. Standardizing gene nomenclature, and basing it on orthology where possible, facilitates discussion and genetic comparison across species. Here, we discuss how the human gene nomenclature for dyneins, ODA docking complex subunits, and DNAAFs has been updated to be more functionally informative and consistent with that of the unicellular green alga Chlamydomonas reinhardtii, a key model organism for studying dyneins and ciliary function. We also detail additional nomenclature updates for vertebrate-specific genes that encode dynein chains and other proteins involved in dynein complex assembly.

Mitochondrial regulation during male germ cell development

Mitochondria tailor their morphology to execute their specialized functions in different cell types and/or different environments. During spermatogenesis, mitochondria undergo continuous morphological and distributional changes with germ cell development. Deficiencies in these processes lead to mitochondrial dysfunction and abnormal spermatogenesis, thereby causing male infertility. In recent years, mitochondria have attracted considerable attention because of their unique role in the regulation of piRNA biogenesis in male germ cells. In this review, we describe the varied characters of mitochondria and focus on key mitochondrial factors that play pivotal roles in the regulation of spermatogenesis, from primordial germ cells to spermatozoa, especially concerning metabolic shift, stemness and reprogramming, mitochondrial transformation and rearrangement, and mitochondrial defects in human sperm. Further, we discuss the molecular mechanisms underlying these processes.

In Silico Analysis of CatSper Family Genes and APOB Gene Regulation in Male Infertility

Sperm concentration and sperm motility are the two major causes of male infertility. Having spermatozoa in semen without motility or flagellum tail defect is a major concern needed to be investigated. The CatSper genes are the novel family of four sperm-specific Ca²⁺-permeable channels which plays an important role in sperm motility, acrosome reaction, sperm, and oocyte fusion. CatSper1, CatSper2, and CatSper3 are very well-studied genes for their role in asthenozoospermia, but the association of these genes with metabolic genes is still unstudied. Another unrevealed aspect is how ROS alter the function of CatSper genes. Among the Catsper family genes, the role of CatSper4 gene must be explored more. In this study, we have used the in silico approach to find the connection between the CatSper family gene with glycolytic genes and also the involvement of CATSPER4 protein in sperm flagellum using the STRING database. Connection of CATSPER1 protein with lipid metabolic gene is also found in Reactome database, and after that gene ontology of these genes was done by using DAVID and Enrichr databases. This analysis showed a strong interaction between CATSPER1, CATSPER2, and CATSPER3 protein with glycolytic protein (i.e., GAPDHS and PGK2), and CATSPER4 protein shows strong relation in the function of sperm flagellum. We also found a novel gene, i.e., APOB contributing to sperm motility. Gene ontology showed the role of APOB and glycolytic proteins in sperm motility. Enrichr analysis showed the association of APOB and glycolytic proteins in asthenozoospermia and CATSPER4 protein with sperm flagellum. Elsevier Pathway Collection also showed proteins involved in male infertility (i.e., GAPDHS). Therefore, we report the role of the CatSper4 gene in sperm tail function and the APOB novel gene involved in sperm motility. Understanding the molecular mechanism(s) of regulations of the CatSper family gene will help us to develop new therapeutic approaches in infertile males.

Homozygous mutation in DNALI1 leads to asthenoteratozoospermia by affecting the inner dynein arms

Asthenozoospermia is the most common cause of male infertility. Dynein protein arms play a crucial role in the motility of sperm flagella and defects in these proteins generally impair the axoneme structure and affect sperm flagella function. In this study, we performed whole exome sequencing for a cohort of 126 infertile patients with asthenozoospermia and identified homozygous DNALI1 mutation in one patient from a consanguineous family. This identified homozygous mutation was verified by Sanger sequencing. In silico analysis showed that this homozygous mutation is very rare, highly pathogenic, and very conserved. Sperm routine analysis confirmed that the motility of the spermatozoa from the patient significantly decreased. Further sperm morphology analysis showed that the spermatozoa from the patient exhibited multiple flagella morphological defects and a specific loss in the inner dynein arms. Fortunately, the patient was able to have his child via intracytoplasmic sperm injection treatment. Our study is the first to demonstrate that homozygous DNALI1 mutation may impair the integration of axoneme structure, affect sperm motility and cause asthenoteratozoospermia in human beings.

The flagellar germ-line hypothesis: How flagellate and ciliate gametes significantly shaped the evolution of organismal complexity

This essay presents a hypothesis which contends that the development of organismic complexity in the eukaryotes depended extensively on propagation via flagellated and ciliated gametes. Organisms utilizing flagellate and ciliate gametes to propagate their germ line have contributed most of the organismic complexity found in the higher animals. The genes of the flagellum and the flagellar assembly system (intraflagellar transport) have played a disproportionately important role in the construction of complex tissues and organs. The hypothesis also proposes that competition between large numbers of haploid flagellated male gametes rigorously conserved the functionality of a key set of flagellar genes for more than 700 million years. This in turn has insured that a large set (>600) of highly functional cytoskeletal and signal pathway genes is always present in the lineage of organisms with flagellated or ciliated gametes to act as a dependable resource, or "toolkit," for organ elaboration.

CCDC40 mutation as a cause of infertility in a Chinese family with primary ciliary dyskinesia

TRIAL DESIGN

Primary ciliary dyskinesia (PCD) is a genetical disease that inherited in an autosomal-recessive way. Its clinical manifestations (such as male infertility) are mainly caused by defects of motion-related cilia that encoded by mutated genes. Although some mutation has been verified, a number of mutations of PCD remain elusive. The main purpose of this study is to identify mutant genes in a Chinese family with PCD, and to verify the safety and effectiveness of intracytoplasmic sperm injection (ICSI) of infertility caused by PCD.

METHODS

Imaging examination was used to exclude pulmonary inflammation and visceral translocation. Semen analysis was used to assess the quality of the proband's sperm. Transmission electron microscopy (TEM) was conducted to assess the ultrastructure of flagella and cilia. Targeted next generation sequencing and Sanger sequencing and qPCR (real-time quantitative polymerase chain reaction detecting system) were applied to identified mutation of Chinese Family suspected of having PCD. Viable sperm were selected by hypo-osmotic swelling test (HOST) for ICSI.

RESULTS

We report 2 novel mutations in CCDC40 gene (c.1259delA and EX17_20 deletion) resulted in immobility of sperm and infertility of the proband. These mutations were confirmed in the proband's sister (heterozygous) and his parents (recessive carrier) by Sanger sequencing and qPCR. All the spermatozoa from the proband were immotile. Ultrastructural defects were found in flagella and cilia of proband and his sister. Viable sperms were selected by HOST for ICSI and fertilized 9 of 21 eggs. Two frozen embryos were transplanted and a healthy 3500 g boy was delivered at 40 + 4 weeks' gestation. And then, we summarized the genes related to PCD and the mutant sites of CCDC40 gene.

CONCLUSION

We reported 2 novel mutants in CCDC40 gene (c.1259delA and EX17_20 deletion), which could be candidates for genetic diagnosis in PCD patients. The combination of targeted next generation sequencing and Sanger sequencing may be a useful tool to diagnose PCD. ICSI is a considerable method in treatment of infertility caused by PCD.

KIF3B gene silent variant leading to sperm morphology and motility defects and male infertility

Sperm structural and functional defects are leading causes of male infertility. Patients with immotile sperm disorders suffer from axoneme failure and show a significant reduction in sperm count. The kinesin family member 3B (KIF3B) is one of the genes involved in the proper formation of sperm with a critical role in intraflagellar and intramanchette transport. A part of exon 2 and exons 3–5 of the KIF3B encodes a protein coiled-coil domain that interacts with IFT20 from the IFT protein complex. In the present study, the coding region of KIF3B coiled-coil domain was assessed in 88 oligoasthenoteratozoospermic patients, and the protein expression was evaluated in the mature spermatozoa of the case and control groups using immunocytochemistry and western blotting. According to the results, there was no genetic variation in the exons 3–5 of the KIF3B, but a new A &gt; T variant was identified within the exon 2 in 30 patients, where nothing was detected in the control group. In contrast to healthy individuals, significantly reduced protein expression was observable in oligoasthenoteratozoospermic (OAT) patients carrying variation where protein organization was disarranged, especially in the principal piece and midpiece of the sperm tail. Besides, the protein expression level was lower in the patients’ samples compared to that of the control group. According to the results of the present study the NM_004798.3:c.1032A &gt; T, p.Pro344 = variant; which has been recently submitted to the Clinvar database; although synonymous, causes alterations in the transcription factor binding site, exon skipping, and also exonic splicing enhancer-binding site. Therefore, KIF3B can play an important role in spermatogenesis and the related protein reduction can cause male infertility.

Ultrastructural and Functional Analysis of a Novel Extra-Axonemal Structure in Parasitic Trichomonads

Trichomonas vaginalis and Tritrichomonas foetus are extracellular flagellated parasites that inhabit humans and other mammals, respectively. In addition to motility, flagella act in a variety of biological processes in different cell types, and extra-axonemal structures (EASs) have been described as fibrillar structures that provide mechanical support and act as metabolic, homeostatic, and sensory platforms in many organisms. It has been assumed that T. vaginalis and T. foetus do not have EASs. However, here, we used complementary electron microscopy techniques to reveal the ultrastructure of EASs in both parasites. Such EASs are thin filaments (3-5 nm diameter) running longitudinally along the axonemes and surrounded by the flagellar membrane, forming prominent flagellar swellings. We observed that the formation of EAS increases after parasite adhesion on the host cells, fibronectin, and precationized surfaces. A high number of rosettes, clusters of intramembrane particles that have been proposed as sensorial structures, and microvesicles protruding from the membrane were observed in the EASs. Our observations demonstrate that T. vaginalis and T. foetus can connect to themselves by EASs present in flagella. The protein VPS32, a member of the ESCRT-III complex crucial for diverse membrane remodeling events, the pinching off and release of microvesicles, was found in the surface as well as in microvesicles protruding from EASs. Moreover, we demonstrated that the formation of EAS also increases in parasites overexpressing VPS32 and that T. vaginalis-VPS32 parasites showed greater motility in semisolid agar. These results provide valuable data about the role of the flagellar EASs in the cell-to-cell communication and pathogenesis of these extracellular parasites.

Bi-allelic mutations of DNAH10 cause primary male infertility with asthenoteratozoospermia in humans and mice

Multiple morphological abnormalities of the sperm flagella (MMAF)-induced asthenoteratozoospermia is a common cause of male infertility. Previous studies have identified several MMAF-associated genes, highlighting the condition's genetic heterogeneity. To further define the genetic causes underlying MMAF, we performed whole-exome sequencing in a cohort of 643 Chinese MMAF-affected men. Bi-allelic DNAH10 variants were identified in five individuals with MMAF from four unrelated families. These variants were either rare or absent in public population genome databases and were predicted to be deleterious by multiple bioinformatics tools. Morphological and ultrastructural analyses of the spermatozoa obtained from men harboring bi-allelic DNAH10 variants revealed striking flagellar defects with the absence of inner dynein arms (IDAs). DNAH10 encodes an axonemal IDA heavy chain component that is predominantly expressed in the testes. Immunostaining analysis indicated that DNAH10 localized to the entire sperm flagellum of control spermatozoa. In contrast, spermatozoa from the men harboring bi-allelic DNAH10 variants exhibited an absence or markedly reduced staining intensity of DNAH10 and other IDA components, including DNAH2 and DNAH6. Furthermore, the phenotypes were recapitulated in mouse models lacking Dnah10 or expressing a disease-associated variant, confirming the involvement of DNAH10 in human MMAF. Altogether, our findings in humans and mice demonstrate that DNAH10 is essential for sperm flagellar assembly and that deleterious bi-allelic DNAH10 variants can cause male infertility with MMAF. These findings will provide guidance for genetic counseling and insights into the diagnosis of MMAF-associated asthenoteratozoospermia.

Structure of the trypanosome paraflagellar rod and insights into non-planar motility of eukaryotic cells

Eukaryotic flagella (synonymous with cilia) rely on a microtubule-based axoneme, together with accessory filaments to carryout motility and signaling functions. While axoneme structures are well characterized, 3D ultrastructure of accessory filaments and their axoneme interface are mostly unknown, presenting a critical gap in understanding structural foundations of eukaryotic flagella. In the flagellum of the protozoan parasite Trypanosoma brucei (T. brucei), the axoneme is accompanied by a paraflagellar rod (PFR) that supports non-planar motility and signaling necessary for disease transmission and pathogenesis. Here, we employed cryogenic electron tomography (cryoET) with sub-tomographic averaging, to obtain structures of the PFR, PFR-axoneme connectors (PACs), and the axonemal central pair complex (CPC). The structures resolve how the 8 nm repeat of the axonemal tubulin dimer interfaces with the 54 nm repeat of the PFR, which consist of proximal, intermediate, and distal zones. In the distal zone, stacked "density scissors" connect with one another to form a "scissors stack network (SSN)" plane oriented 45° to the axoneme axis; and ~370 parallel SSN planes are connected by helix-rich wires into a paracrystalline array with ~90% empty space. Connections from these wires to the intermediate zone, then to overlapping layers of the proximal zone and to the PACs, and ultimately to the CPC, point to a contiguous pathway for signal transmission. Together, our findings provide insights into flagellum-driven, non-planar helical motility of T. brucei and have broad implications ranging from cell motility and tensegrity in biology, to engineering principles in bionics.

The effects of Vitamin D3 supplementation on Spermatogram and endocrine factors in asthenozoospermia infertile men: a randomized, triple blind, placebo-controlled clinical trial

OBJECTIVE

Evaluate the effects of vitamin D3 (VD3) on sperm parameters and endocrine markers in infertile men with asthenozoospermia.

MATERIALS AND METHODS

This randomized, triple-masking, placebo-controlled clinical trial conducted on 86 asthenozoospermia infertile men with serum 25 hydroxy vitamin D3 (25(OH)VD3) < 30 ng/ml in the infertility clinic of Ahvaz Jahad daneshgahi, Iran. Patients were randomly allocated to groups A and B, who received daily 4000 IU VD3 and matching placebo respectively for 3 months. Demographic data, dietary intake, physical activity, sun exposure, anthropometric indices, serum 25(OH)VD3, luteinizing hormone (LH), follicle-stimulating hormone (FSH), total testosterone (T), estradiol (E2),, sex hormone-binding globulin (SHBG), free androgen index (FAI = T/SHBG. 100), T/LH and T/E2 ratios, prolactin (PRO), parathyroid hormone (PTH), osteocalcin (OCN), phosphorus and sperm parameters were assessed.

RESULTS

Three months VD3 supplementation with 4000 IU/day had no significant effects body weight, body mass index (BMI), waist circumference (WC), body fat (BF), serum, OCN, LH, FSH, T, E2, SHBG, PRO, T/E2 ratio, FAI, semen volume, sperm count and normal sperm morphology. It increases serum 25(OH)VD3, PTH and phosphorus and seminal and serum calcium, T/LH ratio and total and progressive sperm motility and decreased significantly compared to the baseline and placebo group.

CONCLUSION

VD3 supplementation may affect sperm motility in men with asthenozoospermia and serum 25(OH)VD3 < 30 ng/ml.

TRIAL REGISTRATION

Iran Clinical Trials Registry, ID: IRCT20151128025274N4, registered on 28 March 2018, URL of trial registry record: https://www.irct.ir/trial/29983.

Insight on multiple morphological abnormalities of sperm flagella in male infertility: what is new?

The syndrome of multiple morphological abnormalities of the sperm flagella (MMAF) is a specific kind of asthenoteratozoospermia with a mosaic of flagellar morphological abnormalities (absent, short, bent, coiled, and irregular flagella). MMAF was proposed in 2014 and has attracted increasing attention; however, it has not been clearly understood. In this review, we elucidate the definition of MMAF from a systematical view, the difference between MMAF and other conditions with asthenoteratozoospermia or asthenozoospermia (such as primary mitochondrial sheath defects and primary ciliary dyskinesia), the knowledge regarding its etiological mechanism and related genetic findings, and the clinical significance of MMAF for intracytoplasmic sperm injection and genetic counseling. This review provides the basic knowledge for MMAF and puts forward some suggestions for further investigations.

Limitations and opportunities in the pharmacotherapy of ciliopathies

Ciliopathies are a family of rather diverse conditions, which have been grouped based on the finding of altered or dysfunctional cilia, potentially motile, small cellular antennae extending from the surface of postmitotic cells. Cilia-related disorders include embryonically arising conditions such as Joubert, Usher or Kartagener syndrome, but also afflictions with a postnatal or even adult onset phenotype, i.e. autosomal dominant polycystic kidney disease. The majority of ciliopathies are syndromic rather than affecting only a single organ due to cilia being found on almost any cell in the human body. Overall ciliopathies are considered rare diseases. Despite that, pharmacological research and the strive to help these patients has led to enormous therapeutic advances in the last decade. In this review we discuss new treatment options for certain ciliopathies, give an outlook on promising future therapeutic strategies, but also highlight the limitations in the development of therapeutic approaches of ciliopathies.

Central Apparatus, the Molecular Kickstarter of Ciliary and Flagellar Nanomachines

Motile cilia and homologous organelles, the flagella, are an early evolutionarily invention, enabling primitive eukaryotic cells to survive and reproduce. In animals, cilia have undergone functional and structural speciation giving raise to typical motile cilia, motile nodal cilia, and sensory immotile cilia. In contrast to other cilia types, typical motile cilia are able to beat in complex, two-phase movements. Moreover, they contain many additional structures, including central apparatus, composed of two single microtubules connected by a bridge-like structure and assembling numerous complexes called projections. A growing body of evidence supports the important role of the central apparatus in the generation and regulation of the motile cilia movement. Here we review data concerning the central apparatus structure, protein composition, and the significance of its components in ciliary beating regulation.

Genetic mutations contributing to non-obstructive azoospermia

Non-obstructive azoospermia is a distinct diagnosis within male infertility in which no sperm is found in the ejaculate as a result of spermatogenesis failure. Because of the increased prevalence of genetic abnormalities in men with non-obstructive azoospermia, male infertility guidelines recommend screening for karyotype abnormalities and Y chromosome microdeletions in this population. Numerous karyotype abnormalities may be present resulting in impaired spermatogenesis, including: Klinefelter syndrome, translocations, and deletions. Y chromosome microdeletions of the AZFa, AZFb, AZFc subregions all can also result in non-obstructive azoospermia with the possibility of sperm being present if only the AZFc subregion is deleted. While these are the two genetic tests recommended by the guidelines, nearly 50%-80% of non-obstructive azoospermia has no identifiable cause and is deemed idiopathic. Several other genetic defects can lead to non-obstructive azoospermia including Kallmann syndrome, mild androgen insensitivity syndrome, and TEX11. While many additional candidate genes have been proposed, many have yet to be verified or are so infrequent in the population that screening is cost-ineffective. Much research is still required in the genetics of non-obstructive azoospermia and will require multi-institutional initiatives to better understand the genetics of condition.

The anatomy, movement, and functions of human sperm tail: an evolving mystery

Sperms have attracted attention of many researchers since it was discovered by Antonie van Leeuwenhoek in 1677. Though a small cell, its every part has complex structure and different function to play in carrying life. Sperm tail is most complicated structure with more than 1000 proteins involved in its functioning. With the advent of three-dimensional microscopes, many studies are undergoing to understand exact mechanism of sperm tail movement. Most recent studies have shown that sperms move by spinning rather than swimming. Each subunit of tail, including axonemal, peri-axonemal structures, plays essential roles in sperm motility, capacitation, hyperactivation, fertilization. Furthermore, over 2300 genes are involved in spermatogenesis. A number of genetic mutations have been linked with abnormal sperm flagellar development leading to motility defects and male infertility. It was found that 6% of male infertility cases are related to genetic causes, and 4% of couples undergoing intracytoplasmic sperm injection for male subfertility have chromosomal abnormalities. Hence, an understanding of sperm tail development and genes associated with its normal functioning can help in better diagnosis of male infertility and its management. There is still a lot that needs to be discovered about genes, proteins contributing to normal human sperm tail development, movement, and role in male fertility. Sperm tail has complex anatomy, with surrounding axoneme having 9 + 2 microtubules arrangement along its entire length and peri-axonemal structures that contribute in sperm motility and fertilization. In future sperm tail-associated genes, proteins and subunits can be used as markers of male fertility.

Ultrastructural Sperm Flagellum Defects in a Patient With CCDC39 Compound Heterozygous Mutations and Primary Ciliary Dyskinesia/Situs Viscerum Inversus

Introduction: Primary ciliary dyskinesia (PCD) is a rare autosomal recessive disease characterized by structural or functional motile cilia abnormalities. Up to 40 different genes seem, at the moment, to be involved in the pathogenesis of PCD. A number of ultrastructural defects have also been reported in sperm flagella, but the sperm mitochondrial membrane potential (MMP) has never been described in these cases.

Aim: The aim of this study was to report the sperm MMP and ultrastructural abnormalities of the sperm flagella found in a patient with PCD and situs inversus (Kartagener syndrome) and its characterization from the genetic point of view.

Methods: Transmission electronic microscopy (TEM) analysis was used to evaluate flagella ultrastructure. The genetic testing was performed by next-generation sequencing. Sperm DNA fragmentation and MMP were also evaluated by flow cytometry.

Results: We report here the case of an 18-year-old male patient with PCD and situs inversus and severe oligo-astheno-teratozoospermia. TEM analysis of his spermatozoa showed an abnormal connecting piece. The mid piece appeared abnormally thickened, with cytoplasmic residue, dysplasia of fibrous sheath, loss of the outer dynein arms (ODAs), truncated inner dynein arms, and supernumerary outer fibers. The percentage of spermatozoa with fragmented DNA was normal, whereas a high percentage of spermatozoa had low MMP, suggesting an altered mitochondrial function. The genetic analysis showed the presence of c.610-2A > G, p.Arg811Cys compound heterozygous mutations in the CCDC39 gene.

Conclusion: The case herein reported suggests that the high percentage of sperm with low MMP may play a role in the pathogenesis of asthenozoospermia in patients with Kartagener syndrome. In addition, we report, for the first time, the missense variant p.Arg811Cys in the CCDC39 gene in a patient with Kartagener syndrome. Although in silico analysis predicts its damaging potential, its clinical meaning remains unclear.

Cilium axoneme internalization and degradation in chytrid fungi

Loss of the cilium is important for cell cycle progression and certain developmental transitions. Chytrid fungi are a group of basal fungi that have retained centrioles and cilia, and they can disassemble their cilia via axoneme internalization as part of the transition from free-swimming spores to sessile sporangia. While this type of cilium disassembly has been observed in many single-celled eukaryotes, it has not been well characterized because it is not observed in common model organisms. To better characterize cilium disassembly via axoneme internalization, we focused on chytrids Rhizoclosmatium globosum and Spizellomyces punctatus to represent two lineages of chytrids with different motility characteristics. Our results show that each chytrid species can reel in its axoneme into the cell body along its cortex on the order of minutes, while S. punctatus has additional faster ciliary compartment loss and lash-around mechanisms. S. punctatus retraction can also occur away from the cell cortex and is partially actin dependent. Post-internalization, the tubulin of the axoneme is degraded in both chytrids over the course of about 2 hr. Axoneme disassembly and axonemal tubulin degradation are both partially proteasome dependent. Overall, chytrid cilium disassembly is a fast process that separates axoneme internalization and degradation.

The Genetic Architecture of Post-Zygotic Reproductive Isolation Between Anopheles coluzzii and An. quadriannulatus

The Anopheles gambiae complex is comprised of eight morphologically indistinguishable species and has emerged as a model system for the study of speciation genetics due to the rapid radiation of its member species over the past two million years. Male hybrids between most An. gambiae complex species pairs are sterile, and some genotype combinations in hybrid males cause inviability. We investigated the genetic basis of hybrid male inviability and sterility between An. coluzzii and An. quadriannulatus by measuring segregation distortion and performing a QTL analysis of sterility in a backcross population. Hybrid males were inviable if they inherited the An. coluzzii X chromosome and were homozygous at one or more loci in 18.9 Mb region of chromosome 3. The An. coluzzii X chromosome has a disproportionately large effect on hybrid sterility when introgressed into an An. quadriannulatus genetic background. Additionally, an epistatic interaction between the An. coluzzii X and a 1.12 Mb, pericentric region of the An. quadriannulatus 3L chromosome arm has a statistically significant contribution to the hybrid sterility phenotype. This same epistatic interaction occurs when the An. coluzzii X is introgressed into the genetic background of An. arabiensis, the sister species of An. quadriannulatus, suggesting that this may represent one of the first Dobzhansky-Muller incompatibilities to evolve early in the radiation of the Anopheles gambiae species complex. We describe the additive effects of each sterility QTL, epistatic interactions between them, and genes within QTL with protein functions related to mating behavior, reproduction, spermatogenesis, and microtubule morphogenesis, whose divergence may contribute to post-zygotic reproductive isolation between An. coluzzii and An. quadriannulatus.

Epb41l5 interacts with Iqcb1 and regulates ciliary function in zebrafish embryos

Erythrocyte protein band 4.1 like 5 (EPB41L5) is an adaptor protein beneath the plasma membrane that functions to control epithelial morphogenesis. Here we report a previously uncharacterized role of EPB41L5 in controlling ciliary function. We found that EPB41L5 forms a complex with IQCB1 (previously known as NPHP5), a ciliopathy protein. Overexpression of EPB41L5 reduced IQCB1 localization at the ciliary base in cultured mammalian epithelial cells. Conversely, epb41l5 knockdown increased IQCB1 localization at the ciliary base. epb41l5-deficient zebrafish embryos or embryos expressing C-terminally modified forms of Epb41l5 developed cilia with reduced motility and exhibited left-right patterning defects, an outcome of abnormal ciliary function. We observed genetic synergy between epb41l5 and iqcb1. Moreover, EPB41L5 decreased IQCB1 interaction with CEP290, another ciliopathy protein and a component of the ciliary base and centrosome. Together, these observations suggest that EPB41L5 regulates the composition of the ciliary base and centrosome through IQCB1 and CEP290.

Analysis of the sperm flagellar axoneme using gene-modified mice

Infertility is a global health issue that affects 1 in 6 couples, with male factors contributing to 50% of cases. The flagellar axoneme is a motility apparatus of spermatozoa, and disruption of its structure or function could lead to male infertility. The axoneme consists of a "9+2" structure that contains a central pair of two singlet microtubules surrounded by nine doublet microtubules, in addition to several macromolecular complexes such as dynein arms, radial spokes, and nexin-dynein regulatory complexes. Molecular components of the flagellar axoneme are evolutionally conserved from unicellular flagellates to mammals, including mice. Although knockout (KO) mice have been generated to understand their function in the formation and motility regulation of sperm flagella, the majority of KO mice die before sexual maturation due to impaired ciliary motility, which makes it challenging to analyze mature spermatozoa. In this review, we introduce methods that have been used to overcome premature lethality, focusing on KO mouse lines of central pair components.

Microtubule Organization in Striated Muscle Cells

Distinctly organized microtubule networks contribute to the function of differentiated cell types such as neurons, epithelial cells, skeletal myotubes, and cardiomyocytes. In striated (i.e., skeletal and cardiac) muscle cells, the nuclear envelope acts as the dominant microtubule-organizing center (MTOC) and the function of the centrosome—the canonical MTOC of mammalian cells—is attenuated, a common feature of differentiated cell types. We summarize the mechanisms known to underlie MTOC formation at the nuclear envelope, discuss the significance of the nuclear envelope MTOC for muscle function and cell cycle progression, and outline potential mechanisms of centrosome attenuation.

Dynein assembly factor with WD repeat domains 1 (DAW1) is required for the function of motile cilia in the planarian Schmidtea mediterranea

Motile cilia propel directed cell movements and sweep fluids across the surface of tissues. Orthologs of Dynein Assembly Factor with WD Repeat Domains 1 (DAW1) support normal ciliary beating by enhancing delivery of dynein complexes to axonemal microtubules. DAW1 mutations in vertebrates result in multiple developmental abnormalities and early or prenatal lethality, complicating functional assessment of DAW1 in adult structures. Planarian flatworms maintain cellular homeostasis and regenerate through differentiation of adult pluripotent stem cells, and systemic RNA-interference (RNAi) can be induced to analyze gene function at any point after birth. A single ortholog of DAW1 was identified in the genome of the planarian Schmidtea mediterranea (Smed-daw1). Smed-DAW1 is composed of eight WD repeats, which are 55% identical to the founding member of this protein family (Chlamydomonas reinhardtii ODA16) and 58% identical to human DAW1. Smed-daw1 is expressed in the planarian epidermis, protonephridial excretory system, and testes, all of which contain cells functionally dependent on motile cilia. Smed-daw1 RNAi resulted in locomotion defects and edema, which are phenotypes characteristic of multiciliated epidermis and protonephridial dysfunction, respectively. Changes in abundance or length of motile cilia were not observed at the onset of phenotypic manifestations upon Smed-daw1 RNAi, corroborating with studies showing that DAW-1 loss of function leads to aberrant movement of motile cilia in other organisms, rather than loss of cilia per se. However, extended RNAi treatments did result in shorter epidermal cilia and decreased abundance of ciliated protonephridia, suggesting that Smed-daw1 is required for homeostatic maintenance of these structures in flatworms.

The tubulin code and its role in controlling microtubule properties and functions

Microtubules are core components of the eukaryotic cytoskeleton with essential roles in cell division, shaping, motility and intracellular transport. Despite their functional heterogeneity, microtubules have a highly conserved structure made from almost identical molecular building blocks: the tubulin proteins. Alternative tubulin isotypes and a variety of post-translational modifications control the properties and functions of the microtubule cytoskeleton, a concept known as the 'tubulin code'. Here we review the current understanding of the molecular components of the tubulin code and how they impact microtubule properties and functions. We discuss how tubulin isotypes and post-translational modifications control microtubule behaviour at the molecular level and how this translates into physiological functions at the cellular and organism levels. We then go on to show how fine-tuning of microtubule function by some tubulin modifications can affect homeostasis and how perturbation of this fine-tuning can lead to a range of dysfunctions, many of which are linked to human disease.

Molecular Changes Induced by Oxidative Stress that Impair Human Sperm Motility

A state of oxidative stress (OS) and the presence of reactive oxygen species (ROS) in the male reproductive tract are strongly correlated with infertility. While physiological levels of ROS are necessary for normal sperm functioning, elevated ROS production can overwhelm the cell's limited antioxidant defenses leading to dysfunction and loss of fertilizing potential. Among the deleterious pleiotropic impacts arising from OS, sperm motility appears to be particularly vulnerable. Here, we present a mechanistic account for how OS contributes to altered sperm motility profiles. In our model, it is suggested that the abundant polyunsaturated fatty acids (PUFAs) residing in the sperm membrane serve to sensitize the male germ cell to ROS attack by virtue of their ability to act as substrates for lipid peroxidation (LPO) cascades. Upon initiation, LPO leads to dramatic remodeling of the composition and biophysical properties of sperm membranes and, in the case of the mitochondria, this manifests in a dissipation of membrane potential, electron leakage, increased ROS production and reduced capacity for energy production. This situation is exacerbated by the production of cytotoxic LPO byproducts such as 4-hydroxynonenal, which dysregulate molecules associated with sperm bioenergetic pathways as well as the structural and signaling components of the motility apparatus. The impact of ROS also extends to lesions in the paternal genome, as is commonly seen in the defective spermatozoa of asthenozoospermic males. Concluding, the presence of OS in the male reproductive tract is strongly and positively correlated with reduced sperm motility and fertilizing potential, thus providing a rational target for the development of new therapeutic interventions.

Novel mutations in SPEF2 causing different defects between flagella and cilia bridge: the phenotypic link between MMAF and PCD

Severe asthenozoospermia is a common cause of male infertility. Recent studies have revealed that SPEF2 mutations lead to multiple morphological abnormalities of the sperm flagella (MMAF) without primary ciliary dyskinesia (PCD) symptoms in males, but PCD phenotype was also found in one female individual. Therefore, whether there is a phenotypic continuum ranging from infertile patients with PCD to MMAF patients with no or low noise PCD manifestations remains elusive. Here, we performed whole-exome sequencing in 47 patients with severe asthenozoospermia from 45 unrelated Chinese families. We identified four novel biallelic mutations in SPEF2 (8.9%, 4/45) in six affected individuals (12.8%, 6/47), while no deleterious biallelic variants in SPEF2 were detected in 637 controls, including 219 with oligoasthenospermia, 195 with non-obstructive azoospermia, and 223 fertile controls. Notably, all six patients exhibited PCD-like symptoms, including recurrent airway infections, bronchitis, and rhinosinusitis. Ultrastructural analysis revealed normal 9 + 2 axonemes of respiratory cilia but consistently abnormal 9 + 0 axoneme or disordered accessory structures of sperm flagella, indicating different roles of SPEF2 in sperm flagella and respiratory cilia. Subsequently, a Spef2 knockout mouse model was used to validate the PCD-like phenotype and male infertility, where the subfertility of female Spef2^-/- mice was found unexpectedly. Overall, our data bridge the link between MMAF and PCD based on the association of SPEF2 mutations with both infertility and PCD in males and provide basis for further exploring the molecular mechanism of SPEF2 during spermiogenesis and ciliogenesis.

The genetic architecture of morphological abnormalities of the sperm tail

Spermatozoa contain highly specialized structural features reflecting unique functions required for fertilization. Among them, the flagellum is a sperm-specific organelle required to generate the motility, which is essential to reach the egg. The flagellum integrity is, therefore, critical for normal sperm function and flagellum defects consistently lead to male infertility due to reduced or absent sperm motility defined as asthenozoospermia. Multiple morphological abnormalities of the flagella (MMAF), also called short tails, is among the most severe forms of sperm flagellum defects responsible for male infertility and is characterized by the presence in the ejaculate of spermatozoa being short, coiled, absent and of irregular caliber. Recent studies have demonstrated that MMAF is genetically heterogeneous which is consistent with the large number of proteins (over one thousand) localized in the human sperm flagella. In the past 5 years, genomic investigation of the MMAF phenotype allowed the identification of 18 genes whose mutations induce MMAF and infertility. Here we will review information about those genes including their expression pattern, the features of the encoded proteins together with their localization within the different flagellar protein complexes (axonemal or peri-axonemal) and their potential functions. We will categorize the identified MMAF genes following the protein complexes, functions or biological processes they may be associated with, based on the current knowledge in the field.

Assembly, Functions and Evolution of Archaella, Flagella and Cilia

Cells from all three domains of life on Earth utilize motile macromolecular devices that protrude from the cell surface to generate forces that allow them to swim through fluid media. Research carried out on archaea during the past decade or so has led to the recognition that, despite their common function, the motility devices of the three domains display fundamental differences in their properties and ancestry, reflecting a striking example of convergent evolution. Thus, the flagella of bacteria and the archaella of archaea employ rotary filaments that assemble from distinct subunits that do not share a common ancestor and generate torque using energy derived from distinct fuel sources, namely chemiosmotic ion gradients and FlaI motor-catalyzed ATP hydrolysis, respectively. The cilia of eukaryotes, however, assemble via kinesin-2-driven intraflagellar transport and utilize microtubules and ATP-hydrolyzing dynein motors to beat in a variety of waveforms via a sliding filament mechanism. Here, with reference to current structural and mechanistic information about these organelles, we briefly compare the evolutionary origins, assembly and tactic motility of archaella, flagella and cilia.

The functional anatomy of the human spermatozoon: relating ultrastructure and function

The Internet, magazine articles, and even biomedical journal articles, are full of cartoons of spermatozoa that bear minimal resemblance to real spermatozoa, especially human spermatozoa, and this had led to many misconceptions about what spermatozoa look like and how they are constituted. This review summarizes the historical and current state of knowledge of mammalian sperm ultrastructure, with particular emphasis on and relevance to human spermatozoa, combining information obtained from a variety of electron microscopic (EM) techniques. Available information on the composition and configuration of the various ultrastructural components of the spermatozoon has been related to their mechanistic purpose and roles in the primary aspects of sperm function and fertilization: motility, hyperactivation, capacitation, the acrosome reaction and sperm-oocyte fusion.