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.

CCDC181 is required for sperm flagellum biogenesis and male fertility in mice.

The structural integrity of the sperm flagellum is essential for proper sperm function. Flagellar defects can result in male infertility, yet the precise mechanisms underlying this relationship are not fully understood. CCDC181, a coiled-coil domain-containing protein, is known to localize on sperm flagella and at the basal regions of motile cilia. Despite this knowledge, the specific functions of CCDC181 in flagellum biogenesis remain unclear. In this study, Ccdc181 knockout mice were generated. The absence of CCDC181 led to defective sperm head shaping and flagellum formation. Furthermore, the Ccdc181 knockout mice exhibited extremely low sperm counts, grossly aberrant sperm morphologies, markedly diminished sperm motility, and typical multiple morphological abnormalities of the flagella (MMAF). Additionally, an interaction between CCDC181 and the MMAF-related protein LRRC46 was identified, with CCDC181 regulating the localization of LRRC46 within sperm flagella. These findings suggest that CCDC181 plays a crucial role in both manchette formation and sperm flagellum biogenesis.

Microfluidic sperm trap array for single-cell flagellar analysis with unrestricted 2D flagellar movement.

Sperm capture techniques that immobilize sperm to halt their motility are essential for the long-term analysis of individual sperm. These techniques are beneficial in assisted reproductive technologies such as intracytoplasmic sperm injection (ICSI) by allowing selective screening of sperm. However, there is a notable lack of high-throughput and non-destructive sperm capture methods that allow the flagellum to beat freely, which is crucial for accurately reflecting the behavior of unfettered, freely swimming sperm. To bridge this gap, we introduce a novel microfluidic device specifically engineered to capture sperm without restricting flagellar motion. The design utilizes sperm's innate boundary-following behavior in both 3D and 2D environments to direct them into a capture zone. Once captured, the sperm head is restrained while the flagellum remains free to exhibit natural beating patterns. Utilizing this device, we explore the effects of hyperactivating agents, temperature, and their combined influence on the dynamics of bovine sperm flagella. The unrestricted flagellar motion offered by our device yields two prominent advantages: it mirrors the flagellar behavior of free-swimming sperm, ensuring research findings are consistent with natural sperm activity, and it prevents imaging overlap between the flagellum and the capture structures, simplifying the automation of flagellar tracking and analysis. This technological advancement facilitates the collection of waveform parameters along the entire flagellum, addressing inconsistencies that have arisen in previous research due to differing measurement sites, and enabling precise extraction of sperm behavioral properties.

Hybrid motility mechanism of sperm at viscoelastic fluid-solid interface.

To fertilize eggs, sperm must pass through narrow, complex channels filled with viscoelastic fluids in the female reproductive tract. While it is known that the topography of the surfaces plays a role in guiding sperm movement, sperm have been thought of as swimmers, i.e., their motility comes solely from sperm interaction with the surrounding fluid, and therefore, the surfaces have no direct role in the motility mechanism itself. Here, we examined the role of solid surfaces in the movement of sperm in a highly viscoelastic medium. By visualizing the flagellum interaction with surfaces in a microfluidic device, we found that the flagellum stays close to the surface while the kinetic friction between the flagellum and the surface is in the direction of sperm movement, providing thrust. Additionally, the flow field generated by sperm suggests slippage between the viscoelastic fluid and the solid surface, deviating from the no-slip boundary typically used in standard fluid dynamics models. These observations point to hybrid motility mechanisms in sperm involving direct flagellum-surface interaction in addition to flagellum pushing the fluid. This finding signifies an evolutionary strategy of mammalian sperm crucial for their efficient migration through narrow, mucus-filled passages of the female reproductive tract.

A homozygous ARMC3 splicing variant causes asthenozoospermia and flagellar disorganization in a consanguineous family.

Male infertility due to asthenozoospermia is quite frequent, but its etiology is poorly understood. We recruited two infertile brothers, born to first-cousin parents from Pakistan, displaying idiopathic asthenozoospermia with mild stuttering disorder but no ciliary-related symptoms. Whole-exome sequencing identified a splicing variant (c.916+1G>A) in ARMC3, recessively co-segregating with asthenozoospermia in the family. The ARMC3 protein is evolutionarily highly conserved and is mostly expressed in the brain and testicular tissue of human. The ARMC3 splicing mutation leads to the exclusion of exon 8, resulting in a predicted truncated protein (p.Glu245_Asp305delfs*16). Quantitative real-time PCR revealed a significant decrease at mRNA level for ARMC3 and Western blot analysis did not detect ARMC3 protein in the patient's sperm. Individuals homozygous for the ARMC3 splicing variant displayed reduced sperm motility with frequent morphological abnormalities of sperm flagella. Transmission electron microscopy of the affected individual IV: 2 revealed vacuolation in sperm mitochondria at the midpiece and disrupted flagellar ultrastructure in the principal and end piece. Altogether, our results indicate that this novel homozygous ARMC3 splicing mutation destabilizes sperm flagella and leads to asthenozoospermia in our patients, providing a novel marker for genetic counseling and diagnosis of male infertility.

Association of novel DNAH11 variants with asthenoteratozoospermia lead to male infertility.

BACKGROUND: Bi-allelic variants in DNAH11 have been identified as causative factors in Primary Ciliary Dyskinesia, leading to abnormal respiratory cilia. Nonetheless, the specific impact of these variants on human sperm flagellar and their involvement in male infertility remain largely unknown. METHODS: A collaborative effort involving two Chinese reproductive centers conducted a study with 975 unrelated infertile men. Whole-exome sequencing was employed for variant screening, and Sanger sequencing confirmed the identified variants. Morphological and ultrastructural analyses of sperm were conducted using Scanning Electron Microscopy and Transmission Electron Microscopy. Western Blot Analysis and Immunofluorescence Analysis were utilized to assess protein levels and localization. ICSI was performed to evaluate its efficacy in achieving favorable pregnancy outcomes for individuals with DNAH11 variants. RESULTS: In this study, we identified seven novel variants in the DNAH11 gene in four asthenoteratozoospermia subjects. These variants led the absence of DNAH11 proteins and ultrastructure defects in sperm flagella, particularly affecting the outer dynein arms (ODAs) and adjacent structures. The levels of ODA protein DNAI2 and axoneme related proteins were down regulated, instead of inner dynein arms (IDA) proteins DNAH1 and DNAH6. Two out of four individuals with DNAH11 variants achieved clinical pregnancies through ICSI. The findings confirm the association between male infertility and bi-allelic deleterious variants in DNAH11, resulting in the aberrant assembly of sperm flagella and contributing to asthenoteratozoospermia. Importantly, ICSI emerges as an effective intervention for overcoming reproductive challenges caused by DNAH11 gene variants.

The proximal centriole-like structure maintains nucleus-centriole architecture in sperm.

Proper connection between the sperm head and tail is critical for sperm motility and fertilization. Head-tail linkage is mediated by the head-tail coupling apparatus (HTCA), which secures the axoneme (tail) to the nucleus (head). However, the molecular architecture of the HTCA is poorly understood. Here, we use Drosophila to investigate formation and remodeling of the HTCA throughout spermiogenesis by visualizing key components of this complex. Using structured illumination microscopy, we demonstrate that key HTCA proteins Spag4 and Yuri form a 'centriole cap' that surrounds the centriole (or basal body) as it invaginates into the surface of the nucleus. As development progresses, the centriole is laterally displaced to the side of the nucleus while the HTCA expands under the nucleus, forming what we term the 'nuclear shelf'. We next show that the proximal centriole-like (PCL) structure is positioned under the nuclear shelf, functioning as a crucial stabilizer of centriole-nucleus attachment. Together, our data indicate that the HTCA is a complex, multi-point attachment site that simultaneously engages the PCL, the centriole and the nucleus to ensure proper head-tail connection during late-stage spermiogenesis.

MYCBPAP is a central apparatus protein required for centrosome-nuclear envelope docking and sperm tail biogenesis in mice.

The structure of the sperm flagellar axoneme is highly conserved across species and serves the essential function of generating motility to facilitate the meeting of spermatozoa with the egg. During spermiogenesis, the axoneme elongates from the centrosome, and subsequently the centrosome docks onto the nuclear envelope to continue tail biogenesis. Mycbpap is expressed predominantly in mouse and human testes and conserved in Chlamydomonas as FAP147. A previous cryo-electron microscopy analysis has revealed the localization of FAP147 to the central apparatus of the axoneme. Here, we generated Mycbpap-knockout mice and demonstrated the essential role of Mycbpap in male fertility. Deletion of Mycbpap led to disrupted centrosome-nuclear envelope docking and abnormal flagellar biogenesis. Furthermore, we generated transgenic mice with tagged MYCBPAP, which restored the fertility of Mycbpap-knockout males. Interactome analyses of MYCBPAP using Mycbpap transgenic mice unveiled binding partners of MYCBPAP including central apparatus proteins, such as CFAP65 and CFAP70, which constitute the C2a projection, and centrosome-associated proteins, such as CCP110. These findings provide insights into a MYCBPAP-dependent regulation of the centrosome-nuclear envelope docking and sperm tail biogenesis.

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.

Novel mutations in LRRC23 cause asthenozoospermia in a nonconsanguineous family.

ABSTRACT: The cause of asthenozoospermia (AZS) is not well understood because of its complexity and heterogeneity. Although some gene mutations have been identified as contributing factors, they are only responsible for a small number of cases. Radial spokes (RSs) are critical for adenosine triphosphate-driven flagellar beating and axoneme stability, which is essential for flagellum motility. In this study, we found novel compound heterozygous mutations in leucine-rich repeat-containing protein 23 ( LRRC23 ; c.1018C>T: p.Q340X and c.881_897 Del: p.R295Gfs*32) in a proband from a nonconsanguineous family with AZS and male infertility. Diff-Quik staining and scanning electron microscopy revealed no abnormal sperm morphology. Western blotting and immunofluorescence staining showed that these mutations suppressed LRRC23 expression in sperm flagella. Additionally, transmission electron microscopy showed the absence of RS3 in sperm flagella, which disrupts stability of the radial spoke complex and impairs motility. Following in vitro fertilization and embryo transfer, the proband's spouse achieved successful pregnancy and delivered a healthy baby. In conclusion, our study indicates that two novel mutations in LRRC23 are associated with AZS, but successful fertility outcomes can be achieved by in vitro fertilization-embryo transfer techniques.

Homozygous ACTL9 mutations cause irregular mitochondrial sheath arrangement and abnormal flagellum assembly in spermatozoa and male infertility.

PURPOSE: To identify novel variants in ACTL9 and new phenotypes responsible for male infertility. METHODS: Genomic DNA was extracted from peripheral blood samples for whole-exome sequencing (WES). Computer-assisted sperm analysis (CASA) was used to test the motility of spermatozoa. The ultrastructure of flagella and the mitochondrial sheath were assessed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Immunostaining was used to validate the localization and expression of ACTL9 and ACTL7A. An Actl9-mutated mouse model was used to validate the phenotypes by CASA and TEM. RESULTS: We identified novel homozygous variants in ACTL9 in two independent Chinese families. Spermatozoa with ACTL9 mutations showed decreased CASA parameters and a higher proportion of spermatozoa with abnormal morphology, exhibiting coiled flagella and a thickened midpiece. The spermatozoa were characterized by chaotic or irregular '9+2' structures and irregular mitochondrial sheath arrangements in the flagellum. Actl9 knock-in mice also showed abnormal CASA parameters and irregular '9+2' structures in flagella. CONCLUSIONS: Our study expands the mutation spectrum and phenotypic spectrum of ACTL9.

A novel homozygous missense TTC12 variant identified in an infertile Pakistani man with severe oligoasthenoteratozoospermia and primary ciliary dyskinesia.

TTC12 is a cytoplasmic and centromere-localized protein that plays a role in the proper assembly of dynein arm complexes in motile cilia in both respiratory cells and sperm flagella. This finding underscores its significance in cellular motility and function. However, the wide role of TTC12 in human spermatogenesis-associated primary ciliary dyskinesia (PCD) still needs to be elucidated. Whole-exome sequencing (WES) and Sanger sequencing were performed to identify potentially pathogenic variants causing PCD and multiple morphological abnormalities of sperm flagella (MMAF) in an infertile Pakistani man. Diagnostic imaging techniques were used for PCD screening in the patient. Real-time polymerase chain reaction (RT‒PCR) was performed to detect the effect of mutations on the mRNA abundance of the affected genes. Papanicolaou staining and scanning electron microscopy (SEM) were carried out to examine sperm morphology. Transmission electron microscopy (TEM) was performed to examine the ultrastructure of the sperm flagella, and the results were confirmed by immunofluorescence staining. Using WES and Sanger sequencing, a novel homozygous missense variant (c.C1069T; p.Arg357Trp) in TTC12 was identified in a patient from a consanguineous family. A computed tomography scan of the paranasal sinuses confirmed the symptoms of the PCD. RT-PCR showed a decrease in TTC12 mRNA in the patient's sperm sample. Papanicolaou staining, SEM, and TEM analysis revealed a significant change in shape and a disorganized axonemal structure in the sperm flagella of the patient. Immunostaining assays revealed that TTC12 is distributed throughout the flagella and is predominantly concentrated in the midpiece in normal spermatozoa. In contrast, spermatozoa from patient deficient in TTC12 showed minimal staining intensity for TTC12 or DNAH17 (outer dynein arms components). This could lead to MMAF and result in male infertility. This novel TTC12 variant not only illuminates the underlying genetic causes of male infertility but also paves the way for potential treatments targeting these genetic factors. This study represents a significant advancement in understanding the genetic basis of PCD-related infertility.

Structure and Composition of Spermatozoa Fibrous Sheath in Diverse Groups of Metazoa.

The proper functioning and assembly of the sperm flagella structures contribute significantly to spermatozoa motility and overall male fertility. However, the fine mechanisms of assembly steps are poorly studied due to the high diversity of cell types, low solubility of the corresponding protein structures, and high tissue and cell specificity. One of the open questions for investigation is the attachment of longitudinal columns to the doublets 3 and 8 of axonemal microtubules through the outer dense fibers. A number of mutations affecting the assembly of flagella in model organisms are known. Additionally, evolutionary genomics data and comparative analysis of flagella morphology are available for a set of non-model species. This review is devoted to the analysis of diverse ultrastructures of sperm flagellum of Metazoa combined with an overview of the evolutionary distribution and function of the mammalian fibrous sheath proteins.

Egg multivesicular bodies elicit an LC3-associated phagocytosis-like pathway to degrade paternal mitochondria after fertilization.

Mitochondria are maternally inherited, but the mechanisms underlying paternal mitochondrial elimination after fertilization are far less clear. Using Drosophila, we show that special egg-derived multivesicular body vesicles promote paternal mitochondrial elimination by activating an LC3-associated phagocytosis-like pathway, a cellular defense pathway commonly employed against invading microbes. Upon fertilization, these egg-derived vesicles form extended vesicular sheaths around the sperm flagellum, promoting degradation of the sperm mitochondrial derivative and plasma membrane. LC3-associated phagocytosis cascade of events, including recruitment of a Rubicon-based class III PI(3)K complex to the flagellum vesicular sheaths, its activation, and consequent recruitment of Atg8/LC3, are all required for paternal mitochondrial elimination. Finally, lysosomes fuse with strings of large vesicles derived from the flagellum vesicular sheaths and contain degrading fragments of the paternal mitochondrial derivative. Given reports showing that in some mammals, the paternal mitochondria are also decorated with Atg8/LC3 and surrounded by multivesicular bodies upon fertilization, our findings suggest that a similar pathway also mediates paternal mitochondrial elimination in other flagellated sperm-producing organisms.

AXDND1 is required to balance spermatogonial commitment and for sperm tail formation in mice and humans.

Dynein complexes are large, multi-unit assemblies involved in many biological processes via their critical roles in protein transport and axoneme motility. Using next-generation sequencing of infertile men presenting with low or no sperm in their ejaculates, we identified damaging variants in the dynein-related gene AXDND1. We thus hypothesised that AXDND1 is a critical regulator of male fertility. To test this hypothesis, we produced a knockout mouse model. Axdnd1-/- males were sterile at all ages but presented with an evolving testis phenotype wherein they could undergo one round of histologically replete spermatogenesis followed by a rapid depletion of the seminiferous epithelium. Marker experiments identified a role for AXDND1 in maintaining the balance between differentiation-committed and self-renewing spermatogonial populations, resulting in disproportionate production of differentiating cells in the absence of AXDND1 and increased sperm production during initial spermatogenic waves. Moreover, long-term spermatogonial maintenance in the Axdnd1 knockout was compromised, ultimately leading to catastrophic germ cell loss, destruction of blood-testis barrier integrity and immune cell infiltration. In addition, sperm produced during the first wave of spermatogenesis were immotile due to abnormal axoneme structure, including the presence of ectopic vesicles and abnormalities in outer dense fibres and microtubule doublet structures. Sperm output was additionally compromised by a severe spermiation defect and abnormal sperm individualisation. Collectively these data identify AXDND1 as an atypical dynein complex-related protein with a role in protein/vesicle transport of relevance to spermatogonial function and sperm tail formation in mice and humans. This study underscores the importance of studying the consequences of gene loss-of-function on both the establishment and maintenance of male fertility.

Identification of a Homozygous Mutation of CCDC40 in a Chinese Infertile Man with MMAF and PCD-like Phenotypes.

Aims: Asthenozoospermia is the most common factor of male infertility, mainly caused by multiple morphological abnormalities of the sperm flagella (MMAF) and primary ciliary dyskinesia (PCD). Previous studies have shown that genetic factors may contribute to MMAF and PCD. The study aimed to identify novel potentially pathogenic gene mutations in a Chinese infertile man with MMAF and PCD-like phenotypes. Methods: A Chinese infertile man with MMAF and PCD was enrolled in this study. Whole exome sequencing and Sanger sequencing were performed to identify potential causative genes and mutations. Results: A novel homozygous missense mutation (c.1450G>A; p.E484K) of CCDC40 was finally identified and Sanger sequencing confirmed that the patient carried the homozygous mutation, which was inherited from his parents. We reported the first homozygous missense CCDC40 mutation in infertile men with MMAF but had other milder PCD symptoms. Conclusion: Our findings not only broaden the disease-causing mutation spectrum of CCDC40 but also provide new insight into the correlation between CCDC40 mutations and MMAF.

SUN5 interacts with nuclear membrane LaminB1 and cytoskeletal GTPase Septin12 mediating the sperm head-and-tail junction.

Acephalic spermatozoa syndrome (ASS) is a severe teratospermia with decaudated, decapitated, and malformed sperm, resulting in male infertility. Nuclear envelope protein SUN5 localizes to the junction between the sperm head and tail. Mutations in the SUN5 gene have been identified most frequently (33-47%) in ASS cases, and its molecular mechanism of action is yet to be explored. In the present study, we generated Sun5 knockout mice, which presented the phenotype of ASS. Nuclear membrane protein LaminB1 and cytoskeletal GTPases Septin12 and Septin2 were identified as potential partners for interacting with SUN5 by immunoprecipitation-mass spectrometry in mouse testis. Further studies demonstrated that SUN5 connected the nucleus by interacting with LaminB1 and connected the proximal centriole by interacting with Septin12. The binding between SUN5 and Septin12 promoted their aggregation together in the sperm neck. The disruption of the LaminB1/SUN5/Septin12 complex by Sun5 deficiency caused separation of the Septin12-proximal centriole from the nucleus, leading to the breakage of the head-to-tail junction. Collectively, these data provide new insights into the pathogenesis of ASS caused by SUN5 deficiency.

Decreased embryo developmental potential and lower cumulative pregnancy rate in men with multiple morphological abnormalities of the sperm flagella.

Objective: Multiple morphological abnormalities of the sperm flagella (MMAF) is characterized by abnormal flagellar phenotypes, which is a particular kind of asthenoteratozoospermia. Previous studies have reported a comparable intracytoplasmic sperm injection (ICSI) outcome in terms of fertilization rate and clinical pregnancy rate in patients with MMAF compared with those with no MMAF; however, others have conflicting opinions. Assisted reproductive technology (ART) outcomes in individuals with MMAF are still controversial and open to debate. Methods: A total of 38 patients with MMAF treated at an academic reproductive center between January 2014 and July 2022 were evaluated in the current retrospective cohort study and followed up until January 2023. Propensity score matching was used to adjust for the baseline clinical characteristics of the patients and to create a comparable control group. The genetic pathogenesis of MMAF was confirmed by whole exome sequencing. The main outcomes were the embryo developmental potential, the cumulative pregnancy rate (CLPR), and the cumulative live birth rate (CLBR). Results: Pathogenic variants in known genes of DNAH1, DNAH11, CFAP43, FSIP2, and SPEF2 were identified in patients with MMAF. Laboratory outcomes, including the fertilization rate, 2PN cleavage rate, blastocyst formation rate, and available blastocyst rate, followed a trend of decline in the MMAF group (p < 0.05). Moreover, according to the embryo transfer times and complete cycles, the CLPR in the cohort of MMAF was lower compared with the oligoasthenospermia pool (p = 0.033 and p = 0.020, respectively), while no statistical differences were observed in the neonatal outcomes. Conclusion: The current study presented decreased embryo developmental potential and compromised clinical outcomes in the MMAF cohort. These findings may provide clinicians with evidence to support genetic counseling and clinical guidance in specific patients with MMAF.

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.