Novel Mutations in CFAP44 and CFAP43 Cause Multiple Morphological Abnormalities of the Sperm Flagella (MMAF)

Conserved genes regulating human sex differentiation, gametogenesis and fertilization

The study of the functional genome in mice and humans has been instrumental for describing the conserved molecular mechanisms regulating human reproductive biology, and for defining the etiologies of monogenic fertility disorders. Infertility is a reproductive disorder that includes various conditions affecting a couple's ability to achieve a healthy pregnancy. Recent advances in next-generation sequencing and CRISPR/Cas-mediated genome editing technologies have facilitated the identification and characterization of genes and mechanisms that, if affected, lead to infertility. We report established genes that regulate conserved functions in fundamental reproductive processes (e.g., sex determination, gametogenesis, and fertilization). We only cover genes the deletion of which yields comparable fertility phenotypes in both rodents and humans. In the case of newly-discovered genes, we report the studies demonstrating shared cellular and fertility phenotypes resulting from loss-of-function mutations in both species. Finally, we introduce new model systems for the study of human reproductive biology and highlight the importance of studying human consanguineous populations to discover novel monogenic causes of infertility. The rapid and continuous screening and identification of putative genetic defects coupled with an efficient functional characterization in animal models can reveal novel mechanisms of gene function in human reproductive tissues.

Molecular genetic mechanisms of teratozoospermia

In recent years, the incidence of teratospermia has been increasing, and it has become a very important factor leading to male infertility. The research on the molecular mechanism of teratospermia is also progressing rapidly. This article briefly summarizes the clinical incidence of teratozoospermia, and makes a retrospective summary of related studies reported in recent years. Specifically discussing the relationship between gene status and spermatozoa, the review aims to provide the basis for the genetic diagnosis and gene therapy of teratozoospermia.

Identification of sex-specific splicing via comparative transcriptome analysis of gonads from sea cucumber Apostichopus japonicus

Alternative splicing (AS) is an essential post-transcriptional regulation mechanism for sex differentiation and gonadal development, which has rarely been reported in marine invertebrates. Sea cucumber (Apostichopus japonicus) is an economically important marine benthic echinoderm with a potential XX/XY sex determination mechanism, whose molecular mechanism in the gonadal differentiation has not been clearly understood. In this study, we analyzed available RNA-seq datasets of male and female gonads to explore if AS mechanism exerts an essential function in sex differentiation and gonadal development of A. japonicus. In our results, a total of 20,338 AS events from 7219 alternatively spliced genes, and 189 sexually differential alternative splicing (DAS) events from 156 genes were identified in gonadal transcriptome of sea cucumber. Gene Ontology analysis indicated that these DAS genes were significantly enriched in spermatogenesis-related GO terms. Maximal Clique Centrality (MCC) was then applied for protein-protein interaction (PPI) analysis to search for protein interactions and hub DAS gene. Among all DAS genes, we identified 10 DAS genes closely related to spermatogenesis and (or) sperm motility and a hub gene dnah1. Thus, this study revealed that alternative isoforms were generated from certain genes in female and male gonads through alternative splicing, which may provide direct evidence that alternative splicing mechanisms participate in female and male gonads. These results suggested a novel perspective for explaining the molecular mechanisms underlying gonadal differentiation between male and female sea cucumbers.

Compound Heterozygous Mutations in FSIP2 Cause Morphological Abnormalities in Sperm Flagella Leading to Male Infertility

Multiple morphological abnormalities of sperm flagella (MMAF) indicate severe teratozoospermia. The fibrous sheath interacting protein 2 (FSIP2) plays an important role in the normal construction of the flagella. In this study, a novel compound heterozygous mutation site of FSIP2, involving c.272_275delinsAGGTTTTTATA (p.L92Vfster74) and c.16788_16791del (p.E5596fs), was identified using whole-exome sequencing in a 32-year-old male. Electron microscope images revealed thick sperm neck, scattered sperm mitochondria, and short sperm tail. In addition, FSIP2 could not be visualized in sperm cells via immunofluorescence staining. Moreover, we used a protein domain prediction tool to identify a potential FSIP2 functional domain (5901-6774), the corresponding deletion of which was responsible for the MMAF phenotype in the infertile man. Finally, we reviewed the literature on FSIP2 and found that FSIP2 mutations are relatively concentrated, with high-frequency mutation regions in exon 16 and exon 17 accounting for 50% (10/20) and 35% (7/20) of cases, respectively. In conclusion, FISP2 is a common pathogenic gene of MMAF, which may provide a rationale for genetic counseling in the next generation of patients with male infertility.

Reduced expression of CFAP44 and CFAP44-AS1 may affect sperm motility and morphology

Motility and morphology are two important characteristics of a fertile spermatozoon. CFAP44 gene encodes flagellar protein 44 involved in the formation and function of the flagella and cilia. Long non-coding RNAs are regulatory elements involved in several processes, including reproduction. We aimed to study the alterations in the expressions of CFAP44 and CFAP44-AS1 genes in infertile men with asthenozoospermia and terato-asthenozoospermia. In this case-control study, a total of 105 subjects, including 35 TAZ patients, 34 AZ patients and 35 normozoospermic men, were enrolled. After RNA extraction from spermatozoa samples, quantitative real-time PCR was performed to compare the expression of CFAP44 and CFAP44-AS1 between the studied groups. A meaningful reduction in CFAP44 expression and a significant reduction in the expression of CFAP44-AS1 were observed. Moreover, a positive correlation between both genes' expressions and normal sperm morphology was detected in NZ, AZ and TAZ groups. Also, there was a positive relation between CFAP44 gene expression and sperm motility in AZ and TAZ groups. The expression of CFAP44-AS1 was positively correlated with sperm motility and morphology. Present results confirm the role of CFAP44 and CFAP44-AS1 in the motility and morphology of spermatozoon, and deregulation of these genes may contribute to male infertility.

PCD Genes-From Patients to Model Organisms and Back to Humans

Primary ciliary dyskinesia (PCD) is a hereditary genetic disorder caused by the lack of motile cilia or the assembxly of dysfunctional ones. This rare human disease affects 1 out of 10,000-20,000 individuals and is caused by mutations in at least 50 genes. The past twenty years brought significant progress in the identification of PCD-causative genes and in our understanding of the connections between causative mutations and ciliary defects observed in affected individuals. These scientific advances have been achieved, among others, due to the extensive motile cilia-related research conducted using several model organisms, ranging from protists to mammals. These are unicellular organisms such as the green alga Chlamydomonas, the parasitic protist Trypanosoma, and free-living ciliates, Tetrahymena and Paramecium, the invertebrate Schmidtea, and vertebrates such as zebrafish, Xenopus, and mouse. Establishing such evolutionarily distant experimental models with different levels of cell or body complexity was possible because both basic motile cilia ultrastructure and protein composition are highly conserved throughout evolution. Here, we characterize model organisms commonly used to study PCD-related genes, highlight their pros and cons, and summarize experimental data collected using these models.

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.

Mutations in DNAH8 contribute to multiple morphological abnormalities of sperm flagella and male infertility

Asthenoteratospermia is an important cause of male infertility. Here, we report two infertile patients with severe asthenoteratospermia accompanied by new genetic abnormality. Whole-exome sequencing and bioinformatics analysis suggested that compound heterozygous mutations in DNAH8 (MIM:603337) may be responsible for multiple morphological abnormalities of the sperm flagella (MMAF). Immunofluorescence assay showed that DNAH8 protein expression was significantly decreased in the sperm tail of the patients, and electron microscopy exhibited an abnormal flagellum ultrastructure, while clinical pregnancy could be achieved by intracytoplasmic sperm injection. Therefore, the compound heterozygous mutations in the DNAH8 gene may be responsible for MMAF.

Biallelic mutations of CFAP58 are associated with multiple morphological abnormalities of the sperm flagella

Multiple morphological abnormalities of the sperm flagella (MMAF) is a severe type of teratozoospermia. In this study, whole-exome sequencing was conducted on 55 patients with MMAF, and biallelic mutations of CFAP58 were identified in two patients. The variants are rare and pathogenic, and CFAP58 was absent in the CFAP58-mutated sperm. The F037/II:1 couple benefited from intracytoplasmic sperm injection (ICSI). This study further indicated that CFAP58 is a pathogenic gene associated with MMAF and ICSI is an effective treatment.

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

BACKGROUND

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

OBJECTIVE AND RATIONALE

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

SEARCH METHODS

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

OUTCOMES

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

WILDER IMPLICATIONS

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

Biallelic mutations of CFAP74 may cause human primary ciliary dyskinesia and MMAF phenotype

Primary ciliary dyskinesia (PCD) is a rare genetic disorder characterized by recurrent respiratory infections, nasosinusitis, tympanitis, and/or male infertility, all of which can severely impair the patient's quality of life. Multiple morphological abnormalities of the sperm flagella (MMAF) is one type of severe teratozoospermia and results from a variety of flagellar defects. In this study, we conducted whole-exome sequencing to identify and evaluate the genetic lesions in two patients with potential PCD and MMAF. Biallelic mutations in exon 10, c.983G>A; p.(Gly328Asp), and exon 29, c.3532G>A; p.(Asp1178Asn), of the CFAP74 (NM_001304360) gene were identified in patient 1 (P1), and biallelic mutations in exon 7, c.652C>T; p.(Arg218Trp), and exon 35, c. 4331G>C; p.(Ser1444Thr), of the same gene were identified in patient 2 (P2). Bioinformatic analysis suggested that these variants may be disease causing. Immunofluorescence confirmed that CFAP74 was absent in these patients' sperm samples. Intracytoplasmic sperm injection (ICSI) was carried out for P1, and his wife became pregnant after embryo transfer and gave birth to a healthy baby. To the best of our knowledge, this study is the first to identify the importance of CFAP74 in potential PCD and MMAF, contributing to the genetic diagnosis of these disorders and helping to predict pregnancy outcomes relevant in in vitro fertilization.

Fluoride exposure alters the ultra-structure of sperm flagellum via reducing key protein expressions in testis

Excessive fluoride (F) ingestion via drinking water interfered with spermatogenesis and lowered sperm quality of human and animals. However, it is still unclear why the effects of fluoride on sperm quality focus on mostly sperm motility rather than sperm count. The objective of this study is to investigate the potential relationship between alteration in the structure and function of sperm flagellum and fluoride exposure in the environment. 40 male mice were allocated to four groups which were treated with 0, 25, 50, 100 mg/L NaF deionized water, respectively, for 8 weeks continuously. The testicular morphology, ultra-structure of fibrous sheath and axoneme of sperm flagellum, and eleven key function genes Akap3, Akap4, Dnah1, Eno4, Cfap43, Cfap44, Hydin, Spef2, Spag6, Spag16, and Cfap69 were examined by histology, transmission electron microscopy, and real-time PCR methods respectively. The results displayed that fluoride damaged the typical "9 + 2″ microtubule structure including fibrous sheathes and axoneme of sperm flagellum in testes of mice. Furthermore, the mRNA and protein expression levels of AKAP3 and AKAP4 related to fibrous sheathes formation, and CFAP43, CFAP44 and HYDIN in axoneme were down-regulated by fluoride exposure. Taken together, we revealed that fluoride altered the structures of the fibrous sheathes and axonemal in sperm flagellum via down-regulating the mRNA and protein expression levels of AKAP3, AKAP4, CFAP43, CFAP44, and HYDIN, which may be one of the reasons that fluoride lowered sperm quality and male reproductive function.

Mutational effect of human CFAP43 splice-site variant causing multiple morphological abnormalities of the sperm flagella

Multiple morphological abnormalities of the sperm flagella (MMAF) is a rare disease associated with male infertility. In our previous study, we identified a homozygous CFAP43 splice-site variant, c.3661-2delA, in a patient with MMAF. However, the mutational effect of this variant was unknown. Here, using a minigene assay, we demonstrated that the c.3661-2delA variant may cause exon-30 to be skipped, thus generating the p.E1221_K1256del protein. By secondary and three-dimensional structural biology prediction analysis, we found that the mutant protein became 'tighter' in comparison with the wild-type protein, resulting in amino acid rearrangements in CFAP43 protein structure. We elucidated the molecular mechanism of the c.3661-2delA splice-site variant causing MMAF in the current study.

Harnessing the full potential of reproductive genetics and epigenetics for male infertility in the era of "big data"

The complexity of male reproductive impairment has hampered characterization of the underlying genetic causes of male infertility. However, in the last 20 years, more powerful and affordable tools to interrogate the genetic and epigenetic determinants of male infertility have accelerated the number of new discoveries in the characterization of male infertility. With this explosion of new data, integration in a systems-based approach-including complete phenotypic information-to male infertility is imperative. We briefly review the current understanding of genetic and epigenetic causes of male infertility and how findings may be translated into a practical component for the diagnosis and treatment of male infertility.

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.

DNAH17 is associated with asthenozoospermia and multiple morphological abnormalities of sperm flagella

BACKGROUND

Multiple morphological abnormalities of the sperm flagella (MMAF) is one kind of severe asthenozoospermia, which is caused by dysplastic development of sperm flagella. In our study, we sought to investigate the novel gene mutations leading to severe asthenozoospermia and MMAF.

METHODS AND MATERIALS

The patient's spermatozoa were tested by Papanicolaou staining and transmission electron microscopy. Whole exome sequencing was performed on the patient with severe asthenozoospermia and MMAF. Sanger sequencing verified the mutations in the family. The expression of DNAH17 was detected by immunofluorescence and Western blot.

RESULTS

Spermatozoa sample from the patient showed severe asthenozoospermia and MMAF. We detected biallelic mutations (c.C4445T, p.A1482V and c.C6857T, and p.S2286L) in DNAH17 (MIM:610063). The protein expression of DNAH17 was almost undetectable in spermatozoa from the patient with the biallelic mutations.

CONCLUSION

These results demonstrated that DNAH17 may be involved in severe asthenozoospermia and MMAF.

Biallelic mutations in Sperm flagellum 2 cause human multiple morphological abnormalities of the sperm flagella (MMAF) phenotype

Male patients with multiple morphological abnormalities of the sperm flagella (MMAF) are infertile and exhibit absent, short, coiled, bent and/or irregular sperm flagella. Mutations in the SPEF2 gene reduce sperm motility and cause sperm tail defects in animal models and humans. In the present study, we performed a genetic analysis on an MMAF patient and identified novel biallelic mutations in the SPEF2 gene. The biallelic mutations were confirmed by Sanger sequencing and in silico analysis revealed that, these variations were deleterious. The expression of truncated SPEF2 protein was reduced significantly in the patient's spermatozoa. The spermatozoa harbored biallelic mutations and showed severe ultrastructural defects in the axoneme and mitochondrial sheath. Our data suggest that biallelic mutations in SPEF2 can cause severe sperm flagellum defects, thus providing a novel candidate genetic pathogen for the human MMAF phenotype.

Whole exome sequencing of men with multiple morphological abnormalities of the sperm flagella reveals novel homozygous QRICH2 mutations

Multiple morphological anomalies of the sperm flagella (MMAF syndrome) is a severe male infertility phenotype which has so far been formally linked to the presence of biallelic mutations in nine genes mainly coding for axonemal proteins overexpressed in the sperm flagellum. Homozygous mutations in QRICH2, a gene coding for a protein known to be required for stabilizing proteins involved in sperm flagellum biogenesis, have recently been identified in MMAF patients from two Chinese consanguineous families. Here, in order to better assess the contribution of QRICH2 in the etiology of the MMAF phenotype, we analyzed all QRICH2 variants from whole exome sequencing data of a cohort of 167 MMAF-affected subjects originating from North Africa, Iran, and Europe. We identified a total of 14 potentially deleterious variants in 18 unrelated individuals. Two unrelated subjects, representing 1% of the cohort, carried a homozygous loss-of-function variant: c.3501C>G [p.Tyr1167Ter] and c.4614C>G [p.Tyr1538Ter], thus confirming the implication of QRICH2 in the MMAF phenotype and human male infertility. Sixteen MMAF patients (9.6%) carried a heterozygous QRICH2 potentially deleterious variant. This rate was comparable to what was observed in a control group (15.5%) suggesting that the presence of QRICH2 heterozygous variants is not associated with MMAF syndrome.

DNAH2 is a novel candidate gene associated with multiple morphological abnormalities of the sperm flagella

Multiple morphological abnormalities of flagella (MMAF) is one kind of severe teratozoospermia. Gene mutations reported in previous works only revealed the pathogenesis of approximately half of the MMAF cases, and more genetic defects in MMAF need to be explored. In the present study, we performed a genetic analysis on Han Chinese men with MMAF using whole-exome sequencing. After filtering out the cases with known gene mutations, we identified five novel mutation sites in the DNAH2 gene in three cases from three families. These mutations were validated through Sanger sequencing and absent in all control individuals. In silico analysis revealed that these DNAH2 variations are deleterious. The spermatozoa with DNAH2 mutations showed severely disarranged axonemal structures with mitochondrial sheath defection. The DNAH2 protein level was significantly decreased and inner dynein arms were absent in the spermatozoa of patients. ICSI treatment was performed for two MMAF patients with DNAH2 mutations and the associated couples successfully achieved pregnancy, indicating good nuclear quality of the sperm from the DNAH2 mutant patients. Together, these data suggest that the DNAH2 mutation can cause severe sperm flagella defects that damage sperm motility. These results provide a novel genetic pathogeny for the human MMAF phenotype.

New insights into the genetics of spermatogenic failure: a review of the literature

Genetic anomalies are known to affect about 15% of infertile patients with azoospermia or severe oligozoospermia. Despite a throughout diagnostic work-up, in up to the 72% of the male partners of infertile couples, no etiological factor can be found; hence, the cause of infertility remains unclear. Recently, several novel genetic causes of spermatogenic failure (SPGF) have been described. The aim of this review was to collect all the available evidence of SPGF genetics, matching data from in-vitro and animal models with those in human beings to provide a comprehensive and updated overview of the genes capable of affecting spermatogenesis. By reviewing the literature, we provided a list of 60 candidate genes for SPGF. Their investigation by Next Generation Sequencing in large cohorts of patients with apparently idiopathic infertility would provide new interesting data about their racial- and ethnic-related prevalence in infertile patients, likely raising the diagnostic yields. We propose a phenotype-based approach to identify the genes to look for.

Monogenic Forms of Male Infertility

Male infertility is a multifactorial and heterogeneous pathological condition affecting 7% of the general male population. The genetic landscape of male infertility is highly complex as semen and testis histological phenotypes are extremely heterogeneous, and at least 2000 genes are predicted to be involved in spermatogenesis. Genetic factors have been described in each etiological category of male reproductive impairment: (1) hypothalamic-pituitary axis dysfunction; (2) quantitative and qualitative alterations of spermatogenesis; (3) ductal obstruction/dysfunction. In 25% of azoospermic and in 10% of oligozoospermic men, a genetic anomaly can be diagnosed with the current genetic testing. However, up to now, only a relatively low number of monogenic factors have a clear-cut cause-effect relationship with impaired reproductive function. Thanks to the widespread diffusion of Next-Generation Sequencing, a continuously increasing number of monogenic causes of male infertility are being discovered and their validation is currently ongoing. The identification of genetic factors is of outmost clinical importance since there is a risk of transmission of genetic defects through natural or assisted reproductive techniques. The benefit of the genetic diagnosis of infertility has an obvious clinical significance for the patient itself with implications not only for his reproductive health but in many instances also for his general health.

Novel homozygous CFAP69 mutations in humans and mice cause severe asthenoteratospermia with multiple morphological abnormalities of the sperm flagella

BACKGROUND

Male infertility is a major issue of human reproduction health. Asthenoteratospermia can impair sperm motility and cause male infertility. Asthenoteratospermia with multiple morphological abnormalities of the flagella (MMAF) presents abnormal spermatozoa with absent, bent, coiled, short and/or irregular-calibre flagella. Previous studies on MMAF reported that genetic defects in cilia-related genes (eg, AKAP4, DNAH1, CFAP43, CFAP44 and CFAP69) are the major cause of MMAF. However, the known MMAF-associated genes are only responsible for approximately 30% to 50% of human cases. We further investigated the cases with MMAF in search of additional genes mutated in this condition.

METHODS AND RESULTS

We conducted whole exome sequencing in a male individual with MMAF from a consanguineous Han Chinese family. Sanger sequencing was also conducted in additional individuals with MMAF. Intriguingly, a homozygous frameshift mutation (p.Leu357Hisfs*11) was identified in the gene encoding CFAP69 (cilia and flagella-associated protein 69), which is highly expressed in testis. The subsequent Sanger sequencing of the CFAP69 coding regions among 34 additional individuals with MMAF revealed a case with homozygous nonsense mutation (p.Trp216*) of CFAP69. Both of these CFAP69 loss-of-function mutations were not present in the human population genome data archived in the 1000 Genomes Project and ExAC databases, nor in 875 individuals of two Han Chinese control populations. Furthermore, we generated the knockout model in mouse orthologue Cfap69 using the CRISPR-Cas9 technology. Remarkably, male Cfap69-knockout mice manifested with MMAF phenotypes.

CONCLUSION

Our experimental findings elucidate that homozygous loss-of-function mutations in CFAP69 can lead to asthenoteratospermia with MMAF in humans and mice.

Loss of Calmodulin- and Radial-Spoke-Associated Complex Protein CFAP251 Leads to Immotile Spermatozoa Lacking Mitochondria and Infertility in Men

Flagella and motile cilia share a 9 + 2 microtubule-doublet axoneme structure, and asthenozoospermia (reduced spermatozoa motility) is found in 76% of men with primary ciliary dyskinesia (PCD). Nevertheless, causal genetic variants in a conserved axonemal component have been found in cases of isolated asthenozoospermia: 30% of men with multiple morphological anomalies of sperm flagella (MMAF) carry bi-allelic mutations in DNAH1, encoding one of the seven inner-arm dynein heavy chains of the 9 + 2 axoneme. To further understand the basis for isolated asthenozoospermia, we used whole-exome and Sanger sequencing to study two brothers and two independent men with MMAF. In three men, we found bi-allelic loss-of-function mutations in WDR66, encoding cilia- and flagella-associated protein 251 (CFAP251): the two brothers were homozygous for the frameshift chr12: g.122359334delA (p.Asp42Metfs^∗4), and the third individual was compound heterozygous for chr12: g.122359542G>T (p.Glu111^∗) and chr12: g.122395032_122395033delCT (p.Leu530Valfs^∗4). We show that CFAP251 is normally located along the flagellum but is absent in men carrying WDR66 mutations and reveal a spermatozoa-specific isoform probably generated during spermatozoon maturation. CFAP251 is a component of the calmodulin- and radial-spoke- associated complex, located adjacent to DNAH1, on the inner surface of the peripheral microtubule doublets of the axoneme. In Tetrahymena, the CFAP251 ortholog is necessary for efficient coordinated ciliary beating. Using immunofluorescent and transmission electron microscopy, we provide evidence that loss of CFAP251 affects the formation of the mitochondrial sheath. We propose that CFAP251 plays a structural role during biogenesis of the spermatozoon flagellum in vertebrates.

A Homozygous Ancestral SVA-Insertion-Mediated Deletion in WDR66 Induces Multiple Morphological Abnormalities of the Sperm Flagellum and Male Infertility

Multiple morphological abnormalities of the sperm flagellum (MMAF) is a severe form of male infertility defined by the presence of a mosaic of anomalies, including short, bent, curled, thick, or absent flagella, resulting from a severe disorganization of the axoneme and of the peri-axonemal structures. Mutations in DNAH1, CFAP43, and CFAP44, three genes encoding axoneme-related proteins, have been described to account for approximately 30% of the MMAF cases reported so far. Here, we searched for pathological copy-number variants in whole-exome sequencing data from a cohort of 78 MMAF-affected subjects to identify additional genes associated with MMAF. In 7 of 78 affected individuals, we identified a homozygous deletion that removes the two penultimate exons of WDR66 (also named CFAP251), a gene coding for an axonemal protein preferentially localized in the testis and described to localize to the calmodulin- and spoke-associated complex at the base of radial spoke 3. Sequence analysis of the breakpoint region revealed in all deleted subjects the presence of a single chimeric SVA (SINE-VNTR-Alu) at the breakpoint site, suggesting that the initial deletion event was potentially mediated by an SVA insertion-recombination mechanism. Study of Trypanosoma WDR66's ortholog (TbWDR66) highlighted high sequence and structural analogy with the human protein and confirmed axonemal localization of the protein. Reproduction of the human deletion in TbWDR66 impaired flagellar movement, thus confirming WDR66 as a gene associated with the MMAF phenotype and highlighting the importance of the WDR66 C-terminal region.