Mutations in ARL2BP, a protein required for ciliary microtubule structure, cause syndromic male infertility in humans and mice

Coding and non-coding variants in the ciliopathy gene CFAP410 cause early-onset non-syndromic retinal degeneration

Inherited retinal degenerations are blinding genetic disorders characterized by high genetic and phenotypic heterogeneity. In this retrospective study, we describe sixteen families with early-onset non-syndromic retinal degenerations in which affected probands carried rare bi-allelic variants in CFAP410, a ciliary gene previously associated with recessive Jeune syndrome. We detected twelve variants, eight of which were novel, including c.373+91A>G, which led to aberrant splicing. To our knowledge this is the first likely pathogenic deep-intronic variant identified in this gene. Analysis of all reported and novel CFAP410 variants revealed no clear correlation between the severity of the CFAP410-associated phenotypes and the identified causal variants. This is supported by the fact that the frequently encountered missense variant p.(Arg73Pro), often found in syndromic cases, was also associated with non-syndromic retinal degeneration. This study expands the current knowledge of CFAP410-associated ciliopathy by enriching its mutational landscape and supports its association with non-syndromic retinal degeneration.

ARL3 GTPases facilitate ODA16 unloading from IFT in motile cilia

Eukaryotic cilia and flagella are essential for cell motility and sensory functions. Their biogenesis and maintenance rely on the intraflagellar transport (IFT). Several cargo adapters have been identified to aid IFT cargo transport, but how ciliary cargos are discharged from the IFT remains largely unknown. During our explorations of small GTPases ARL13 and ARL3 in Trypanosoma brucei, we found that ODA16, a known IFT cargo adapter present exclusively in motile cilia, is a specific effector of ARL3. In the cilia, active ARL3 GTPases bind to ODA16 and dissociate ODA16 from the IFT complex. Depletion of ARL3 GTPases stabilizes ODA16 interaction with the IFT, leading to ODA16 accumulation in cilia and defects in axonemal assembly. The interactions between human ODA16 homolog HsDAW1 and ARL GTPases are conserved, and these interactions are altered in HsDAW1 disease variants. These findings revealed a conserved function of ARL GTPases in IFT transport of motile ciliary components, and a mechanism of cargo unloading from the IFT.

Genetic profile of syndromic retinitis pigmentosa in Portugal

PURPOSE

Retinitis pigmentosa (RP) comprises a genetically and clinically heterogeneous group of inherited retinal degenerations, where 20-30% of patients exhibit extra-ocular manifestations (syndromic RP). Understanding the genetic profile of RP has important implications for disease prognosis and genetic counseling. This study aimed to characterize the genetic profile of syndromic RP in Portugal.

METHODS

Multicenter, retrospective cohort study. Six Portuguese healthcare providers identified patients with a clinical diagnosis of syndromic RP and available genetic testing results. All patients had been previously subjected to a detailed ophthalmologic examination and clinically oriented genetic testing. Genetic variants were classified according to the American College of Medical Genetics and Genomics; only likely pathogenic or pathogenic variants were considered relevant for disease etiology.

RESULTS

One hundred and twenty-two patients (53.3% males) from 100 families were included. Usher syndrome was the most frequent diagnosis (62.0%), followed by Bardet-Biedl (19.0%) and Senior-Løken syndromes (7.0%). Deleterious variants were identified in 86/100 families for a diagnostic yield of 86.0% (87.1% for Usher and 94.7% for Bardet-Biedl). A total of 81 genetic variants were identified in 25 different genes, 22 of which are novel. USH2A and MYO7A were responsible for most type II and type I Usher syndrome cases, respectively. BBS1 variants were the cause of Bardet-Biedl syndrome in 52.6% of families. Best-corrected visual acuity (BCVA) records were available at baseline and last visit for 99 patients (198 eyes), with a median follow-up of 62.0 months. The mean BCVA was 56.5 ETDRS letters at baseline (Snellen equivalent ~ 20/80), declining to 44.9 ETDRS letters (Snellen equivalent ~ 20/125) at the last available follow-up (p < 0.001).

CONCLUSION

This is the first multicenter study depicting the genetic profile of syndromic RP in Portugal, thus contributing toward a better understanding of this heterogeneous disease group. Usher and Bardet-Biedl syndromes were found to be the most common types of syndromic RP in this large Portuguese cohort. A high diagnostic yield was obtained, highlighting current genetic testing capabilities in providing a molecular diagnosis to most affected individuals. This has major implications in determining disease-related prognosis and providing targeted genetic counseling for syndromic RP patients in Portugal.

Genetic Causes of Qualitative Sperm Defects: A Narrative Review of Clinical Evidence

Several genes are implicated in spermatogenesis and fertility regulation, and these genes are presently being analysed in clinical practice due to their involvement in male factor infertility (MFI). However, there are still few genetic analyses that are currently recommended for use in clinical practice. In this manuscript, we reviewed the genetic causes of qualitative sperm defects. We distinguished between alterations causing reduced sperm motility (asthenozoospermia) and alterations causing changes in the typical morphology of sperm (teratozoospermia). In detail, the genetic causes of reduced sperm motility may be found in the alteration of genes associated with sperm mitochondrial DNA, mitochondrial proteins, ion transport and channels, and flagellar proteins. On the other hand, the genetic causes of changes in typical sperm morphology are related to conditions with a strong genetic basis, such as macrozoospermia, globozoospermia, and acephalic spermatozoa syndrome. We tried to distinguish alterations approved for routine clinical application from those still unsupported by adequate clinical studies. The most important aspect of the study was related to the correct identification of subjects to be tested and the correct application of genetic tests based on clear clinical data. The correct application of available genetic tests in a scenario where reduced sperm motility and changes in sperm morphology have been observed enables the delivery of a defined diagnosis and plays an important role in clinical decision-making. Finally, clarifying the genetic causes of MFI might, in future, contribute to reducing the proportion of so-called idiopathic MFI, which might indeed be defined as a subtype of MFI whose cause has not yet been revealed.

A novel homozygous splice site variant in ARL2BP causes a syndromic autosomal recessive rod-cone dystrophy with situs inversus, asthenozoospermia, unilateral renal agenesis and microcysts

BACKGROUND

This report presents a clinical case of syndromic rod-cone dystrophy due to a splice site variant in the ARL2BP gene causing situs inversus, asthenozoospermia, unilateral renal agenesis and microcysts. The presence of renal agenesis and cryptorchidism expands the clinical manifestations due to ARL2BP variants. The detailed, long-term follow-up contributes valuable insights into disease progression, aiding clinical diagnosis and patient management.

CASE PRESENTATION

The male patient complained of photophobia as the first symptom when he was 20 years old followed by nyctalopia, loss of central visual acuity and peripheral visual field ten years later. Genetic analysis identified a likely pathogenic homozygous variant (c.294-1G > C) involving the splicing acceptor site of intron 4. Reported symptoms together with full-field stimulus threshold testing, electroretinogram and advanced multimodal imaging allowed us to recognize the typical characteristics of a mixed retinal dystrophy. Despite the end-stage retinal disease, this patient still retained a useful residual vision at 63 years and had a slow disease progression during the last 5 years of evaluation.

DISCUSSION AND CONCLUSIONS

Our findings underscore the variable clinical presentation of ARL2BP variants, emphasizing the importance of a nuanced approach in diagnosing and managing patients. The presence of renal cysts warrants consideration of a differential diagnosis, particularly with Senior-Loken (SLS), Bardet-Biedl (BBS) and Joubert syndromes (JS) but also with Short Rib Thoracic Dysplasia 9, highlighting the need for careful phenotypic evaluation in these cases.

Coding and non-coding variants in the ciliopathy gene CFAP410 cause early-onset non-syndromic retinal degeneration

Inherited retinal degenerations are blinding genetic disorders characterized by high genetic and phenotypic heterogeneity. The implementation of next-generation sequencing in routine diagnostics, together with advanced clinical phenotyping including multimodal retinal imaging, have contributed to the increase of reports describing novel genotype-phenotype associations and phenotypic expansions. In this study, we describe sixteen families with early-onset non-syndromic retinal degenerations in which affected probands carried rare bi-allelic variants in CFAP410, a ciliary gene previously associated with syndromic recessive Jeune syndrome. The most common retinal phenotypes were cone-rod and rod-cone dystrophies, but the clinical presentations were unified by their early onset as well as the severe impact on central visual function. Twelve variants were detected (three pathogenic, seven likely pathogenic, two of uncertain significance), eight of which were novel. One deep intronic change, c.373+91A>G, led to the creation of a cryptic splice acceptor site in intron four, followed by the inclusion of a 200- base pair pseudoexon and subsequent premature stop codon formation. To our knowledge this is the first likely pathogenic deep-intronic variant identified in this gene. Meta-analysis of all published and novel CFAP410 variants revealed no clear correlation between the severity of the CFAP410-associated phenotypes and the identified causal variants. This is supported by the fact that the frequently encountered missense variant p.(Arg73Pro), often found in syndromic cases, was also associated with non-syndromic retinal degeneration. This study expands the current knowledge of CFAP410-associated ciliopathy by enriching its mutational landscape and supports its association with non-syndromic retinal degeneration.

Novel homozygous variant in ARL2BP associated with retinitis pigmentosa, situs inversus, and male infertility in a Chinese patient

ARL2BP is a ciliary gene associated with multiple ciliopathy phenotypes. On comprehensive clinical examinations using molecular methods, we identified a Chinese patient from a consanguineous family carrying a novel homozygous variant c.22_23delAG (p.S8Lfs*10) in ARL2BP, presenting with retinitis pigmentosa (RP), situs inversus totalis, and oligozoospermia. Situs inversus and male infertility have never been reported in the same patient with ARL2BP variants; therefore, this a novel ARL2BP-associated phenotypic triad of RP, situs inversus, and male infertility. Moreover, this patient likely had olfactory dysfunction susceptibility and presented with anosmia. We found reduced patient-derived fibroblast proliferation and ciliary length. Our findings expand the genotypic spectrum and reveal abnormal cell proliferation and ciliogenesis in ARL2BP-associated patients.

The first genetic landscape of inherited retinal dystrophies in Portuguese patients identifies recurrent homozygous mutations as a frequent cause of pathogenesis

Inherited retinal diseases (IRDs) are a group of ocular conditions characterized by an elevated genetic and clinical heterogeneity. They are transmitted almost invariantly as monogenic traits. However, with more than 280 disease genes identified so far, association of clinical phenotypes with genotypes can be very challenging, and molecular diagnosis is essential for genetic counseling and correct management of the disease. In addition, the prevalence and the assortment of IRD mutations are often population-specific. In this work, we examined 230 families from Portugal, with individuals suffering from a variety of IRD diagnostic classes (270 subjects in total). Overall, we identified 157 unique mutations (34 previously unreported) in 57 distinct genes, with a diagnostic rate of 76%. The IRD mutational landscape was, to some extent, different from those reported in other European populations, including Spanish cohorts. For instance, the EYS gene appeared to be the most frequently mutated, with a prevalence of 10% among all IRD cases. This was, in part, due to the presence of a recurrent and seemingly founder mutation involving the deletion of exons 13 and 14 of this gene. Moreover, our analysis highlighted that as many as 51% of our cases had mutations in a homozygous state. To our knowledge, this is the first study assessing a cross-sectional genotype-phenotype landscape of IRDs in Portugal. Our data reveal a rather unique distribution of mutations, possibly shaped by a small number of rare ancestral events that have now become prevalent alleles in patients.

Arf-like Protein 2 (ARL2) Controls Microtubule Neogenesis during Early Postnatal Photoreceptor Development

Arf-like protein 2 (ARL2) is a ubiquitously expressed small GTPase with multiple functions. In a cell culture, ARL2 participates with tubulin cofactor D (TBCD) in the neogenesis of tubulin αβ-heterodimers, the building blocks of microtubules. To evaluate this function in the retina, we conditionally deleted ARL2 in mouse retina at two distinct stages, either during the embryonic development (retArl2-/-) or after ciliogenesis specifically in rods (rodArl2-/-). retArl2-/- retina sections displayed distorted nuclear layers and a disrupted microtubule cytoskeleton (MTC) as early as postnatal day 6 (P6). Rod and cone outer segments (OS) did not form. By contrast, the rod ARL2 knockouts were stable at postnatal day 35 and revealed normal ERG responses. Cytoplasmic dynein is reduced in retArl2-/- inner segments (IS), suggesting that dynein may be unstable in the absence of a normal MTC. We investigated the microtubular stability in the absence of either ARL2 (retARL2-/-) or DYNC1H1 (retDync1h1-/-), the dynein heavy chain, and found that both the retArl2-/- and retDync1h1-/- retinas exhibited reduced microtubules and nuclear layer distortion. The results suggest that ARL2 and dynein depend on each other to generate a functional MTC during the early photoreceptor development.

Cryopreservation process alters the expression of genes involved in pathways associated with the fertility of bull spermatozoa

In bovines, cryopreserved semen is used for artificial insemination; however, the fertility of cryopreserved semen is far lower than that of fresh semen. Although cryopreservation alters sperm phenotypic characteristics, its effect on sperm molecular health is not thoroughly understood. The present study applied next-generation sequencing to investigate the effect of cryopreservation on the sperm transcriptomic composition of bull spermatozoa. While freshly ejaculated bull spermatozoa showed 14,280 transcripts, cryopreserved spermatozoa showed only 12,375 transcripts. Comparative analysis revealed that 241 genes were upregulated, 662 genes were downregulated, and 215 genes showed neutral expression in cryopreserved spermatozoa compared to fresh spermatozoa. Gene ontology analysis indicated that the dysregulated transcripts were involved in nucleic acid binding, transcription-specific activity, and protein kinase binding involving protein autophosphorylation, ventricular septum morphogenesis, and organ development. Moreover, the dysregulated genes in cryopreserved spermatozoa were involved in pathways associated with glycogen metabolism, MAPK signalling, embryonic organ morphogenesis, ectodermal placode formation, and regulation of protein auto-phosphorylation. These findings suggest that the cryopreservation process induced alterations in the abundance of sperm transcripts related to potential fertility-associated functions and pathways, which might partly explain the reduced fertility observed with cryopreserved bull spermatozoa.

Bi-allelic variants in human TCTE1/DRC5 cause asthenospermia and male infertility

Asthenozoospermia (AZS) is a common male infertility phenotype, accounting for 18% of infertile patients. The N-DRC (Nexin-dynein Regulatory Complex) complex is the motor regulating device in the flagellum, which is found in most eukaryotic organisms with flagellum. The deletion of TCTE1 (T-Complex-Associated Testis-Expressed 1), a component of the N-DRC complex also known as DRC5 (Dynein regulatory complex subunit 5), has been shown to cause asthenospermia in mice. This study mainly introduces a clinical case of male infertility with normal sperm count, normal morphological structure, but low motility and weak forward movement. By whole-exome sequencing, we found that TCTE1 became a frameshift mutant, ENST00000371505.5: c.396_397insTC (p.Arg133Serfs*33), resulting in the rapid degradation of TCTE1 protein and male infertility. This phenotype is similar to the Tcte1^-/- (Tcte1 knockout) mice, which showed structural integrity but reduced motility. Further, different from mice, in vitro Fertilization (IVF) could successfully solve the patient's problem of infertility. Our data provides a better understanding of the biological functions of TCTE1 in human flagellum assembly and male fertility.

Broadening INPP5E phenotypic spectrum: detection of rare variants in syndromic and non-syndromic IRD

Pathogenic variants in INPP5E cause Joubert syndrome (JBTS), a ciliopathy with retinal involvement. However, despite sporadic cases in large cohort sequencing studies, a clear association with non-syndromic inherited retinal degenerations (IRDs) has not been made. We validate this association by reporting 16 non-syndromic IRD patients from ten families with bi-allelic mutations in INPP5E. Additional two patients showed early onset IRD with limited JBTS features. Detailed phenotypic description for all probands is presented. We report 14 rare INPP5E variants, 12 of which have not been reported in previous studies. We present tertiary protein modeling and analyze all INPP5E variants for deleteriousness and phenotypic correlation. We observe that the combined impact of INPP5E variants in JBTS and non-syndromic IRD patients does not reveal a clear genotype-phenotype correlation, suggesting the involvement of genetic modifiers. Our study cements the wide phenotypic spectrum of INPP5E disease, adding proof that sequence defects in this gene can lead to early-onset non-syndromic IRD.

Deciphering the complexity of sperm transcriptome reveals genes governing functional membrane and acrosome integrities potentially influence fertility

Deciphering sperm transcriptome is the key to understanding the molecular mechanisms governing peri-fertilization, embryonic development, and pregnancy establishment. This study aimed to profile sperm transcriptome to identify signature transcripts regulating male fertility. Semen samples were collected from 47 bulls with varied fertility rates. The sperm total RNA was isolated (n = 8) and subjected to transcriptome sequencing. Based on the expression pattern obtained from RNA profiling, the bulls were grouped (p = 0.03) into high-fertile and sub-fertile, and signature transcripts controlling sperm functions and fertility were identified. The results were validated using the OMIM database, qPCR, and sperm function tests. The sperm contains 1100 to 1700 intact transcripts, of which BCL2L11 and CAPZA3 were abundant and associated (p < 0.05) with spermatogenesis and post-embryonic organ morphogenesis. The upregulated genes in the acrosome integrity and functional membrane integrity groups had a close association with the fertility rate. The biological functions of these upregulated genes (p < 0.05) in the high-fertile bulls were associated with spermatogenesis (AFF4 and BRIP1), sperm motility (AK6 and ATP6V1G3), capacitation and zona binding (AGFG1), embryo development (TCF7 and AKIRIN2), and placental development (KRT19). The transcripts involved in pathways regulating embryonic development such as translation (EEF1B2 and MTIF3, p = 8.87E-05) and nonsense-mediated decay (RPL23 and RPL7A, p = 5.01E-27) were upregulated in high-fertile bulls. The identified transcripts may significantly impact oocyte function, embryogenesis, trophectoderm development, and pregnancy establishment. In addition, the study also reveals that the genes governing sperm functional membrane integrity and acrosome integrity have a prospective effect on male fertility.

The Novel Key Genes of Non-obstructive Azoospermia Affect Spermatogenesis: Transcriptomic Analysis Based on RNA-Seq and scRNA-Seq Data

Non-obstructive azoospermia (NOA) is one of the most important causes of male infertility. It is mainly characterized by the absence of sperm in semen repeatedly or the number of sperm is small and not fully developed. At present, its pathogenesis remains largely unknown. The goal of this study is to identify hub genes that might affect biomarkers related to spermatogenesis. Using the clinically significant transcriptome and single-cell sequencing data sets on the Gene Expression Omnibus (GEO) database, we identified candidate hub genes related to spermatogenesis. Based on them, we performed Gene Ontology (GO) functional enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment pathway analyses, protein-protein interaction (PPI) network analysis, principal component analysis (PCA), cell cluster analysis, and pseudo-chronological analysis. We identified a total of 430 differentially expressed genes, of which three have not been reported related to spermatogenesis (C22orf23, TSACC, and TTC25), and the expression of these three hub genes was different in each type of sperm cells. The results of the pseudo-chronological analysis of the three hub genes indicated that TTC25 was in a low expression state during the whole process of sperm development, while the expression of C22orf23 had two fluctuations in the differentiating spermatogonia and late primary spermatocyte stages, and TSACC showed an upward trend from the spermatogonial stem cell stage to the spermatogenesis stage. Our research found that the three hub genes were different in the trajectory of sperm development, indicating that they might play important roles in different sperm cells. This result is of great significance for revealing the pathogenic mechanism of NOA and further research.

AutoMap is a high performance homozygosity mapping tool using next-generation sequencing data

Homozygosity mapping is a powerful method for identifying mutations in patients with recessive conditions, especially in consanguineous families or isolated populations. Historically, it has been used in conjunction with genotypes from highly polymorphic markers, such as DNA microsatellites or common SNPs. Traditional software performs rather poorly with data from Whole Exome Sequencing (WES) and Whole Genome Sequencing (WGS), which are now extensively used in medical genetics. We develop AutoMap, a tool that is both web-based or downloadable, to allow performing homozygosity mapping directly on VCF (Variant Call Format) calls from WES or WGS projects. Following a training step on WES data from 26 consanguineous families and a validation procedure on a matched cohort, our method shows higher overall performances when compared with eight existing tools. Most importantly, when tested on real cases with negative molecular diagnosis from an internal set, AutoMap detects three gene-disease and multiple variant-disease associations that were previously unrecognized, projecting clear benefits for both molecular diagnosis and research activities in medical genetics.

Homozygosity mapping is a useful tool for identifying candidate mutations in recessive conditions, however application to next generation sequencing data has been sub-optimal. Here, the authors present AutoMap, which efficiently identifies runs of homozygosity in whole exome/genome sequencing data.

New clinical and molecular evidence linking mutations in ARSG to Usher syndrome type IV

In murine and canine animal models, mutations in the Arylsulfatase G gene (ARSG) cause a particular lysosomal storage disorder characterized by neurological phenotypes. Recently, two variants in the same gene were found to be associated with an atypical form of Usher syndrome in humans, leading to visual and auditory impairment without the involvement of the central nervous system. In this study, we identified three novel pathogenic variants in ARSG, which segregated recessively with the disease in two families from Portugal. The probands were affected with retinitis pigmentosa and sensorineural hearing loss, generally with an onset of symptoms in their fourth decade of life. Functional experiments showed that these pathogenic variants abolish the sulfatase activity of the Arylsulfatase G enzyme and impede the appropriate lysosomal localization of the protein product, which appears to be retained in the endoplasmic reticulum. Our data enable to definitely confirm that different biallelic variants in ARSG cause a specific deaf-blindness syndrome, by abolishing the activity of the enzyme it encodes.

Genetic underpinnings of asthenozoospermia

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

scAPAtrap: identification and quantification of alternative polyadenylation sites from single-cell RNA-seq data

Alternative polyadenylation (APA) generates diverse mRNA isoforms, which contributes to transcriptome diversity and gene expression regulation by affecting mRNA stability, translation and localization in cells. The rapid development of 3' tag-based single-cell RNA-sequencing (scRNA-seq) technologies, such as CEL-seq and 10x Genomics, has led to the emergence of computational methods for identifying APA sites and profiling APA dynamics at single-cell resolution. However, existing methods fail to detect the precise location of poly(A) sites or sites with low read coverage. Moreover, they rely on priori genome annotation and can only detect poly(A) sites located within or near annotated genes. Here we proposed a tool called scAPAtrap for detecting poly(A) sites at the whole genome level in individual cells from 3' tag-based scRNA-seq data. scAPAtrap incorporates peak identification and poly(A) read anchoring, enabling the identification of the precise location of poly(A) sites, even for sites with low read coverage. Moreover, scAPAtrap can identify poly(A) sites without using priori genome annotation, which helps locate novel poly(A) sites in previously overlooked regions and improve genome annotation. We compared scAPAtrap with two latest methods, scAPA and Sierra, using scRNA-seq data from different experimental technologies and species. Results show that scAPAtrap identified poly(A) sites with higher accuracy and sensitivity than competing methods and could be used to explore APA dynamics among cell types or the heterogeneous APA isoform expression in individual cells. scAPAtrap is available at https://github.com/BMILAB/scAPAtrap.

The Male Is Significantly Implicated as the Cause of Unexplained Infertility

Male infertility is recognized as a relatively common, complex condition, generated by a broad array of environmental and genetic factors. Historical reliance on the conventional semen profile has tended to underestimate the true contribution of "the male factor" to human infertility. This review highlights the importance of genetic and epigenetic factors in the etiology of male infertility, identifying a range of mutations responsible for primary testicular failure and impaired fertilizing potential. More than three quarters of all de novo mutations arise in the male germline via mechanisms that involve the inefficient or defective repair of DNA damage. Understanding the range of factors capable of creating genetic turmoil in the paternal germline is essential, if we are to gain a deep understanding of the causes of male infertility, rather than just the symptoms that characterize its presence. High levels of DNA fragmentation induced by oxidative stress are part of this equation. Oxidative stress is, in turn, driven by biological (age, ejaculation frequency, varicocele, infection), lifestyle (smoking, obesity), and environmental factors (heat, other forms of electromagnetic radiation, and toxins) that can impair the fertilizing potential of the spermatozoa and influence the incidence of spontaneous mutations that may cause infertility in the offspring.

Motile cilia genetics and cell biology: big results from little mice

Our understanding of motile cilia and their role in disease has increased tremendously over the last two decades, with critical information and insight coming from the analysis of mouse models. Motile cilia form on specific epithelial cell types and typically beat in a coordinated, whip-like manner to facilitate the flow and clearance of fluids along the cell surface. Defects in formation and function of motile cilia result in primary ciliary dyskinesia (PCD), a genetically heterogeneous disorder with a well-characterized phenotype but no effective treatment. A number of model systems, ranging from unicellular eukaryotes to mammals, have provided information about the genetics, biochemistry, and structure of motile cilia. However, with remarkable resources available for genetic manipulation and developmental, pathological, and physiological analysis of phenotype, the mouse has risen to the forefront of understanding mammalian motile cilia and modeling PCD. This is evidenced by a large number of relevant mouse lines and an extensive body of genetic and phenotypic data. More recently, application of innovative cell biological techniques to these models has enabled substantial advancement in elucidating the molecular and cellular mechanisms underlying the biogenesis and function of mammalian motile cilia. In this article, we will review genetic and cell biological studies of motile cilia in mouse models and their contributions to our understanding of motile cilia and PCD pathogenesis.

New insights into the potential mechanisms of spermatogenic failure in patients with idiopathic azoospermia

Idiopathic azoospermia (IA) refers to azoospermia without a clear aetiology. Due to the unclear aetiology and pathological mechanism of IA, there is no effective treatment for IA. The development of assisted reproductive and microsperm extraction technologies has brought hope to patients with IA with fertility problems. However, there are still many patients with IA whose testes lack healthy sperm, causing infertility. Therefore, it is key to identify how testicular spermatogenic failure can be reversed to promote spermatogenesis in patients with IA to resolve fertility problems; these goals are a great challenge in reproductive medicine. The underlying genetic factors seem to be important pathological factors of IA. Understanding the role of genetic factors in the pathological mechanism of spermatogenic failure in patients with IA is of great value for future studies and treatments and is also an important reference for the reproductive health of males and their offspring. A method combining sequencing technology and bioinformatics analysis is an important means to understand the genetic pathological mechanisms. We used bioinformatics analysis to study the public human IA dataset. We found that the pathogenic mechanism of IA may be related to abnormal ciliary structure and function and disrupted RNA metabolism in spermatogenic cells. Disrupted m6A regulation of spermatogenesis may be an important pathological mechanism of IA and warrants attention. Finally, we screened for key genes and potential therapeutic drugs to determine future research directions.

The Role of Genetics and Oxidative Stress in the Etiology of Male Infertility-A Unifying Hypothesis?

Despite the high prevalence of male infertility, very little is known about its etiology. In recent years however, advances in gene sequencing technology have enabled us to identify a large number of rare single point mutations responsible for impeding all aspects of male reproduction from its embryonic origins, through the endocrine regulation of spermatogenesis to germ cell differentiation and sperm function. Such monogenic mutations aside, the most common genetic causes of male infertility are aneuploidies such as Klinefelter syndrome and Y-chromosome mutations which together account for around 20-25% of all cases of non-obstructive azoospermia. Oxidative stress has also emerged as a major cause of male fertility with at least 40% of patients exhibiting some evidence of redox attack, resulting in high levels of lipid peroxidation and oxidative DNA damage in the form of 8-hydroxy-2'-deoxyguanosine (8OHdG). The latter is highly mutagenic and may contribute to de novo mutations in our species, 75% of which are known to occur in the male germ line. An examination of 8OHdG lesions in the human sperm genome has revealed ~9,000 genomic regions vulnerable to oxidative attack in spermatozoa. While these oxidized bases are generally spread widely across the genome, a particular region on chromosome 15 appears to be a hot spot for oxidative attack. This locus maps to a genetic location which has linkages to male infertility, cancer, imprinting disorders and a variety of behavioral conditions (autism, bipolar disease, spontaneous schizophrenia) which have been linked to the age of the father at the moment of conception. We present a hypothesis whereby a number of environmental, lifestyle and clinical factors conspire to induce oxidative DNA damage in the male germ line which then triggers the formation de novo mutations which can have a major impact on the health of the offspring including their subsequent fertility.