Evidence from enzymatic and meta-analyses does not support a direct association between USP26 gene variants and male infertility

Clinical detection, diagnosis and treatment of morphological abnormalities of sperm flagella: A review of literature

Sperm carries male genetic information, and flagella help move the sperm to reach oocytes. When the ultrastructure of the flagella is abnormal, the sperm is unable to reach the oocyte and achieve insemination. Multiple morphological abnormalities of sperm flagella (MMAF) is a relatively rare idiopathic condition that is mainly characterized by multiple defects in sperm flagella. In the last decade, with the development of high-throughput DNA sequencing approaches, many genes have been revealed to be related to MMAF. However, the differences in sperm phenotypes and reproductive outcomes in many cases are attributed to different pathogenic genes or different pathogenic mutations in the same gene. Here, we will review information about the various phenotypes resulting from different pathogenic genes, including sperm ultrastructure and encoding proteins with their location and functions as well as assisted reproductive technology (ART) outcomes. We will share our clinical detection and diagnosis experience to provide additional clinical views and broaden the understanding of this disease.

Novel Mutations in X-Linked, USP26-Induced Asthenoteratozoospermia and Male Infertility

Male infertility is a multifactorial disease with a strong genetic background. Abnormal sperm morphologies have been found to be closely related to male infertility. Here, we conducted whole-exome sequencing in a cohort of 150 Han Chinese men with asthenoteratozoospermia. Two novel hemizygous mutations were identified in USP26, an X-linked gene preferentially expressed in the testis and encoding a deubiquitinating enzyme. These USP26 variants are extremely rare in human population genome databases and have been predicted to be deleterious by multiple bioinformatics tools. Hematoxylin-eosin staining and electron microscopy analyses of the spermatozoa from men harboring hemizygous USP26 variants showed a highly aberrant morphology and ultrastructure of the sperm heads and flagella. Real-time quantitative PCR and immunoblotting assays revealed obviously reduced levels of USP26 mRNA and protein in the spermatozoa from men harboring hemizygous deleterious variants of USP26. Furthermore, intracytoplasmic sperm injections performed on infertile men harboring hemizygous USP26 variants achieved satisfactory outcomes. Overall, our study demonstrates that USP26 is essential for normal sperm morphogenesis, and hemizygous USP26 mutations can induce X-linked asthenoteratozoospermia. These findings will provide effective guidance for the genetic and reproductive counseling of infertile men with asthenoteratozoospermia.

Paternal USP26 mutations raise Klinefelter syndrome risk in the offspring of mice and humans

Current understanding holds that Klinefelter syndrome (KS) is not inherited, but arises randomly during meiosis. Whether there is any genetic basis for the origin of KS is unknown. Here, guided by our identification of some USP26 variations apparently associated with KS, we found that knockout of Usp26 in male mice resulted in the production of 41, XXY offspring. USP26 protein is localized at the XY body, and the disruption of Usp26 causes incomplete sex chromosome pairing by destabilizing TEX11. The unpaired sex chromosomes then result in XY aneuploid spermatozoa. Consistent with our mouse results, a clinical study shows that some USP26 variations increase the proportion of XY aneuploid spermatozoa in fertile men, and we identified two families with KS offspring wherein the father of the KS patient harbored a USP26-mutated haplotype, further supporting that paternal USP26 mutation can cause KS offspring production. Thus, some KS should originate from XY spermatozoa, and paternal USP26 mutations increase the risk of producing KS offspring.

A novel frameshift mutation in ubiquitin-specific protease 26 gene in a patient with severe oligozoospermia

Ubiquitin-specific protease 26 (USP26) encodes a predicted protein containing his- and cys- domains that are conserved among deubiquitinating enzymes. USP26 is specifically expressed in testis tissue and is a potential infertility gene. In the present study, we performed genetic testing related to spermatogenesis impairment in a patient with idiopathic severe oligozoospermia to identify the cause. The patient underwent clinical examination and reproductive hormone testing. Genes associated with male infertility, including USP26, were assessed by targeted exome sequencing. A novel frameshift mutation, c.2195delT (p.Phe732Serfs*14), was identified in USP26. This frameshift mutation was located in residue 732 of USP26 gene, leading to loss of the conserved deubiquitinating enzyme His-domain and producing a truncated protein of 744 amino acids. Bioinformatics analysis revealed this mutation to be pathogenic. A novel framshift mutation c.2195delT (p.Phe732Serfs*14) in USP26 gene was reported to be associated with male infertility in a Chinese patient with severe oligozoospermia.

Disruption of ubiquitin specific protease 26 gene causes male subfertility associated with spermatogenesis defects in mice†

Ubiquitin-specific protease 26 (USP26) is an X-linked gene exclusively expressed in the testis and codes for the USP26, a peptidase enzyme that belongs to the deubiquitinating enzyme family. Recent studies have indicated that mutations in USP26 affect spermatogenesis and are associated with male infertility in humans and mice. However, the exact role of USP26 in spermatogenesis and how it affects male reproduction remains unknown. In this study, we generated a conventional Usp26 knockout mouse model and found that deletion of Usp26 in male mice (Usp26-/Y) leads to significantly reduced pup numbers per litter and significantly increased intervals between two consecutive offspring. We also found that the serum follicle stimulating hormone and testosterone levels of adult Usp26-/Y mice were significantly decreased compared to those of Usp26+/Y mice. Histological examination results showed that Usp26-/Y mice had significantly increased percentage of abnormal seminiferous tubules at different ages. Flow cytometry results exhibited that Usp26-/Y mice had significantly reduced percentage of mature haploid cells in the testes compared to Usp26+/Y mice. Sperm counts in epididymis were also significantly declined in Usp26-/Y mice compared to those in Usp26+/Y mice. Immunohistochemistry and immunofluorescence staining and immunoprecipitation analysis results showed that USP26 and androgen receptor were co-localized in mouse testicular cells at different ages and they both had physiological interactions. All these results demonstrated that the loss of Usp26 affects spermatogenesis and hormone secretion and causes male subfertility. Our study also provides the evidence on the interactions between USP26 and androgen receptor in mouse testis, whereby pointing to a potential mechanism.

Novel mutation in USP26 associated with azoospermia in a Sertoli cell-only syndrome patient

Background

Ubiquitin‐Specific Peptidase 26 (USP26), located on the X chromosome, encodes a deubiquitinating enzyme expressed mainly in testis, where it regulates protein turnover during spermatogenesis and modulates the ubiquitination levels of the Androgen Receptor (AR), and as a consequence, affects AR signaling.

Methods

The patient was thoroughly characterized clinically. He was genetically tested by chromosome analysis and whole exome sequencing (WES).

Results

The patient was diagnosed with Sertoli cell‐only syndrome pattern (SCOS). The WES analysis revealed only the variation in USP26: causing p.P469S in a highly evolutionary conserved amino acid as the possible cause for SCOS. The literature search identified 34 single variations and 14 clusters of variations in USP26 that were associated with male infertility. Only one of the 22 variations and of one cluster of three mutations tested for ubiquitination activity was found as damaging. Only one out of six variations tested for effect on AR function was found as damaging. Thus, the association of USP26 with male fertility was questioned.

Conclusions

The finding in our patient and the discussion on the reviewed literature support a possible role for USP26 in male fertility.

The X chromosome and male infertility

The X chromosome is a key player in germ cell development, as has been highlighted for males in previous studies revealing that the mammalian X chromosome is enriched in genes expressed in early spermatogenesis. In this review, we focus on the X chromosome’s unique biology as associated with human male infertility. Male infertility is most commonly caused by spermatogenic defects to which X chromosome dosage is closely linked; for example, any supernumerary X chromosome as in Klinefelter syndrome will lead to male infertility. Furthermore, because males normally only have a single X chromosome and because X-linked genetic anomalies are generally only present in a single copy in males, any loss-of-function mutations in single-copy X-chromosomal genes cannot be compensated by a normal allele. These features make X-linked genes particularly attractive for studying male spermatogenic failure. However, to date, only very few genetic causes have been identified as being definitively responsible for male infertility in humans. Although genetic studies of germ cell-enriched X-chromosomal genes in mice suggest a role of certain human orthologs in infertile men, these genes in mice and humans have striking evolutionary differences. Furthermore, the complexity and highly repetitive structure of the X chromosome hinder the mutational analysis of X-linked genes in humans. Therefore, we conclude that additional methodological approaches are urgently warranted to advance our understanding of the genetics of X-linked male infertility.

Usp26 mutation in mice leads to defective spermatogenesis depending on genetic background

Spermatogenesis is a reproductive system process that produces sperm. Ubiquitin specific peptidase 26 (USP26) is an X chromosome-linked deubiquitinase that is specifically expressed in the testes. It has long been controversial whether USP26 variants are associated with human male infertility. Thus, in the present study, we introduced a mutation into the Usp26 gene in mice and found that Usp26 mutant males backcrossed to a DBA/2 background, but not a C57BL/6 background, were sterile or subfertile and had atrophic testes. These findings indicate that the effects of the Usp26 mutation on male reproductive capacity were influenced by genetic background. Sperm in the cauda epididymis of Usp26 mutant mice backcrossed to a DBA/2 background were decreased in number and showed a malformed head morphology compared to those of wild-type mice. Additionally, histological examinations of the testes revealed that the number of round and elongated spermatids were dramatically reduced in Usp26 mutant mice. The mutant mice exhibited unsynapsed chromosomes in pachynema and defective chiasma formation in diplonema, which presumably resulted in apoptosis of metaphase spermatocytes and subsequent decrease of spermatids. Taken together, these results indicate that the deficiencies in fertility and spermatogenesis caused by mutation of Usp26 were dependent on genetic background.

Ubiquitin-specific protease 26 (USP26) is not essential for mouse gametogenesis and fertility

Ubiquitin-specific protease 26 (USP26) is a deubiquitylating enzyme belonging to the USPs family with a transcription pattern restricted to the male germline. Since protein ubiquitination is an essential regulatory mechanism during meiosis, many efforts have been focused on elucidating the function of USP26 and its relationship with fertility. During the last decade, several studies have reported the presence of different polymorphisms in USP26 in patients with non-obstructive azoospermia (NOA) or severe oligozoospermia suggesting that this gene may be associated with human infertility. However, other studies have revealed the presence of these and novel polymorphisms, including nonsense mutations, in men with normal spermatogenesis as well. Thus, the results remain controversial and its function is unknown. In the present study, we describe the in vivo functional analysis of mice lacking USP26. The phenotypic analysis of two different Usp26-null mutants showed no overt-phenotype with both males and females being fertile. Cytological analysis of spermatocytes showed no defects in synapsis, chromosome dynamics, DNA repair, or recombination. Histopathological analysis revealed a normal distribution and number of the different cell types in both male and female mice. Finally, normal counts were observed in fertility assessments. These results represent the first in vivo evidence showing that USP26 is not essential for mouse gametogenesis.

TGF-β signaling pathway mediated by deubiquitinating enzymes

Ubiquitination is a reversible cellular process mediated by ubiquitin-conjugating enzymes, whereas deubiquitinating enzymes (DUBs) detach the covalently conjugated ubiquitin from target substrates to counter ubiquitination. DUBs play a crucial role in regulating various signal transduction pathways and biological processes including apoptosis, cell proliferation, DNA damage repair, metastasis, differentiation, etc. Since the transforming growth factor-β (TGF-β) signaling pathway participates in various cellular functions such as inflammation, metastasis and embryogenesis, aberrant regulation of TGF-β signaling induces abnormal cellular functions resulting in numerous diseases. This review focuses on DUBs regulating the TGF-β signaling pathway. We discuss the molecular mechanisms of DUBs involved in TGF-β signaling pathway, and biological and therapeutic implications for various diseases.

Analysis of Parent-of-Origin Effects on the X Chromosome in Asian and European Orofacial Cleft Triads Identifies Associations with DMD, FGF13, EGFL6, and Additional Loci at Xp22.2

Background: Although both the mother's and father's alleles are present in the offspring, they may not operate at the same level. These parent-of-origin (PoO) effects have not yet been explored on the X chromosome, which motivated us to develop new methods for detecting such effects. Orofacial clefts (OFCs) exhibit sex-specific differences in prevalence and are examples of traits where a search for various types of effects on the X chromosome might be relevant. Materials and Methods: We upgraded our R-package Haplin to enable genome-wide analyses of PoO effects, as well as power simulations for different statistical models. 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European case-parent triads of isolated OFCs were available from a previous GWAS. For each ethnicity, cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO) were analyzed separately using two X-inactivation models and a sliding-window approach to haplotype analysis. In addition, we performed analyses restricted to female offspring. Results: Associations were identified in "Dystrophin" (DMD, Xp21.2-p21.1), "Fibroblast growth factor 13" (FGF13, Xq26.3-q27.1) and "EGF-like domain multiple 6" (EGFL6, Xp22.2), with biologically plausible links to OFCs. Unlike EGFL6, the other associations on chromosomal region Xp22.2 had no apparent connections to OFCs. However, the Xp22.2 region itself is of potential interest because it contains genes for clefting syndromes [for example, "Oral-facial-digital syndrome 1" (OFD1) and "Midline 1" (MID1)]. Overall, the identified associations were highly specific for ethnicity, cleft subtype and X-inactivation model, except for DMD in which associations were identified in both CPO and CL/P, in the model with X-inactivation and in Europeans only. Discussion/Conclusion: The specificity of the associations for ethnicity, cleft subtype and X-inactivation model underscores the utility of conducting subanalyses, despite the ensuing need to adjust for additional multiple testing. Further investigations are needed to confirm the associations with DMD, EGF16, and FGF13. Furthermore, chromosomal region Xp22.2 appears to be a hotspot for genes implicated in clefting syndromes and thus constitutes an exciting direction to pursue in future OFCs research. More generally, the new methods presented here are readily adaptable to the study of X-linked PoO effects in other outcomes that use a family-based design.

The impacts of nineteen mutations on the enzymatic activity of USP26

OBJECTIVE

The association between mutations in the USP26 gene and male infertility has been studied intensively. However, the biological function of the mutant proteins remains to be elucidated. To confirm the effects of the reported mutations, we analyse the enzyme activity of USP26 between the wild-type and the variants from a molecular perspective.

METHODS

Using pGEX-USP26 as a template, site-directed mutagenesis was conducted to generate nineteen USP26 mutant plasmids. Using Ub-Met-β-gal and GST-Ub52 as model substrates, a USP cleavage assay was conducted to assess the enzymatic activities of the mutants.

RESULTS

The enzyme activity of the Q156H mutant disappeared, but the other 18 mutants had the same activity as the wild type. E174# and E189# were terminal mutants, but they still had the same activity as the wild type. When we constructed the transcription terminal mutants E174#(1-522 bp), E174#(523-2742 bp), E189#(1-567 bp) and E189#(568-2742 bp) artificially, the enzyme activity of these four mutants disappeared.

CONCLUSIONS

We have successfully constructed nineteen mutants of USP26. The enzyme activity of the Q156H mutant disappeared, but the enzyme activities of the other 18 mutants were the same as that of the wild type.

eNOS gene T786C, G894T and 4a4b polymorphisms and male infertility susceptibility: a meta-analysis

The association between polymorphism of eNOS and male infertility in several studies was controversial. To explore a more precise estimation of the association, a meta-analysis of eight case-control studies, including 1,968 cases and 1,539 controls, were selected. The meta-analysis was conducted by calculating the pooled odds ratio (OR) with a 95% confidence interval (95% CI). Overall, the association between T786C and risk of male infertility was obvious (TC vs. TT: OR, 1.20; 95% CI, 1.01-1.42; CC vs. TT: OR, 3.37; 95% CI, 1.65-6.87; TC/CC vs. TT: OR, 1.47; 95% CI, 1.25-1.73; CC vs.

TT/TC

OR, 3.18; 95% CI, 1.54-6.56; TC vs. TT: OR, 1.65; 95% CI, 1.27-2.03). However, no overall association was observed between the other two polymorphisms of eNOS (G894T and 4a4b) and male infertility. Stratified analysis showed that significantly strong association between T786C polymorphism and semen quality was present in all three types of male infertility (azoospermia, oligozoospermia and asthenozoospermia). In the subgroup analysis based on ethnicity, both T786C and 4a4b could influence the risk of male infertility in Asian and Caucasian. Further studies of polymorphisms of eNOS with their biological functions are needed to understand the role in the development of male infertility.

Single nucleotide polymorphisms of USP26 in azoospermic men

Some studies have focused on the association between male infertility and single nucleotide polymorphisms (SNPs) in the ubiquitin-specific protease 26 (USP26) gene, but the results are controversial. In this case-control study including both normozoospermic men and patients with nonobstructive azoospermia, we analyzed both the entire coding region and 5' and 3' untranslated regions of USP26 in order to identify genetic variants in this gene to investigate the role of USP26 on spermatogenesis. We reported variations in the USP26 gene sequence in 82% of azoospermic and in 50% normospermic men. The synonymous variation c.576G>A has a frequency significantly different in the azoospermic (60.2%) and normozoospermic (23.6%) groups, while the frequencies in the two groups of both c.1090C>T and c.1737G>A missense mutations did not reach statistical significance. A cluster mutation (c.371insACA, c.494T>C) was detected in 2 normozoospermic men (2.7%). In the 5'UTR we identified the -33C>T variation both in azoospermic (3.8%) and in normozoospermic (2.7%) men. In a normozoospermic man we detected the nonsense mutation c.882C>A, never reported to date. According to our results, we suggest that only the variation c.576G>A has a frequency significantly different in azoospermic compared to normozoospermic men. Moreover, the identification in a normozoospermic man of a nonsense mutation (c.882C>A) which causes the production of a truncated protein, suggests a marginal role of USP26 in male spermatogenesis. Additional studies may be useful as we cannot exclude that the other SNPs may represent risk factors for male fertility acting by an oligogenic/polygenic mechanism.

A Novel Missense Mutation in USP26 Gene Is Associated With Nonobstructive Azoospermia

OBJECTIVE

The aim of this study was to evaluate whether ubiquitin-specific peptidase 26 (USP26) gene variations were associated with nonobstructive azoospermia (NOA).

METHODS

Seven hundred and seventy-six patients diagnosed with NOA and 709 proven fertile men were included in this study. Genetic variations of infertility-related genes, including USP26, were identified by selected exonic sequencing. The effects of USP26 mutations on androgen receptor (AR) binding, ubiquitination, and transcriptional activity were detected by immunoprecipitation and luciferase assay in Hela and TM4 cells.

RESULTS

Six novel missense mutations and 1 novel synonymous mutation of USP26 unique to the patients with NOA were identified. Of these missense mutations, USP26 R344W remarkably reduced the binding affinity and deubiquitinating activity of USP26 to AR, thus eliminated the inhibitory effect of USP26 on transcriptional activity of AR in Hela and TM4 cells.

CONCLUSION

A novel USP26 variant p.R344W is associated with NOA probably through affecting AR function.

The role of deubiquitinating enzymes in spermatogenesis

Spermatogenesis is a complex process through which spermatogonial stem cells undergo mitosis, meiosis, and cell differentiation to generate mature spermatozoa. During this process, male germ cells experience several translational modifications. One of the major post-translational modifications in eukaryotes is the ubiquitination of proteins, which targets proteins for degradation; this enables control of the expression of enzymes and structural proteins during spermatogenesis. It has become apparent that ubiquitination plays a key role in regulating every stage of spermatogenesis starting from gonocytes to differentiated spermatids. It is understood that, where there is ubiquitination, deubiquitination by deubiquitinating enzymes (DUBs) also exists to counterbalance the ubiquitination process in a reversible manner. Normal spermatogenesis is dependent on the balanced actions of ubiquitination and deubiquitination. This review highlights the current knowledge of the role of DUBs and their essential regulatory contribution to spermatogenesis, especially during progression into meiotic phase, acrosome biogenesis, quality sperm production, and apoptosis of germ cells.