Single nucleotide polymorphisms in the protamine-1 and -2 genes of fertile and infertile human male populations

Insights into the sperm chromatin and implications for male infertility from a protein perspective

Male germ cells undergo an extreme but fascinating process of chromatin remodeling that begins in the testis during the last phase of spermatogenesis and continues through epididymal sperm maturation. Most of the histones are replaced by small proteins named protamines, whose high basicity leads to a tight genomic compaction. This process is epigenetically regulated at many levels, not only by posttranslational modifications, but also by readers, writers, and erasers, in a context of a highly coordinated postmeiotic gene expression program. Protamines are key proteins for acquiring this highly specialized chromatin conformation, needed for sperm functionality. Interestingly, and contrary to what could be inferred from its very specific DNA-packaging function across protamine-containing species, human sperm chromatin contains a wide spectrum of protamine proteoforms, including truncated and posttranslationally modified proteoforms. The generation of protamine knock-out models revealed not only chromatin compaction defects, but also collateral sperm alterations contributing to infertile phenotypes, evidencing the importance of sperm chromatin protamination toward the generation of a new individual. The unique features of sperm chromatin have motivated its study, applying from conventional to the most ground-breaking techniques to disentangle its peculiarities and the cellular mechanisms governing its successful conferment, especially relevant from the protein point of view due to the important epigenetic role of sperm nuclear proteins. Gathering and contextualizing the most striking discoveries will provide a global understanding of the importance and complexity of achieving a proper chromatin compaction and exploring its implications on postfertilization events and beyond. This article is categorized under: Reproductive System Diseases > Genetics/Genomics/Epigenetics Reproductive System Diseases > Molecular and Cellular Physiology.

Impact of tobacco smoking in association with H2BFWT, PRM1 and PRM2 genes variants on male infertility

Tobacco's genotoxic components can cause a wide range of gene defects in spermatozoa such as single- or double-strand DNA breaks, cross-links, DNA-adducts, higher frequencies of aneuploidy and chromosomal abnormalities. The aim in this study was to determine the correlation between sperm quality determined by standard parameters, sperm DNA maturity tested by Chromomycin A3 (CMA3) staining, sperm DNA fragmentation tested by TUNEL assay and tobacco smoking in association with the single nucleotides polymorphisms (SNP) of three nuclear protein genes in spermatozoa (H2BFWT, PRM1 and PRM2). In this study, semen samples of 167 male patients were collected and divided into 54 non-smokers and 113 smokers. The target sequences in the extracted sperm DNA were amplified by PCR followed by Sanger sequencing. The results showed the presence of three variants: rs7885967, rs553509 and rs578953 in H2BFWT gene in the study population. Only one variant rs737008 was detected in PRM1 gene, and three variants were detected in the PRM2 gene: rs2070923, rs1646022 and rs424908. No significant association was observed between the concentration, progressive motility, morphology and the occurrence of H2BFWT, PRM1 and PRM2 SNPs. However, sperm parameters were significantly lower in heavy smokers compared to controls (p < 0.01) (sperm count: 46.00 vs. 78.50 mill/ml, progressive motility: 15.00% vs. 22.00%, and morphology 4.00% vs. 5.00%, respectively). Moreover, the heavy smoker individuals exhibited a considerable increase in CMA3 positivity and sDF compared to non-smokers (p < 0.01) (29.50% vs. 20.50% and 24.50% vs. 12.00%, respectively). In conclusion, smoking altered sperm parameters and sperm DNA integrity, but did not show a linkage with genetic variants in H2BFWT, and protamine genes (PRM1 and PRM2).

Polymorphisms in the HSF2, LRRC6, MEIG1 and PTIP genes correlate with sperm motility in idiopathic infertility

The aim of this study was to investigate the association of 24 functionally important single nucleotide polymorphisms (SNPs) with male infertility. In this cross-sectional study, we genotyped 24 functionally important single nucleotide polymorphisms in 24 infertility candidate genes in 500 oligo-/astheno-/oligoastheno-/normo-zoospermic infertile men with idiopathic infertility. Sequenom iPlex gold assay was used for genotyping. Sperm count and motility were compared between prevalent genotypes at each test locus. We did not observe any significant difference in the average sperm count between the alternate genotypes for the loci in the KLK3, LRRC6, MEIG1, HSF2, ESR2 and PTIP genes. However, we observed a significant difference in sperm motility between the alternate genotypes for the loci in the LRRC6, MEIG1, HSF2 and PTIP genes. Polymorphisms in the LRRC6 (rs200321595), MEIG1 (rs150031795), HSF2 (rs143986686) and PTIP (rs61752013) genes show association with sperm motility.

High throughput deep proteomic analysis of seminal plasma from stallions with contrasting semen quality

Seminal plasma proteins and pathways associated with sperm motility have not been elucidated in stallions. Therefore, in the current study, using the high throughput LC/MS-MS approach, we profiled stallion seminal plasma proteins and identified the proteins and pathways associated with sperm motility. Seminal plasma from six stallions producing semen with contrasting sperm motility (n = 3 each high-and low-motile group) was utilized for proteomic analysis. We identified a total of 1687 proteins in stallion seminal plasma, of which 1627 and 1496 proteins were expressed in high- (HM) and low- motile (LM) sperm of stallions, respectively. A total number of 1436 proteins were co-expressed in both the groups; 191 (11%) and 60 (3.5%) proteins were exclusively detected in HM and LM groups, respectively. A total of 220 proteins were upregulated (>1-fold change) and 386 proteins were downregulated in SP from LM group stallions as compared to HM group stallions, while 830 proteins were neutrally expressed in both the groups. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed dysregulation of the important proteins related to mitochondrial function, acrosome, and sperm cytoskeleton in the seminal plasma of stallions producing ejaculates with low sperm motility. High abundance of peroxiredoxins and low abundance of seminal Chaperonin Containing TCP1 Complex (CCT) complex and Annexins indicate dysregulated oxidative metabolism, which might be the underlying etiology for poor sperm motility in LM group stallions. In conclusion, the current study identified the seminal plasma proteomic alterations associated with poor sperm motility in stallions; the results indicate that poor sperm motility in stallions could be associated with altered expression of seminal plasma proteins involved in oxidative metabolism.

Evaluation of the association between polymorphisms of PRM1 and PRM2 and the risk of male infertility: a systematic review, meta-analysis, and meta-regression

Studies have reported the genetic gives rise to male infertility. The aim of the present meta-analysis was to evaluate the association between PRM1 (rs737008 and rs2301365) and PRM2 (rs1646022 and rs2070923) polymorphisms and susceptibility to male infertility. The association between PRM1 and PRM2 polymorphisms and the risk of male infertility was evaluated using specific search terms in the Web of Science, Cochrane Library, PubMed, and Scopus databases without language restriction until January 28, 2020. The association was determined by odds ratio (OR) and 95% confidence interval (CI) on five genetic models using Review Manager 5.3 software. The funnel plot analysis and sensitivity analysis were done by the Comprehensive Meta-analysis 2.0 software. Out of 261 records retrieved from the databases, 17 studies were analyzed in the meta-analysis, including the four PRM polymorphisms. The pooled results as OR (P-value) showed 0.96 (0.44), 1.04 (0.70), 0.94 (0.51), 0.94 (0.48), and 1.03 (0.72) for PRM1 rs737008 polymorphism and 1.67 (0.0007), 1.73 (0.06), 1.50 (0.007), 1.56 (0.004), and 1.62 (0.33) for PRM1 rs2301365 polymorphism in allele, homozygous, heterozygous, recessive, and dominant models, respectively. Moreover, the pooled results as OR (P-value) showed 1.19 (0.004), 1.15 (0.26), 1.08 (0.70), 1.05 (0.76), and 0.98 (0.82) for PRM2 rs1646022 and 0.88 (0.04), 0.84 (0.10), 1.05 (0.81), 0.90 (0.24), and 0.80 (0.02) for PRM2 rs2070923 in allele, homozygous, heterozygous, recessive, and dominant models, respectively. The results showed PRM1 rs2301365 and PRM2 rs1646022 polymorphisms were associated with an elevated risk of male infertility and PRM2 rs2070923 polymorphism had a protective role in infertile men.

Genetic Polymorphisms within The Intronless ACTL7A and ACTL7B Genes Encoding Spermatogenesis-Specific Actin-Like Proteins in Japanese Males

Actins play essential roles in cellular morphogenesis. In mice, the T-actin1 and 2 genes, which encode actin-like proteins, are specifically expressed in haploid germ cells. Both T-ACTIN1/ACTLB and T-ACTIN2/ACTL7A have also been cloned and studied. The orthologous genes in humans are present on chromosome 9q31.3 as intronless genes. Defects of germ cell-specific genes can introduce infertility without somatic function impairment. We determined T- ACTIN1 and 2, specifically expressed in the testis using reverse-transcription polymerase chain reaction (RT-PCR). To examine whether genetic polymorphisms of the T-ACTIN1 and 2 genes are associated with male infertility, we screened for T-ACTIN1 and 2 polymorphisms by direct sequencing of DNA from 282 sterile and 89 fertile Japanese men. We identified five and six single nucleotide polymorphisms (SNPs) in the T-ACTIN1 and 2 regions of the sterile and fertile subjects respectively. Among these genetic polymorphisms was a novel SNP that was not in the National Center for Biotechnology Information SNP database. Although we could not determine whether these SNPs cause infertility, the prevalence of these genetic polymorphisms may be useful for analyzing polymorphisms in future large- scale genetic analyses.

The c.-190 C>A transversion in promoter region of protamine 1 gene as a genetic risk factor in Egyptian men with idiopathic infertility

Protamines are considered the most important structure in the sperm nucleus, and they are proteins with a significantly large amount of amino acids carrying a positive charge, which allows the formation of the tight package of the genomic DNA in the spermatozoa. Many authors studied the abnormalities in the protamine 1 (PRM1) and/or protamine 2 (PRM2) genes and reported their possible association with male infertility. The chromosome 16 (16p13.2) carries these genes containing multiple undiscovered single nucleotide polymorphisms. The aim of the present study was to investigate the association of c.-190 C>A transversions that occur in PRM1 with idiopathic infertility in a sample of Egyptian men. It was a case-control study, and blood samples were collected from sixty male patients complaining of idiopathic infertility and forty healthy fertile males. The c.-190 C>A transversion in promotor region protamine 1 gene (rs2301365) was assessed by 5' nuclease assay, using Rotor-Gene Q real-time PCR system. The results of the present study revealed that CA and AA genotypes in PRM1 gene were associated significantly with low sperm concentration and decreased sperm motility (p = 0.001). Cases carrying A allele had a 6.05-fold increased risk for idiopathic infertility than cases carrying the C allele (OR: 6.05, 95% CI: 2.038-17.98 p statistically significant ≤0.05). Analysis of the results revealed that the c.-190 C>A transversion may be involved in the development of male infertility.

Analysis of PRM1 and PRM2 Polymorphisms in Iranian Infertile Men with Idiopathic Teratozoospermia

Single nucleotide polymorphisms (SNPs) in a number of genes involved in sperm maturation are considered as one of the main factors for male infertility. The aim of the present case-control study was to examine the association of SNPs in protamine1 (PRM1) and protamine2 (PRM2) genes with idiopathic teratozoospermia. In this case-control study, some SNPs in PRM1 (c.49 C>T, c.102 G>T and c.230A>C) and PRM2 (rs545828790, rs115686767, rs201933708, rs2070923 and rs1646022) were investigated in 30 idiopathic infertile men with teratozoospermia (case group) in comparison with 35 fertile men (controls). Genotyping of SNPs was undertaken using polymerase chain reaction (PCR)-direct sequencing. For PRM1, c.230A>C, as a synonymous polymorphism, was detected in both teratozoo- spermic men (heterozygous n=26, homozygous minor n=1) allele frequency C(48) A(52) and controls (heterozygous n=15, homozygous minor n=4). All cases and controls were genotyped for rs545828790 in PRM2, a missense poly- morphism, as well as rs115686767 and rs201933708, both of which synonymous variants. The findings showed an intronic variant in PRM2 (rs2070923) was also present in both groups. Also, rs1646022, a missense polymorphism, occurred in teratozoospermic men (heterozygous n=10, homozygous minor n=5) and controls (heterozygous n=13, homozygous minor n=2). However, there were no significant differences in SNPs of PRM1 and PRM2 between the two groups, however, for c.230A>C, the frequency of the CA genotype was significantly higher in infertile men with teratozoospermia (P=0.001). We demonstrate that PRM2 G398C and A473C polymorphisms were associated with the teratozoospermia and its genetic variation was in relation to semen quality, sperm apoptosis, and morphology in the Iranian population. This study is a preliminary study and presenting data as part of a future comprehensive study to clinically establish whether these gene polymorphisms are biomarkers for susceptibility to teratozoospermia.

Nucleotide variability of protamine genes influencing bull sperm motility variables

Protamines (PRMs), important proteins of chromatin condensation in spermiogenesis, are promising candidate genes to explore markers of sperm motility. The coding and in-silico predicted promoter regions of these genes were investigated in 102 crossbred and 32 purebred cattle. Also, mRNA quantification was done to explore its possibility as diagnostic tool of infertility. The PCR-SSCP analysis indicated there were two band patterns only in fragment I of the PRM1 and fragment II of the PRM2 gene. The sequence analysis revealed A152G and G179A transitions in the PRM1 gene. Similarly, G35A, A49G and A64G transitions were identified in the PRM2 gene which resulted in altered amino acid sequences from arginine (R) to glutamine (Q), from arginine (R) to glycine (G) and from arginine (R) to glycine (G), respectively. This caused the reduction in molecular weight of PRM2 from 2157.66 to 1931.33 Da due to reduction in the number of basic amino acids. These altered properties of the PRM2 protein led to the reduction in Mass Motility (MM: P < 0.01), Initial Progressive Motility (IPM; P < 0.05) and Post Thaw Motility (PTM; P < 0.05) in crossbred bulls. The least squares analysis of variance indicated there was an effect of PRM2 haplotypes on MM (P = 0.0069), IPM (P = 0.0306) and PTM (P = 0.0500) in crossbred cattle and on PTM (P = 0.0408) in the overall cattle population. Based on the RT-qPCR analysis, however, there was not any significant variation of PRM1 and PRM2 gene expression among sperm of Vrindavani bulls with relatively lesser and greater sperm motility.

Systematic review and meta-analysis of the genetic association between protamine polymorphism and male infertility

While several previous studies have proposed an association between male infertility and protamine polymorphism, the reported findings have shown some inconsistency. To evaluate the potential association between the two most common single nucleotide polymorphisms (rs2301365 and rs1646022) in protamine and male infertility, we performed a meta-analysis involving 2713 cases and 2086 controls from 15 published case-controlled studies. Overall, our analysis showed significant associations between the specific protamine single-nucleotide polymorphism (rs2301365) and male infertility, and this association was indicated by all of the models we tested. Subgroup analysis revealed significant associations with a Caucasian background, PCR sequence, population-based, case size of > 150 and case size of < 150 subgroups. Similarly, significant associations were found between rs1646022 and male infertility in the hospital population and case size of < 200 subgroups. However, trial sequential analysis showed that the number of patients in the study did not reach optimal information size. Further studies with larger sample sizes are now warranted to clarify the potential roles of the two protamine polymorphisms in the pathogenesis of male infertility. This may help us to understand the precise molecular mechanisms underlying the effect of protamines upon male infertility.

Genetic Polymorphisms in PRM1, PRM2, and YBX2 Genes are Associated with Male Factor Infertility

AIMS

The etiology of infertility is still unknown in almost half of all male infertility patients. In sperm, DNA condensation differs from somatic and female gamete cells, with the protamine (PRM) gene and its transcription factor, Y-box binding protein 2 (YBX2), playing key roles in making the structure more compact. Protamine polymorphisms have been studied in different populations, but various results have been acquired.

MATERIALS AND METHODS

In our study, we examined, for the first time in a Turkish population, the association between protamine gene alleles (PRM1 c.-190C>A, PRM1 c.197G>T, and PRM2 c.248C>T), and YBX2 (c.187T>C and c.1095 + 16A>G) and male infertility. This was accomplished using polymerase chain reaction-restriction fragment length polymorphism analyses of 100 infertile and 100 fertile Turkish men. Sperm DNA fragmentation analysis was performed using the Comet technique.

RESULTS

We found that the AA and CA genotypes of the PRM1 c.-190C>A polymorphism had a significant association with infertility (p < 0.001) and the AA genotype was also highly significantly associated with high sperm DNA damage (p < 0.001).

CONCLUSION

This study demonstrates that the PRM1 c.-190C>A polymorphism is associated with sperm DNA fragmentation, which may impact male infertility in the Turkish population. Further research with larger groups and in various other study populations will be required to clarify the impact of protamine and YBX2 gene polymorphisms on male infertility.

Evaluation of sperm protamine deficiency and apoptosis in infertile men with idiopathic teratozoospermia

Objective

Sperm morphology plays an important role in infertility, especially in cases of defects in the heads of spermatozoa. Tapered-head or elongated-head spermatozoa are examples of morphological abnormalities. The aim of this study was to compare the semen parameters, levels of protamine deficiency, and frequency of apoptosis between patients with normozoospermia and those with teratozoospermia with tapered-head spermatozoa.

Methods

Fifty-two semen samples (27 patients with tapered-head sperm and 25 fertile men) were collected and semen analysis was performed according to the World Health Organization criteria for each sample. Protamine deficiency and the percentage of apoptotic spermatozoa were evaluated using chromomycin A3 (CMA3) staining and terminal deoxynucleotidyl transferase dUTP nick-end labelling (TUNEL) assays, respectively.

Results

Sperm concentration, motility, and normal morphology in the tapered-head spermatozoa (cases) were significantly lower than in the normozoospermic samples (controls). CMA3-reactive spermatozoa (CMA3+) in the case group were more common than in the controls. Apoptotic spermatozoa (TUNEL-positive) were significantly more common in the cases than in the controls.

Conclusion

This analysis showed that tapered-head spermatozoa contained abnormal chromatin packaging and exhibited a high rate of apoptosis, which can be considered to be an important reason for the impaired fertility potential in teratozoospermic patients with tapered-head spermatozoa.

Polymorphisms of protamine genes contribute to male infertility susceptibility in the Chinese Han population

Protamine (PRM) plays important roles in the packaging of DNA within the sperm nucleus. To investigate the role of PRM1/2 and transition protein 1 (TNP1) polymorphisms in male infertility, 636 infertile men and 442 healthy individuals were recruited into this case-controlled study of the Chinese Han population, using MassARRAY technology to analyze genotypes. Our analysis showed that there were no significant differences between controls and infertile cases among the five single nucleotide polymorphisms identified in PRM1, PRM2 and TNP1 [rs737008 (G/A), rs2301365 (C/A), rs2070923 (C/A), rs1646022 (C/G) and rs62180545 (A/G)]. However, we found that the PRM1 and PRM2 haplotypes GCTGC, TCGCA and TCGCC exhibited significant protective effects against male infertility compared to fertile men, while TCGGA, GCTCC and TCGGC represented significant risk factors for spermatogenesis. Our data showed that rs737008 and rs2301365 in PRM1, and rs1646022 in PRM2, were significantly associated with male infertility and that gene–gene interaction played a role in male infertility. A linkage disequilibrium plot for the five SNPs showed that rs737008 was strongly linked with both rs2301365 and rs2070923. These findings are likely to help improve our understanding of the etiology of male infertility. Further studies should include a larger number of genes and SNPs, particularly growing critical genes; such studies will help us to unravel the effect of individual genetic factors upon male infertility.

Viable offspring obtained from Prm1-deficient sperm in mice

Protamines are expressed in the spermatid nucleus and allow denser packaging of DNA compared with histones. Disruption of the coding sequence of one allele of either protamine 1 (Prm1) or Prm2 results in failure to produce offspring, although sperm with disrupted Prm1 or Prm2 alleles are produced. Here, we produced Prm1-deficient female chimeric mice carrying Prm1-deficient oocytes. These mice successfully produced Prm1(+/-) male mice. Healthy Prm1(+/-) offspring were then produced by transferring blastocysts obtained via in vitro fertilization using zona-free oocytes and sperm from Prm1(+/-) mice. This result suggests that sperm lacking Prm1 can generate offspring despite being abnormally shaped and having destabilised DNA, decondensed chromatin and a reduction in mitochondrial membrane potential. Nevertheless, these mice showed little derangement of expression profiles.

Polymorphisms in Protamine 1 and Protamine 2 predict the risk of male infertility: a meta-analysis

Several studies have investigated the association between polymorphisms in protamine 1 and 2 genes and male infertility risk, with inconsistent results to date. This meta-analysis based on the 13 published case-control studies, including 7350 cases and 6167 controls, was performed to further establish the potential association between the 6 common single nucleotide polymorphisms (rs35576928, rs737008, rs35262993, rs2301365, rs1646022, rs2070923) in protamines 1 and 2 and male infertility. The -190C > A (rs2301365) polymorphism was identified as a risk factor for male infertility under all models. Interestingly, rs1646022 and rs737008 polymorphisms exerted protective effects against male sterility in Asian and population-based under some models. No associations between the remaining SNPs and male sterility were observed.

Investigation of the association between the outcomes of sperm chromatin condensation and decondensation tests, and assisted reproduction techniques

The main purpose of this prospective study is to examine possible influences of abnormalities of sperm nuclear condensation and chromatin decondensation with sodium dodecyl sulphate (SDS)-EDTA on outcomes of intrauterine insemination (IUI) or intracytoplasmic sperm injection (ICSI) cycles. Semen samples from 122 IUI and 236 ICSI cycles were evaluated. Before semen preparation for IUI or ICSI, basic semen analysis was performed and a small portion from each sample was spared for fixation. The condensation of sperm nuclear chromatin was evaluated with acidic aniline blue, followed by sperm chromatin decondensation by SDS-EDTA and evaluation under light microscope. Ongoing pregnancy rate was 24% and 26.2% in the IUI and ICSI groups respectively. The chromatin condensation rate was significantly higher in the ongoing pregnancy-positive group compared to the negative group, both in IUI (P = 0.042) and ICSI groups (P = 0.027), and it was positively correlated with ongoing pregnancy rate in both IUI and ICSI groups (P = 0.015, r = 0.214 and P = 0.014, r = 0.312 respectively). Chromatin decondensation rates were not significantly different in neither of the groups. These results indicate that IUI and ICSI outcome is influenced by the rate of spermatozoa with abnormal chromatin condensation. Sperm chromatin condensation with aniline blue is useful for selecting assisted reproduction techniques (ART) patients.

RHOXF2 gene, a new candidate gene for spermatogenesis failure

INTRODUCTION

Genes involved in testicular differentiation, spermatogenesis, proliferation and apoptosis of germ cells have been shown to evolve rapidly and display rapid DNA changes. These genes are therefore good candidates for explaining impairments in spermatogenesis. Initial studies of some of these genes appear to confirm this hypothesis. The RHOXF2 candidate gene belongs to the RHOX family clustered in Xq24 and is specifically expressed in the testis. It contains four exons and codes for a 288 amino acid (aa) transcription factor. It has a high degree of homology (>99.9%) with its paralogue RHOXF2B, which is also preferentially expressed in the testis.

OBJECTIVES

To sequence RHOXF2 and RHOXF2B in intracytoplasmic sperm injection (ICSI) patients and identify any single-nucleotide polymorphisms (SNPs) associated with impaired spermatogenesis.

MATERIALS

A cohort of 327 patients in ICSI programmes at Poissy and Bichat hospitals. All patients gave their written, informed consent to participation. One hundred patients had unaffected spermatogenesis and 227 displayed impaired spermatogenesis.

METHODS

The four exons in each of RHOXF2 and RHOXF2B were sequenced in 47 patients with oligospermia or non-obstructive azoospermia. Given that exons 2 and 3 were found to harbour most of the SNPs, only these two exons were sequenced in the remaining 280 subjects.

RESULTS

Due to the extremely high degree of sequence identity between RHOXF2 and RHOXF2B, we were not able to distinguish between the sequences of these two genes. Although 9 SNPs were identified, there were no significant frequency differences between ICSI patients with normal vs. impaired spermatogenesis. Two insertions were identified: a 21-nucleotide insertion was retrieved in both groups and a guanine insertion (inducing a premature stop codon) only found in two patients with impaired spermatogenesis.

CONCLUSION/OUTLOOK

RHOXF2 is a good candidate for rapid evolution by positive selection. Analysis of the polymorphism frequency in exons 2 and 3 did not allow us to correlate the identified SNPs with male infertility. However, a single nucleotide insertion was identified only in men with impaired spermatogenesis. Further work will be needed to establish whether genetic changes in RHOXF2 can give rise to defects in spermatogenesis.

The Genetics of Infertility: Current Status of the Field

Infertility is a relatively common health condition, affecting nearly 7% of all couples. Clinically, it is a highly heterogeneous pathology with a complex etiology that includes environmental and genetic factors. It has been estimated that nearly 50% of infertility cases are due to genetic defects. Hundreds of studies with animal knockout models convincingly showed infertility to be caused by gene defects, single or multiple. However, despite enormous efforts, progress in translating basic research findings into clinical studies has been challenging. The genetic causes remain unexplained for the vast majority of male or female infertility patients. A particular difficulty is the huge number of candidate genes to be studied; there are more than 2,300 genes expressed in the testis alone, and hundreds of those genes influence reproductive function in humans and could contribute to male infertility. At present, there are only a handful of genes or genetic defects that have been shown to cause, or to be strongly associated with, primary infertility. Yet, with completion of the human genome and progress in personalized medicine, the situation is rapidly changing. Indeed, there are 10-15 new gene tests, on average, being added to the clinical genetic testing list annually.

Protamine-1 and -2 polymorphisms and gene expression in male infertility: an Italian study

BACKGROUND

Correct histone/protamine replacement is an important stage in chromatin condensation during spermiogenesis in humans. There are two types of protamines: protamine 1 (P1) and the protamine 2 family (P2, P3, and P4), coded by the genes PRM1 and PRM2.

AIM

We analyze the sequences and gene expression of PRM1 and PRM2 and their relationship with defective spermatogenesis.

MATERIALS AND METHODS

Sequence analysis was carried out on 163 patients attending our laboratory for analysis of seminal fluid. Patients were divided into three groups: normozoospermic (53), teratozoospermic (60), and azoospermic (50). Gene expression was analyzed in seven patients with azoospermia and one with cryptozoospermia.

RESULTS

Seven single nuclotide polymorphisms (SNP) were identified: G54A, G102T and C230A for PRM1, and C246T, G288C, G298C and C373A for PRM2. For C230A, the CA genotype was present in 38% of teratozoospermic vs 55% of normozoospermic and 64% of azoospermic patients; for C373A, CA was found in 37% of teratozoospermic vs 47% of normozoospermic and 64% of azoospermic patients. In contrast, for G298C, GC was more common in the teratozoospermic (63%) than in the normozoospermic (49%) or azoospermic (48%) groups. These differences could suggest a greater susceptibility of these patients to abnormal sperm morphology. In five patients the levels of transcripts were reduced with respect to the control.

CONCLUSION

These data suggest that premeiotic arrest is associated with extremely reduced protamine expression. New studies of both PRM1 and PRM2 and their mRNA expression could help us better understand the molecular mechanisms underlying the protamine transcription and translation processes.

Single nucleotide polymorphisms in genes that are common targets of luteotropin and luteolysin in primate corpus luteum: computational exploration

Luteal insufficiency affects fertility and hence study of mechanisms that regulate corpus luteum (CL) function is of prime importance to overcome infertility problems. Exploration of human genome sequence has helped to study the frequency of single nucleotide polymorphisms (SNPs). Clinical benefits of screening SNPs in infertility are being recognized well in recent times. Examining SNPs in genes associated with maintenance and regression of CL may help to understand unexplained luteal insufficiency and related infertility. Publicly available microarray gene expression databases reveal the global gene expression patterns in primate CL during the different functional state. We intend to explore computationally the deleterious SNPs of human genes reported to be common targets of luteolysin and luteotropin in primate CL. Different computational algorithms were used to dissect out the functional significance of SNPs in the luteinizing hormone sensitive genes. The results raise the possibility that screening for SNPs might be integrated to evaluate luteal insufficiency associated with human female infertility for future studies.

PRM1 variant rs35576928 (Arg>Ser) is associated with defective spermatogenesis in the Chinese Han population

Protamine genes play important roles in DNA packaging within the sperm nucleus. In order to evaluate the association of PRM1, PRM2, KIT and KITLG variants with susceptibility to severely defective spermatogenesis, 309 male infertility patients (199 cases with non-obstructive azoospermia and 110 cases with severe oligozoospermia) and 377 controls were recruited in the Chinese Han population. This study genotyped 38 single-nucleotide polymorphisms (SNP) in PRM1, PRM2, KIT and KITLG using Sequenom iplex. The results showed that PRM1 variant rs35576928 (p.R34S) was significantly associated with severe oligozoospermia and played a protective role against the disease (P=0.0079, Bonferroni correction, OR 0.426). The dominant model (variant-containing genotypes) of the SNP was confirmed to protect against the occurrence of oligozoospermia (P=0.0078, Bonferroni correction, OR 0.387). Haplotype analysis of PRM1 and PRM2 in combination exhibited that haplotype TACCGGC exhibited a significant protective effect against the occurrence of oligozoospermia when compared with controls (P=0.002, Bonferroni correction, OR 0.602). Haplotype TACCTGC was strongly associated with risk of the clinical phenotype severe oligozoospermia (P=0.002, Bonferroni correction, OR 2.716). The findings indicated that PRM1 variant rs35576928 (p.R34S) was associated with severely defective spermatogenesis in the Chinese Han population. Male spermatogenic failure may be associated with gene variants. We demonstrated whether such genetic variation of PRM1 and PRM2 affected clinicopathological characteristics and conferred susceptibility to this entity. In this study, we found that PRM1 variant rs35576928 (Arg>Ser) played a protective role against severe oligozoospermia. The dominant model analysis (variant-containing genotypes) confirmed that the SNP was a risk factor of a spermatogenesis defect. Haplotype analysis of PRM1 and PRM2 showed that TACCGGC was a common factor protecting against severe oligozoospermia, while the haplotype TACCTGC was strongly associated with the risk of the severe oligozoospmeria. Our findings indicate that the PRM1 variant rs35576928 (Arg>Ser) is associated with spermatogenesis defect in the Chinese Han population.

Functional and Molecular Characterization for the Damp-Obstructed Rat Model in Chinese Medicine

Functional and molecular characterization was performed on the major organs of damp-obstructed rats by applying expression datasets of microarray experiments and real-time RT-PCR. Gene ontology repertoires, i.e. cellular component, molecular function, and biological process were used to classify differentially expressed genes in the major organs of rats upon treatment of dampness. As to the cellular component, over-expression of genes associated with the plasma membrane was observed in the stomach, spleen, kidney, heart, liver, and lung. Genes associated with translational machinery, endoplasmic recticulum membrane, Golgi apparatus, and nuclear envelope were down-regulated in the stomach. Concerning the molecular function, genes associated with oxidoreductase activity were up-regulated in the stomach, spleen, kidney, lung, and brain. Channel activity, membrane receptor, and electron transporter activity were up-regulated in stomach, kidney, and lung. Regarding the biological process, genes associated with signal transduction were up-regulated in the stomach, while genes associated with biosynthesis and ATP metabolism were down-regulated. In the spleen, melanin biosynthesis was up-regulated while hormone-related activities were down-regulated. In the kidney, genes associated with nucleotide biosynthesis and ATP metabolism were depressed. In the heart and liver, apoptosis was up-regulated while immune response and RAS signal transduction were down-regulated. Interestingly, genes associated with oncogenesis were up-regulated in the stomach and kidney. Functional fingerprints indicated that dampness weakened membrane structures, depressed metabolic activity (especially ATP metabolism), damaged matrix proteins, enhanced signal transduction, and revealed a positive association with oncogenesis. To quantify the functional impact at the molecular level, mRNA levels of key genes were determined by real-time RT-PCR. The results indicated that ATP storage in kidney, spleen, and stomach was depleted in damp-obstructed rats. We propose that oxidative stress, membrane integrity, melanin biosynthesis, ion channel activity, and ATP metabolism might be hallmarks for damp-obstructed rats. Our results also suggested dampness as a pathogenic factor in rats which is possibly associated with enhanced liabilities of cancer.

The search for SNPs, CNVs, and epigenetic variants associated with the complex disease of male infertility

Understanding the genetic basis of idiopathic male infertility has long been the focus of many researchers. Numerous recent studies have attempted to identify relevant single nucleotide polymorphisms (SNPs) through medical re-sequencing studies in which candidate genes are sequenced in large numbers of cases and controls in the search for risk or causative polymorphisms. Two major characteristics have limited the utility of the re-sequencing studies. First, reported SNPs have only accounted for a small percentage of idiopathic male infertility. Second, SNPs reported to have an association with male infertility based on gene re-sequencing studies often fail validation in follow-up studies. Recent advances in the tools available for genetic studies have enabled interrogation of the entire genome in search of common, and more recently, rare variants. In this review, we discuss the progress of studies on genetic and epigenetic variants of male infertility as well as future directions that we predict will be the most productive in identifying the genetic basis for male factor infertility based on our current state of knowledge in this field as well as lessons learned about the genetic basis for complex diseases from other disease models.

The use of transgenic mouse models in the study of male infertility

Over the past few decades with the rapid advances in embryo and embryonic stem cell manipulation techniques, transgenic mouse models have emerged as a powerful tool for the study of gene function and complex diseases including male infertility. In this review we give a brief history of the development of tools for the production of transgenic mouse models. This spans the advances from early pronuclear injection to the use of targeted embryonic stem cells to produce gene targeted, conditional, and inducible knockout mouse models. Lastly we provide a few examples to illustrate the utility of mouse models in the study of male infertility.

A common haplotype of protamine 1 and 2 genes is associated with higher sperm counts

Sperm chromatin compaction in the sperm head is achieved when histones are replaced by protamines during spermatogenesis. Haploinsufficiency of the protamine 1 (PRM1) or PRM2 gene causes infertility in mice. However, the published data remain inconclusive about a role of PRM1/2 variants in male infertility and their association with semen parameters. By full sequence analysis, we assessed the frequency of sequence variations in PRM1 and PRM2 in three groups of Caucasian patients with idiopathic teratozoospermia and normal (n = 88) or reduced sperm concentration (n = 83) and in men with a high percentage of normal sperm morphology and normal concentrations (n = 77). Two rare (c.54G>A and c.102G>T) and one common SNP (c.230A>C) were identified in PRM1. In PRM2, some rare heterozygous mutations and the two common intronic SNPs 298G>C and 373C>A were detected. None of the PRM1/2 variants was associated with teratozoospermia or individually with other semen parameters. However, significant linkage disequilibrium was detected between the common SNPs of PRM1 and PRM2 which formed haplotypes. Analysis of the pooled group (n = 248) revealed that homozygous carriers of the common haplotype ACC had a twofold higher sperm concentration and count than men lacking this haplotype, with sperm counts of heterozygotes for ACC being midway between the homozygotes. This markedly decreased sperm output might either be caused by spermatozoa lacking the ACC haplotype not being viable, or subject to negative selection. In addition, a significant deviation from Hardy-Weinberg-Equilibrium of these SNPs might indicate natural selection in favour of the ACC allele which leads to higher sperm output and therefore better fertility. In conclusion, for the first time we describe an association of a common haplotype formed by PRM1 and PRM2 with sperm output in a large group of men.

Two-stage genome-wide association study identifies integrin beta 5 as having potential role in bull fertility

Background

Fertility is one of the most critical factors controlling biological and financial performance of animal production systems and genetic improvement of lines. The objective of this study was to identify molecular defects in the sperm that are responsible for uncompensable fertility in Holstein bulls. We performed a comprehensive genome wide analysis of single nucleotide polymorphisms (SNP) for bull fertility followed by a second-stage replication in additional bulls for a restricted set of markers.

Results

In the Phase I association study, we genotyped the genomic sperm DNA of 10 low-fertility and 10 high-fertility bulls using Bovine SNP Gene Chips containing approximately 10,000 random SNP markers. In these animals, 8,207 markers were found to be polymorphic, 97 of which were significantly associated with fertility (p < 0.01). In the Phase II study, we tested the four most significant SNP from the Phase I study in 101 low-fertility and 100 high-fertility bulls, with two SNPs (rs29024867 and rs41257187) significantly replicated. Rs29024867 corresponds to a nucleotide change of C → G 2,190 bp 3' of the collagen type I alpha 2 gene on chromosome 4, while the rs41257187 (C → T) is in the coding region of integrin beta 5 gene on chromosome 1. The SNP rs41257187 induces a synonymous (Proline → Proline), suggesting disequilibrium with the true causative locus (i), but we found that the incubation of bull spermatozoa with integrin beta 5 antibodies significantly decreased the ability to fertilize oocytes. Our findings suggest that the bovine sperm integrin beta 5 protein plays a role during fertilization and could serve as a positional or functional marker of bull fertility.

Conclusion

We have identified molecular markers associated with bull fertility and established that at least one of the genes harboring such variation has a role in fertility. The findings are important in understanding mechanisms of uncompensatory infertility in bulls, and in other male mammals. The findings set the stage for more hypothesis-driven research aimed at discovering the role of variation in the genome that affect fertility and that can be used to identify molecular mechanisms of development.

Extra-germ cell expression of mouse nuclear receptor subfamily 6, group A, member 1 (NR6A1)

Nuclear receptor subfamily 6, group A, member 1 (NR6A1) is an orphan member of the nuclear receptor superfamily and is required for normal mouse embryonic development. In adult mice, NR6A1 is predominantly expressed in spermatogenic cells and growing oocytes of the gonads and has a role in female reproduction by modulating the transcription of the oocyte-specific genes bone morphogenetic protein 15 (Bmp15) and growth differentiation factor 9 (Gdf9). In our goal to further understand the functional role of NR6A1 during postnatal development, we generated a Nr6a1:beta-galactosidase (LacZ) knockin reporter (Nr6a1(LacZ/+)) mouse line in which the Nr6a1:LacZ fusion gene was expressed and then characterized Nr6a1 expression in these reporter mice by performing LacZ staining. Our RT-PCR analyses showed that Nr6a1 was expressed in a variety of somatic tissues (e.g., oviduct and lung) other than gonads of normal adult mice. In adult Nr6a1(LacZ/+) mice, robust LacZ staining was observed in the gametes of gonads. Strong positive LacZ staining was also observed in the sperm of the epididymis, epithelial cells of the oviduct, and bronchioles within the lung. In adult Nr6a1(LacZ/+) mice, positive LacZ staining was observed in other somatic tissues, including hippocampus, cerebral cortex, cerebellum, and thalamus of brain; pars intermedia and pars anterior of pituitary; parathyroid; and islet of pancreas. NR6A1 expression in sperm within the epididymis, epithelial cells in the oviduct, and bronchioles of the lung was further confirmed by immunohistochemical studies. Nr6a1 is expressed not only in the germ cells of mouse gonads but also in a variety of somatic tissues, including epididymis, oviduct, brain, and pituitary. The extra-germ cell expression of NR6A1 makes it a less attractive contraceptive.

Gene polymorphisms/mutations relevant to abnormal spermatogenesis

Despite the identification of an increasing number of candidate genes involved in spermatogenesis, the armamentarium of diagnostic genetic tests in male infertility remains extremely limited. A number of new causative mutations have been reported for hypogonadotrophic hypogonadism but still the genetic diagnosis in this pathological condition is made only in about 20% of cases. The sole molecular genetic test that is routinely proposed in severe spermatogenic disturbances is screening for Yq microdeletion. The search for causative mutations in the Y chromosome, and in autosomal and X-linked genes, has mostly been unsuccessful. The paucity of gene mutations raises questions about the appropriateness of the currently used screening approaches. Among the proposed genetic risk factors, gr/gr deletion of the Y chromosome seems to be the most promising polymorphism. Other polymorphisms are awaiting further confirmation, whereas for some (POLG, DAZL, USP26, FSHR) a lack of association with abnormal spermatogenesis has now been ascertained. It is likely that some polymorphisms lead to testicular dysfunction only when in association with a specific genetic background or with environmental factors. Future large-scale studies with stringent study design may provide a more efficient way to identify clinically relevant genetic factors of male infertility.

Meichroacidin containing the membrane occupation and recognition nexus motif is essential for spermatozoa morphogenesis

Meichroacidin (MCA) is a highly hydrophilic protein that contains the membrane occupation and recognition nexus motif. MCA is expressed during the stages of spermatogenesis from pachytene spermatocytes to mature sperm development and is localized in the male meiotic metaphase chromosome and sperm flagellum. MCA sequences are highly conserved in Ciona intestinalis, Cyprinus carpio, and mammals. To investigate the physiological role of MCA, we generated MCA-disrupted mutant mice; homozygous MCA mutant males were infertile, but females were not. Sperm was rarely observed in the caput epididymidis of MCA mutant males. However, little to no difference was seen in testis mass between wild-type and mutant mice. During sperm morphogenesis, elongated spermatids had retarded flagellum formation and might increase phagocytosis by Sertoli cells. Immunohistochemical analysis revealed that MCA interacts with proteins located on the outer dense fibers of the flagellum. The testicular sperm of MCA mutant mice was capable of fertilizing eggs successfully via intracytoplasmic sperm injection and generated healthy progeny. Our results suggest that MCA is essential for sperm flagellum formation and the production of functional sperm.

Identification of genetic variation in the 5' and 3' non-coding regions of the protamine genes in patients with protamine deregulation

Deregulation of sperm nuclear protamine ratio (P1/P2) has been shown to correlate with male factor infertility in humans, but the cause of this abnormal protein expression has yet to be identified. Recent studies have shown that there is little genetic variability in the coding regions of either of the protamine gene sequences. However, these studies did not investigate the 5' or 3' non-coding regions of these genes for mutations that might account for changes in the transcriptional or translational regulation of the protamines. In an effort to determine if genetic variation in these non-coding regions may account for aberrant protamine expression, we have sequenced the 5' and 3' untranslated regions (UTRs) of both protamine 1 (P1) and protamine 2 (P2) genes in a population of infertile men with protamine deregulation, men presenting for infertility work-up with normal protamine ratios, and a population of unrelated, fertile men from the Utah Genetic Reference Project (UGRP). This analysis has identified 14 single nucleotide polymorphisms (SNPs), of which 13 were novel SNPs in the UTRs of P1 and P2, and verified the existence of a variable length repeat (VLR), GAn, in the P2 5' region. The SNP frequencies and VLR allelic frequencies did not achieve statistical significance between the populations, however, one of the SNPs identified in the 3' UTR of protamine 2 was found at a low frequency in the abnormal protamine patients, but was completely absent in men with verified normal protamine ratio and donors of known fertility. In conclusion, a number of SNPs have been reported in the protamine genes and the untranslated regions, however, these gene variants do not appear to be responsible for protamine deficiency. Hence, the underlying cause for aberrant protamine expression may possibly be due to abnormalities in candidate spermatogenic transcriptional/translational regulators, post-translational modifiers, or as-of-yet unidentified factors affecting the testicular environment.

The aetiology of sperm protamine abnormalities and their potential impact on the sperm epigenome

During the elongating spermatid stage of spermatogenesis, there is a step-wise replacement of nuclear histones with protamines 1 and 2. In fertile men, the ratio of protamine 1/protamine 2 (P1/P2) is within the narrow range of 0.8-1.2. Ratios above or below that range are associated with infertility, exhibiting a wide range of defects including decreased sperm counts, morphology, fertilization ability, and embryo implantation capacity. In this review, we highlight studies evaluating potential causes of abnormal protamine expression, including the sequencing of genes relevant to protamine expression in both affected patients and controls. While the variants of the protamine genes themselves do not appear to be responsible for most observed defects, variants of the Contrin gene, a transcription factor and translation repressor, appear to be contributory to some cases of abnormal expression. Additionally, we explore the potential effects of abnormal protamine replacement on the epigenome of human sperm. Ongoing studies are evaluating the role of retained histones and DNA methylation in sperm, which may be affected in sperm with aberrant protamine replacement. This important area of epigenetic research has profound clinical implications.

Gene polymorphisms and male infertility--a meta-analysis and literature review

Many genetic polymorphisms have been studied extensively to elucidate their role in the pathophysiology of male infertility. This article presents a review of the literature following a thorough search of PubMed, a compilation of meta-analyses of studies reporting an association with male fertility where the population(s) could be clearly identified as fertile and/or infertile, and a summary of all polymorphisms that have been investigated in single case-control studies to date. The meta-analyses revealed significant associations between polymorphism and male fertility only for AZF gr/gr deletions (OR 1.81, 1.46-2.24 CI, P<0.00001) and MTHFR 677C-->T (OR 1.39, 1.15-2.69 95% CI, P=0.0006) but not for POLG, DAZL, USP26 or FSHR. The influence of CAG repeat length in AR remains open and debated. Genes encoding nuclear proteins (PRM1/2, TNP1/2) and ER1 are possible candidates for further examination, while the role of TAF7L remains unclear. Polymorphisms in 16 other genes have been investigated in single studies, but the results remain doubtful due to often small and heterogeneous cohorts and in the absence of independent replications. The genetic studies performed so far emphasize the complexity of male infertility as a presumably polygenetic trait amended by environmental, lifestyle or occupational factors.

0610009K11Rik, a testis-specific and germ cell nuclear receptor-interacting protein

Using an in silico approach, a putative nuclear receptor-interacting protein 0610009K11Rik was identified in mouse testis. We named this gene testis-specific nuclear receptor-interacting protein-1 (Tnrip-1). Tnrip-1 was predominantly expressed in the testis of adult mouse tissues. Expression of Tnrip-1 in the testis was regulated during postnatal development, with robust expression in 14-day-old or older testes. In situ hybridization analyses showed that Tnrip-1 is highly expressed in pachytene spermatocytes and spermatids. Consistent with its mRNA expression, Tnrip-1 protein was detected in adult mouse testes. Immunohistochemical studies showed that Tnrip-1 is a nuclear protein and mainly expressed in pachytene spermatocytes and round spermatids. Moreover, co-immunoprecipitation analyses showed that endogenous Tnrip-1 protein can interact with germ cell nuclear receptor (GCNF) in adult mouse testes. Our results suggest that Tnrip-1 is a testis-specific and GCNF-interacting protein which may be involved in the modulation of GCNF-mediated gene transcription in spermatogenic cells within the testis.

Genetic risk factors in male infertility

The etiopathogenesis of testicular failure remains unknown in about half of the cases and is referred to as "idiopathic infertility". "Idiopathic" testicular failure is of probable genetic origin since the number of genes involved in human spermatogenesis is likely thousands and only a small proportion of them have been identified and screened in infertile men. In parallel with studies aimed to identify mutations with a clear cause-effect relationship in spermatogenesis candidate genes, there is an increasing interest towards genetic susceptibility factors to male infertility. Despite many efforts, only a few clinically relevant polymorphisms have been identified. This is mainly related to the multifactorial nature of male infertility and to the inappropriate study design of the majority of the studies. The most promising polymorphisms are in genes involved in the endocrine regulation of spermatogenesis and on the Y chromosome, the "gr/gr" deletions. Polymorphisms are generally considered as co-factors. Their final effect on testis function and fertility is probably modulated by the genetic background of each individual and/or by the presence of certain environmental factors. In this review, recent findings concerning some of the most widely studied polymorphisms and male infertility will be discussed.

Mutations in the protamine 1 gene associated with male infertility

In elongating spermatids, human sperm chromatin undergoes a complex compaction in which the transition proteins are extensively replaced by the protamine proteins. Several human studies demonstrate that expression of the protamine proteins is altered in some men with male infertility. For this study, we screened the PRM1 (protamine 1) gene for mutations in a large cohort of 281 men seeking infertility treatment. We identified the c.102G>T transversion that results in an p.Arg34Ser amino acid change in two men. One of these patients presented with oligozoospermia associated with increased sperm DNA fragmentation. The second individual was normospermic but together with his partner sought treatment for idiopathic couple infertility. We also identified a novel missense mutation (c.119G>A, p.Cys40Tyr) in a man with oligoasthenozoospermia. These mutations were not observed in control populations. Interestingly, we also detected variants both 5' and 3' to the PRM1 open-reading frame specifically in infertile individuals. Four individuals with unexplained severe oligozoospermia were heterozygote for a c.-107G>C change that is located at -15 bp from the transcription initiation site of the gene. This mutation may influence PRM1 expression. In addition, a c.*51G>C variant was detected in the 3'UTR of PRM1 specifically in a man with severe oligoasthenozoospermia.