Multiple functional copies of the RBM gene family, a spermatogenesis candidate on the human Y chromosome

Clinical implications of Y chromosome microdeletions among infertile men

Male factor infertility contributes significantly to couples facing difficulty achieving a pregnancy. Genetic factors, and specifically those related to the Y chromosome, may occur in up to 15% of men with oligozoospermia or azoospermia. A subset of loci within the Y chromosome, known as the azoospermia factors (AZFa, AZFb, and AZFc), have been associated with male infertility. Emerging evidence has demonstrated that microdeletions of at least a subset of these regions may also have impacts on systemic conditions. This review provides a brief review of male infertility and the structure of the Y chromosome, and further highlights the role of Y chromosome microdeletions in male infertility and other systemic disease.

The Role of Number of Copies, Structure, Behavior and Copy Number Variations (CNV) of the Y Chromosome in Male Infertility

The World Health Organization (WHO) defines infertility as the inability of a sexually active, non-contracepting couple to achieve spontaneous pregnancy within one year. Statistics show that the two sexes are equally at risk. Several causes may be responsible for male infertility; however, in 30–40% of cases a diagnosis of idiopathic male infertility is made in men with normal urogenital anatomy, no history of familial fertility-related diseases and a normal panel of values as for endocrine, genetic and biochemical markers. Idiopathic male infertility may be the result of gene/environment interactions, genetic and epigenetic abnormalities. Numerical and structural anomalies of the Y chromosome represent a minor yet significant proportion and are the topic discussed in this review. We searched the PubMed database and major search engines for reports about Y-linked male infertility. We present cases of Y-linked male infertility in terms of (i) anomalies of the Y chromosome structure/number; (ii) Y chromosome misbehavior in a normal genetic background; (iii) Y chromosome copy number variations (CNVs). We discuss possible explanations of male infertility caused by mutations, lower or higher number of copies of otherwise wild type, Y-linked sequences. Despite Y chromosome structural anomalies are not a major cause of male infertility, in case of negative results and of normal DNA sequencing of the ascertained genes causing infertility and mapping on this chromosome, we recommend an analysis of the karyotype integrity in all cases of idiopathic fertility impairment, with an emphasis on the structure and number of this chromosome.

Copy number variation of functional RBMY1 is associated with sperm motility: an azoospermia factor-linked candidate for asthenozoospermia

STUDY QUESTION

What is the influence of copy number variation (CNV) in functional RNA binding motif protein Y-linked family 1 (RBMY1) on spermatogenic phenotypes?

SUMMARY ANSWER

The RBMY1 functional copy dosage is positively correlated with sperm motility, and dosage insufficiency is an independent risk factor for asthenozoospermia.

WHAT IS KNOWN ALREADY

RBMY1, a multi-copy gene expressed exclusively in the adult testis, is one of the most important candidates for male infertility in the azoospermia factor (AZF) region of the Y-chromosome. RBMY1 encodes an RNA-binding protein that serves as a pre-mRNA splicing regulator during spermatogenesis, and male mice deficient in Rbmy are sterile.

STUDY DESIGN, SIZE, DURATION

A total of 3127 adult males were recruited from 2009 to 2016; of this group, the dosage of RBMY1 functional copy were investigated in 486 fertile males. In the remaining 2641 males with known spermatogenesis status, 1070 Y-chromosome haplogroup (Y-hg) O3* or O3e carriers without chromosomal aberration or known AZF structure mutations responsible for spermatogenic impairment, including 506 men with normozoospermia and 564 men with oligozoospermia or/and asthenozoospermia, were screened, and the RBMY1 functional copy dosage and copy conversion were determined to explore their associations with sperm phenotypes. The correlation between RBMY1 dosage and its mRNA level or RBMY1 protein level and the correlation between sperm RBMY1 level and motility were analysed in 15 testis tissue samples and eight semen samples. Ten additional semen samples were used to confirm the subcellular localization of RBMY1 in individual sperm.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All the Han volunteers donating whole blood, semen and testis tissue were from southwest China. RBMY1 copy number, copy conversion, mRNA/protein amount and protein location in sperm were detected using the AccuCopy® assay method, paralog ratio test, quantitative PCR, western blotting and immunofluorescence staining methods, respectively.

MAIN RESULTS AND THE ROLE OF CHANCE

This study identified Y-hg-independent CNV of functional RBMY1 in the enrolled population. A difference in the distribution of RBMY1 copy number was observed between the group with normal sperm motility and the group with asthenozoospermia. A positive correlation between the RBMY1 copy dosage and sperm motility was identified, and the males with fewer than six copies of RBMY1 showed an elevated risk for asthenozoospermia relative to those with six RBMY1 copies, the most common dosage in the population. The RBMY1 copy dosage was positively correlated with its mRNA and protein level in the testis. Sperm with high motility were found to carry more RBMY1 protein than those with relatively low motility. The RBMY1 protein was confirmed to predominantly localize in the neck and mid-piece region of sperm as well as the principal piece of the sperm tail. Our population study completes a chain of evidence suggesting that RBMY1 influences the susceptibility of males to asthenozoospermia by modulating sperm motility.

LIMITATIONS REASONS FOR CAUTION

High sequence similarity between the RBMY1 functional copies and a large number of pseudogenes potentially reduces the accuracy of the copy number detection. The mechanism underlying the CNV in RBMY1 is still unclear, and the effect of the structural variations in the RBMY1 copy cluster on the copy dosage of other protein-coding genes located in the region cannot be excluded, which may potentially bias our observations.

WIDER IMPLICATIONS OF THE FINDINGS

Asthenozoospermia is a multi-factor complex disease with a limited number of proven susceptibility genes. This study identified a novel genomic candidate independently contributing to the condition, enriching our understanding of the role of AZF-linked genes in male reproduction. Our finding provides insight into the physiological and pathological characteristics of RBMY1 in terms of sperm motility, supplies persuasive evidence of the significance of RBMY1 copy number analysis in the clinical counselling of male infertility resulting from asthenozoospermia.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the National Natural Science Foundation of China (Nos. 81370748 and 30971598). The authors have no conflicts of interest.

RBMY, a novel inhibitor of glycogen synthase kinase 3β, increases tumor stemness and predicts poor prognosis of hepatocellular carcinoma

Male predominance of hepatocellular carcinoma (HCC) occurs particularly among young children aged 6-9 years, indicative of a possible role of the Y chromosome-encoded oncogene in addition to an androgenic effect. The discovery of oncogenic activation of RBMY (RNA-binding motif on Y chromosome), which is absent in normal hepatocytes but present in male HCC tissues, sheds light on this issue. Herein, we report on a critical hepatocarcinogenic role of RBMY and its ontogenic origin. During liver development, the Ser/Thr phosphorylated RBMY is expressed in the cytoplasm of human and rodent fetal livers. It is then silenced in mature hepatocytes and restricted to scarce expression in the bile ductular cells. Upon hepatocarcinogenesis, a noteworthy increase of cytoplasmic and nuclear RBMY is observed in HCC tissues; however, only the former is expressed dominantly in hepatic cancer stem cells and correlates significantly to a poor prognosis and decreased survival rate in HCC patients. Cytoplasmic expression of RBMY, which is mediated by binding to nuclear exporter chromosome region maintenance 1 and further enriched upon Wnt-3a stimulation, confers upon tumor cells the traits of cancer stem cell by augmenting self-renewal, chemoresistance, cell-cycle progression, proliferation, and xenograft tumor growth. This is achieved mechanistically through increasing Ser9 phosphorylation-inactivation of glycogen synthase kinase 3β by RBMY, thereby impeding the glycogen synthase kinase 3β-dependent degradation of β-catenin and eventually inducing the nuclear entry of β-catenin for the transcription of downstream oncogenes.

CONCLUSION

RBMY is a novel oncofetal protein that plays a key role in attenuating glycogen synthase kinase 3β activity, leading to aberrant activation of Wnt/β-catenin signaling, which facilitates malignant hepatic stemness; because of its absence from normal human tissues except the testis, RBMY represents a feasible therapeutic target for the selective eradication of HCC cells in male patients.

The Y chromosome in the era of intracytoplasmic sperm injection: a personal review

The Y chromosome contains 60 multicopy genes composed of nine different gene families concentrated in regions of multiple repeat sequences called amplicons arranged in mirror images called palindromes. This pattern is susceptible to deletions caused by homologous recombination with itself, and can explain the presence of small numbers of sperm in otherwise azoospermic men.

Use of ethnicity-specific sequence tag site markers for Y chromosome microdeletion studies

INTRODUCTION

Microdeletions in the azoospermia factor region on the long arm of Y chromosome are associated with spermatogenic failure. There are many markers for the diagnosis of Y chromosome microdeletion analysis, but in routine practice only a limited set of markers can be tested.

OBJECTIVE

The objectives of this study were to determine the frequency of Y chromosome microdeletion in idiopathic cases of male infertility in India, to attempt genotype-phenotype correlation, and to evaluate whether markers to be tested for diagnosis of Y chromosome microdeletion should be ethnicity specific.

METHODS

Microdeletions in the Y chromosome were analyzed in 200 infertile males. The six sequence tag site (STS) markers prescribed by the European Academy of Andrology (EAA) were used initially. Patients in whom no deletions were detected by use of these markers were tested by markers selected from other studies from India.

RESULTS

The STS markers prescribed by EAA detected deletions in only 6 (3%) of 200 infertile males. However, markers selected from previous Indian studies showed deletions in an additional 15 (7.5%) of infertile males. Overall, Y chromosome microdeletions were observed in 21 (10.5%) of 200 patients. Of these, 13 were cases of azoospermia and 8 were cases of severe oligospermia.

CONCLUSION

The markers prescribed by EAA alone are not suitable for the diagnosis of Y chromosome microdeletions in infertile males. The protocol for identification of Y chromosome microdeletions in cases of nonobstructive azoospermia/severe oligospermia would have to include a different set of STS markers.

Y Chromosome microdeletion and altered sperm quality in human males with high concentration of seminal hexachlorocyclohexane (HCH)

Recent studies have shown Y chromosome microdeletions associated with male infertility. The factors responsible for Y chromosome microdeletions in spermatozoa remain unresolved. However, the environmental pollutants are known to damage DNA in differentiating and maturing germ cells in the male reproductive tract. Therefore, the aim of this study was to investigate the effects of seminal hexachlorocyclohexane (HCH) and its isomers, an environmental pollutant, in 50 fertile and 50 infertile males in relation to semen quality and the incidence of Y chromosome microdeletion in azoospermic factor (AZF) region. As compared to control, an increased HCH level and significantly decreased semen quality were observed in the infertile males. A positive significant association was found between sperm count with alpha-HCH and beta-HCH in the infertile males. A negative significant association was observed between sperm counts with gamma-HCH in asthenospermia patients and with beta-HCH and total HCH in oligo-asthenospermic patients. Out of 100 males studied, we found 10 patients with Yq deletion in AZFa and AZFc regions. Subdivision of infertile group revealed a deletion incidence of 61.5% in azoospermic patients, 11.1% in oligospermic patients and 16.6% in oligo-asthenospermic patients. The presence of Yq deletion in azoospermic patients with a significant mean difference of beta-HCH and total HCH in relation to reduced semen quality seem to corroborate with the mutagenic activity of HCH. The results of this study indicated the susceptibility of male germ line to mutagenic potential of HCH which is an acknowledged risk factor leading to spermatogenic failure.

Genetic dissection of the AZF regions of the human Y chromosome: thriller or filler for male (in)fertility?

The azoospermia factor (AZF) regions consist of three genetic domains in the long arm of the human Y chromosome referred to as AZFa, AZFb and AZFc. These are of importance for male fertility since they are home to genes required for spermatogenesis. In this paper a comprehensive analysis of AZF structure and gene content will be undertaken. Particular care will be given to the molecular mechanisms underlying the spermatogenic impairment phenotypes associated to AZF deletions. Analysis of the 14 different AZF genes or gene families argues for the existence of functional asymmetries between the determinants; while some are prominent players in spermatogenesis, others seem to modulate more subtly the program. In this regard, evidence supporting the notion that DDX3Y, KDM5D, RBMY1A1, DAZ, and CDY represent key AZF spermatogenic determinants will be discussed.

TSPY gene copy number as a potential new risk factor for male infertility

The human TSPY (testis-specific protein, Y-linked) gene family (30-60 copies) is situated in the MSY (male-specific) region of the Y chromosome. Testis-specific expression indicates that the gene plays a role in spermatogenesis. Refined quantitative fluorescence PCR (polymerase chain reaction) was applied to evaluate the relative number of TSPY copies compared with AMELY/X (amelogenin gene, Y-linked) genes in 84 stratified infertile men and in 40 controls. A significantly higher number of TSPY copies was found in infertile men compared with the controls (P = 0.002). The diagnostic discrimination potential of the relative number of TSPY copies was evaluated by receiver operating characteristic curve analysis. TSPY/AMELY was unambiguously found to be powerful in the diagnostic separation of both the control samples and the infertile men, reaching a good level of specificity (0.642) and sensitivity (0.732) at a cut-off point of 0.46. The findings were supported by independently repeated studies of randomly selected positive samples and controls. Evaluation of the TSPY copy number offers a completely new diagnostic approach in relation to the genetic cause of male infertility. The possible effect of the copy number of TSPY genes on spermatogenesis may explain indiscrete pathological alterations of spermatid quality and quantity.

Human Y-chromosome variation and male dysfunction

The Y-chromosome is responsible for sex determination in mammals, which is triggered by the expression of the SRY gene, a testis-determining factor. This particular gene, as well as other genes related to male fertility, are located in the non-recombining portion of the Y (NRY), a specific region that encompasses 95% of the human Y-chromosome. The other 5% is composed of the pseudo-autosomal regions (PARs) at the tips of Yp and Yq, a X-chromosome homologous region used during male meiosis for the correct pairing of sexual chromosomes. Despite of the large size of the human NRY (about 60 Mb), only a few active genes are found in this region, most of which are related to fertility. Recently, several male fertility dysfunctions were associated to microdeletions by STS mapping. Now that the complete genetic map of the human Y-chromosome is available, the role of particular NRY genes in fertility dysfunctions is being investigated. Besides, along with the description of several nucleotide and structural variations in the Y-chromosome, the association between phenotype and genotype is being addressed more precisely. Particularly, several research groups are investigating the association between Y-chromosome types and susceptibility to certain male dysfunctions in different population backgrounds. New insights on the role of the Y-chromosome and maleness are being envisaged by this approach.

The genetic and cytogenetic basis of male infertility

Despite the difficulties in determining the relative maternal vs. paternal contributions to infertility it is often suggested that a male factor problem is implicated in 50% of cases. This review is concerned specifically with male fertility disorders that have a clearly defined genetic component. The genetic causes of infertility can be broken down into Y chromosome deletions (specifically deletions in the AZF a, b, and c regions), single gene disorders (particularly those relating to the CFTR gene), multifactorial causes and chromosome abnormalities. Chromosome abnormalities can be numerical (such as trisomy--full blown or mosaic) or structural (such as inversions or translocations). Of especial interest at present is the incidence of levels of numerical chromosome abnormalities in the sperm of infertile men; prospects for screening sperm for such abnormalities are discussed.

RNA binding motif (RBM) proteins: a novel family of apoptosis modulators?

RBM5 is a known modulator of apoptosis, an RNA binding protein, and a putative tumor suppressor. Originally identified as LUCA-15, and subsequently as H37, it was designated "RBM" (for RNA Binding Motif) due to the presence of two RRM (RNA Recognition Motif) domains within the protein coding sequence. Recently, a number of proteins have been attributed with this same RBM designation, based on the presence of one or more RRM consensus sequences. One such protein, RBM3, was also recently found to have apoptotic modulatory capabilities. The high sequence homology at the amino acid level between RBM5, RBM6, and particularly, RBM10 suggests that they, too, may play an important role in regulating apoptosis. It is the intent of this article to ammalgamate the data on the ten originally identified RBM proteins in order to question the existence of a novel family of RNA binding apoptosis regulators.

Comparison of two methods of in vivo gene transfer by electroporation

OBJECTIVE

To evaluate two contrasting methods of in vivo gene transfer into testicular cells using electroporation, with regard to efficiency of transfer and damage to the testes.

DESIGN

Controlled animal study.

SETTING

Research laboratory at a university medical school.

ANIMAL(S)

8-10-week-old male mice.

INTERVENTION(S)

The reporter construct pCAGGS-LacZ consisting of a cytomegalovirus enhancer/chicken beta-actin promoter attached to the LacZ gene was introduced into the testes in vivo using electroporation. For eight weeks, the efficiency and extent of LacZ gene expression, and the extent to which the testis was damaged by the technique, were investigated.

MAIN OUTCOME MEASURE(S)

Beta-galactosidase activity resulting from expression of the LacZ transgene was verified by X-gal staining, and LacZ mRNA expression was determined by RT-PCR analysis. Potential disorders associated with seminiferous tubular sperm formation were evaluated using the Johnsen score.

RESULT(S)

Long-lasting beta-galactosidase activity was detected in spermatogenic cells up to eight weeks postelectroporation. Apparent damage to spermatogenesis was evident but was transient in nature and recovered with time; this plasticity was particularly evident following rete testes injection.

CONCLUSION(S)

Injection into the rete testis appears to be more suitable for in vivo gene transfer by electroporation than direct intratesticular injection.

Idiopathic cases of male infertility from a region in India show low incidence of Y-chromosome microdeletion

Chromosomal and Y-chromosomal microdeletion analysis has been done in cases of idiopathic infertility with the objective of evaluating the frequency of chromosomal and molecular anomaly as the causal factor of infertility. Barring a few cases of Klinefelter syndrome (XXY or XY/XXY mosaics), no chromosomal anomaly was encountered. Y-microdeletion was analysed by PCR-screening of STSs from different regions of the AZF (AZFa, AZFb, AZFc) on the long arm of the Y, as well as by using DNA probes of the genes RBM, DAZ (Yq), DAZLA (an autosomal homologue of DAZ) and SRY (Yp; sex determining gene). Out of 177 cases examined, 9 (azoospermia - 8 and oligoasthenospermia - 1) showed partial deletion of AZF. The size of deletion varied among patients but AZFc was either totally or partially removed in all of them. In contrast, no deletion was detected in AZFa. Testis biopsy done on a limited number of cases (50) showed diverse stages of spermatogenic arrest with no specific correlation with the genotype. The frequency of Y-chromosome microdeletion in our samples (approximately 5%) is much lower than the frequency (approximately 10%) reported globally and the two previous reports from India. We contend that the frequency may be affected by population structures in different geographical regions.

RBMY, a male germ cell-specific RNA-binding protein, activated in human liver cancers and transforms rodent fibroblasts

The RNA-binding motif (RRM) gene on Y chromosome (RBMY), encoding a male germ cell-specific RNA-binding protein associated with spermatogenesis, was found inserted by hepatitis B virus (HBV) DNA in one childhood hepatocellular carcinoma (HCC). This study is aimed to explore the oncogenic potential of the RBMY protein. The RBMY transcripts, expressed exclusively in the testis of normal people, were detected by reverse transcription-polymerase chain reaction in 36% of HCCs from 90 males and in 67% of hepatoblastoma from six boys. The nontumor liver counter parts, cirrhotic liver tissues from children with biliary atresia, and other types of cancers, such as bile duct, colon, stomach, lung, prostate, and kidney, were all negative for RBMY expression. One to four types of RBMY transcripts, including wild type and variants with N-terminal RRM deletion, C-terminal SRGY (serine-arginine-glycine-tyrosine) boxes deletion, or deletion of both domains, were found in the testis and liver cancer tissues. The wild-type RBMY protein was expressed in the nucleus and demonstrated its tumorigenicity by transformation of mouse fibroblast NIH3T3 cells and in vivo tumor formation. The RBMY variant protein with deletion of C-terminal exons 9-12 was trapped in the cytoplasm and showed decreased tumorigenicity. Our results suggest that RBMY is a new candidate oncogene specific for male liver cancer.

The human spermatozoon--not waving but drowning

The poor quality of the human ejaculate sets man apart from all other mammalian species. Even in normal fertile men the ejaculate may contain up to 85% abnormal forms according to the World Heath Organization (1999). In the wake of this poor semen quality comes extremely poor fertility (Hull et al, 1985) and the highest rates of aneuploidy, pregnancy loss and birth defects in viviparous vertebrates. Thus, the poor quality of human spermatozoa is reflected in both their capacity for fertilization and their genetic integrity. The ultimate cause of defective sperm function is unknown. In certain patients a genetic basis for male infertility has been identified involving DNA deletions on the long arm of the Y chromosome. Such deletions might explain the impoverished semen quality seen in about 10-14% of men with severely impaired spermatogenesis, but fail to explain the infertility seen in most (>85%) cases of male infertility. One of the key attributes and probable causes of defective sperm function is oxidative stress created by excessive ROS generation by the spermatozoa and/or the disruption of antioxidant defence systems in the male reproductive tract. Excess free radical generation frequently involves an error in spermiogenesis resulting in the release of spermatozoa from the germinal epithelium exhibiting abnormally high levels of cytoplasmic retention. The excess cytoplasm contains enzymes that fuel the generation of ROS by the spermatozoa's plasma membrane redox systems. The consequences of such oxidative stress include a loss of motility and fertilizing potential and the induction of DNA damage in the sperm nucleus. The loss of sperm function is due to the peroxidation of unsaturated fatty acids in the sperm plasma membrane as a consequence of which the latter loses its fluidity and the cells lose their function. The causes and consequences of oxidative damage to the DNA in the sperm nucleus are still not known with certainty. The available evidence suggests that early pregnancy loss and morbidity in the offspring, including childhood cancer, are associated with such damage. Developing animal models with which to establish the validity of these relationships and identifying the environmental factors associated with the proposed 'testicular dysgenesis syndrome' will clearly be important tasks for the future.

Y chromosome deletions in azoospermic men in India

Genetic factors cause about 10% of male infertility. Azoospermia factors (AZFa, AZFb, AZFc) are considered to be the most important for spermatogenesis. We therefore made an attempt to evaluate the genetic cause of azoospermia, Y chromosome deletion in particular, in Indian men. We have analyzed a total of 570 men, including 340 azoospermic men and 230 normal control subjects. DNA samples were initially screened with 30 sequence-tagged site (STS) markers representing AZF regions (AZFa, AZFb, AZFc). Samples, with deletion in the above regions were mapped by STS walking. Further, the deletions were confirmed by Southern hybridization using the probes from both euchromatic and heterochromatic regions. Of the total 340 azoospermic men analyzed, 29 individuals (8.5%) showed Y chromosome deletion, of which deletion in AZFc region was the most common (82.8%) followed by AZFb (55.2%) and AZFa (24.1%). Microdeletions were observed in AZFa, whereas macrodeletions were observed in AZFb and AZFc regions. Deletion of heterochromatic and azoospermic regions was detected in 20.7% of the azoospermic men. In 7 azoospermic men, deletion was found in more than 8.0 Mb spanning AZFb and AZFc regions. Sequence analysis at the break points on the Y chromosome revealed the presence of L1, ERV, and other retroviral repeat elements. We also identified a approximately 240-kb region consisting of 125 bp tandem repeats predominantly comprised of ERV elements in the AZFb region. Histological study of the testicular tissue of the azoospermic men, who showed Y chromosome deletion, revealed complete absence of germ cells and presence of only Sertoli cells.

Molecular biology of male infertility

About 15% of couples have reduced fertility and in approximately one-half of all cases the reason is male infertility, usually of genetic origin. Thus, in the context of research in genes involved in reproduction and sex determination, genetic anomalies in gametogenesis are being extensively studied. The most frequent pathogenic causes of male infertility are Y-chromosomal microdeletions (8-15%) in the long arm of the Y chromosome, which, by loss of specific DNA segments, leads to loss of vital genes for sperm production. Infertile men, who attend infertility clinics, rise to 15% among those with azoospermia or spermatogenesis problem. The new technique of intracytoplasmic sperm injection has allowed many infertile men to achieve their dreams of fatherhood. However, the spermatogenic defect is genetic anomalies, which might be a potential risk of transmitting this defect to future offspring. Therefore, genetic counseling of all couples with the diagnosis of male infertility is recommended before their enrolment in intrauterine insemination, in vitro fertilization, and intracytoplasmic sperm injection. The important role of genetic abnormalities in the causation of human male infertility is increasingly recognized. While much remains to be learned in this fast-moving field, considerable progress has been made in the clinical delineation of genetic forms of male infertility and in the characterization of the responsible genes and their mutations or deletions. This review should provide insight into the understanding of parthenogenesis of male infertility in the human.

Characterization of integration patterns and flanking cellular sequences of hepatitis B virus in childhood hepatocellular carcinomas

Hepatitis B virus (HBV) DNA integration into host chromosomes is detected in more than 80% of HBV-related hepatocellular carcinomas (HCC), yet its significance in tumor development remains obscure. In this study, we re-examined the integration pattern of HBV in childhood HCC tissues, which has less environmental confounding factors than adult HCC. The HBV junctions and flanking cellular sequences were amplified from five childhood HCC patients by the inverse polymerase chain reaction (IPCR) method using primers located near HBV direct repeats (DR) 1 and 2. The viral junctions in nine of the ten obtained IPCR clones were demonstrated to be located near HBV DR1, and their patterns were classified to type I integrants. Southern blot analyses demonstrate that the cellular junctions derived from two of the five HCC tissues were male specific and contained sequences homologous to human long interspersed DNA elements (LINE-1). HBV integrant of one HCC tissue (1217T) was integrated into a RNA binding motif Y chromosome (RBMY) gene. The expression of RBMY, which is normally found only in male germ cells, was detected in HCC tissue 1217T by RT-PCR but not in the corresponding non-tumor liver tissue. The prevalence of RBMY expression in liver tissues from the tumor and non-tumor parts of ten other HCC children and seven biliary atresia (BA) children was studied by RT-PCR. No RBMY transcripts were detected in the non-tumor parts of HCC patients or the cirrhotic livers of BA children, whereas 30% (three of ten) of HCC tissues specifically expressed RBMY. The results indicate that HBV integration and activation of RBMY gene expression in liver cells may be associated with the development of childhood HCC.

Y chromosome genes and male infertility

Normal spermatogenesis is a complex process that depends on many factors. Genetics plays a major role in many of these factors including providing a normal hormonal milieu, the development of the testis and ductal system, and control of the stepwise maturation of sperm in the testis. The Y chromosome plays a key role in testis determination and control of spermatogenesis. Understanding how these genes work together can elucidate of the exact cause of infertility in some patients once thought to have idiopathic infertility. It is not only important that patients understand the cause of their infertility. Using sperm from these men to attain pregnancies by assisted reproductive techniques will probably result in infertile male offspring. Additional consequences are currently unknown but are the topic of research investigations.

A comparative study of Y chromosome microdeletions in infertile males from two Chinese populations

PURPOSE

To compare the prevalence and type of Y-microdeletions in Hong Kong and Shanghai men with severe male-factor infertility.

METHODS

Seven Y-linked sequence tagged site (STS) primers and seven gene-specific primers were screened in 293 infertile males (139 from Hong Kong and 154 from Shanghai) and 161 fertile men (61 from Hong Kong and 100 from Shanghai). Serum FSH, LH, and testosterone levels were also measured in these men.

RESULTS

The incidence of Yq microdeletions in nonobstructive azoospermic men from Hong Kong (8.5%) and Shanghai (6%) was similar. Yq microdeletions were observed in severe oligospermic patients (8.5%) from Hong Kong but not from Shanghai. Among the 9 Hong Kong men with Y-microdeletions, 8 had AZFc deletion and one had AZFb deletion. In contrast, 6 of 9 men from Shanghai with Y-microdeletions had AZFb deletion. The incidence of AZFb deletion among Y-microdeleted men was statistically different between the two populations. Two of the men with AZFb deletion also had AZFa and AZFc deletions.

CONCLUSIONS

Regional variations in the type of Y-microdeletion existed between Hong Kong and Shanghai infertile males.

Spontaneous transmission from a father to his son of a Y chromosome microdeletion involving the deleted in azoospermia (DAZ) gene

Microdeletions of the so-called azoospermia factor (AZF) locus of the Y chromosome long arm (Yq) have been recognized as an etiological factor of severe oligozoospermia or azoospermia. Because of this, patients affected are generally infertile unless assisted reproductive techniques are used. We report the case of an oligozoospermic patient (proband) who inherited an extensive Yq microdeletion from his father through a spontaneous pregnancy. Leukocyte DNA was extracted using a commercially available kit. A total of 22 pairs of sequence-tagged site (STSs) based primers, spanning the entire AZF region, were used for the screening. Both the proband and his father carried a Yq microdeletion of the most distal AZF subregion (AZFc) where the deleted in azoospermia (DAZ) gene is located. The proband's father was a sixty-nine-yr-old man who had 3 other children, 2 females and 1 male. This case adds further evidence that the deletion of the DAZ gene is associated with different phenotypic expressions, including normal fertility.

Male infertility, genetic analysis of the DAZ genes on the human Y chromosome and genetic analysis of DNA repair

Many genes that are required for fertility have been identified in model organisms (). Mutations in these genes cause infertility due to defects in development of the germ cell lineage, but the organism is otherwise healthy. Although human reproduction is undoubtedly as complex as that of other organisms, very few fertility loci have been mapped (). This is in spite of the prevalence of human infertility, the lack of effective treatments to remedy germ cell defects, and the cost to couples and society of assisted reproductive techniques. Fifteen percent of couples are infertile and half of all cases can be traced to the male partner. Aside from defects in sperm production, most infertile men are otherwise healthy. This review is divided into two distinct parts to discuss work that: (i) led to the identification of several genes on the Y chromosome that likely function in sperm production; and (ii) implicates DNA repair in male infertility via increased frequency of mutations in DNA from men with meiotic arrest.

Molecular insights into the causes of male infertility

Infertility is a reproductive health problem that affects many couples in the human population. About 13-18% of couple suffers from it and approximately one-half of all cases can be traced to either partner. Regardless of whether it is primary or secondary infertility, affected couples suffer from enormous emotional and psychological trauma and it can constitute a major life crisis in the social context. Many cases of idiopathic infertility have a genetic or molecular basis. The knowledge of the molecular genetics of male infertility is developing rapidly, new "spermatogenic genes" are being discovered and molecular diagnostic approaches (DNA chips) established. This will immensely help diagnostic and therapeutic approaches to alleviate human infertility. The present review provides an overview of the causes of human infertility, particularly the molecular basis of male infertility and its implications for clinical practice.

Specific localization of RBM1a in the nuclei of all cell types except elongated spermatids within seminiferous tubules of the human

Recent studies have indicated that at least three regions (AZF a-c) on the long arm of the Y-chromosome code for factors are involved in spermatogenesis. One of the candidate genes in the AZFb region is RBM1a, coding for a protein with an RNA binding motif. In this study, poly clonal antibodies raised against a 15 amino acid peptide, corresponding to residues 263-304 of the deduced amino acid sequence of RBM1a, has been used to localize the RBM1a protein in the human testis. Immunohistochemistry on normal human testis using this RBM1a antibody, localized the antigen to the nuclei of spermatogonia, primary spermatocytes, and round spermatids but not to the nuclei of elongated spermatids. The antibody also specifically identified the nuclei of Sertoli cells, although the fluorescence was not as strong as in the germ cell nuclei it identified. No specific fluorescence was seen in the nuclei of either peritubular, endothelial or Leydig cells. Western blot of normal human testicular tissue using the anti-RBM1a antibody gave rise to a single specific band of approximately 55 kDa, corresponding to the expected size of RBM1a. In view of its expression in germ cells, and because RBM1a has an RNA binding domain, RBM1a may be involved in RNA processing, such as RNA splicing or RNA export which are events necessary for normal spermatogenesis.

TTY2: a multicopy Y-linked gene family

Genes involved in human male sex determination and spermatogenesis are likely to be located on the Y chromosome. In an effort to identify Y-linked, testis-expressed genes, a cDNA selection library was generated by selecting testis cDNA with Y-cosmid clones. Resultant clones containing repetitive or vector material were eliminated, and 79 of the remaining clones were sequenced. Nineteen cDNAs showed homology with the TTY2 gene, and indicated that TTY2 is part of a large gene family. Screening of a panel of Y-linked cosmids revealed that the TTY2 gene family includes at least 26 members organized in 14 subfamilies. Further investigation revealed that TTY2 genes are arranged in tandemly arrayed clusters on both arms of the Y chromosome, and each gene comprises a series of tandemly arranged repeats. RT-PCR studies for two of these genes revealed that they are expressed in adult and fetal testis, as well as in the adult kidney. None of the genes investigated in detail contain an open reading frame. We conclude that the TTY2 gene family is composed of multiple copies, some of which may function as noncoding RNA transcripts and some may be pseudogenes.

Y chromosome microdeletions and alterations of spermatogenesis

Three different spermatogenesis loci have been mapped on the Y chromosome and named "azoospermia factors" (AZFa, b, and c). Deletions in these regions remove one or more of the candidate genes (DAZ, RBMY, USP9Y, and DBY) and cause severe testiculopathy leading to male infertility. We have reviewed the literature and the most recent advances in Y chromosome mapping, focusing our attention on the correlation between Y chromosome microdeletions and alterations of spermatogenesis. More than 4,800 infertile patients were screened for Y microdeletions and published. Such deletions determine azoospermia more frequently than severe oligozoospermia and involve especially the AZFc region including the DAZ gene family. Overall, the prevalence of Y chromosome microdeletions is 4% in oligozoospermic patients, 14% in idiopathic severely oligozoospermic men, 11% in azoospermic men, and 18% in idiopathic azoospermic subjects. Patient selection criteria appear to substantially influence the prevalence of microdeletions. No clear correlation exists between the size and localization of the deletions and the testicular phenotype. However, it is clear that larger deletions are associated with the most severe testicular damage. Patients with Y chromosome deletions frequently have sperm either in the ejaculate or within the testis and are therefore suitable candidates for assisted reproduction techniques. This possibility raises a number of medical and ethical concerns, since the use of spermatozoa carrying Y chromosome deletions may produce pregnancies, but in such cases the genetic anomaly will invariably be passed on to male offspring.

RBMY genes and AZFb deletions

Microdeletions of the AZFb region of the human Y chromosome usually result in severe consequences for spermatogenesis. AZFb contains at least four kinds of genes/gene families. These include a number of RBMY genes, which are clustered in the AZFb deletion interval. They are amongst the oldest genes on the mammalian Y chromosome, and are related to the gene encoding hnRNPG (RBMX) on the X chromosome. A retroposon-derived version of these genes is found on chromosome 11 that might replace the function of these genes during meiosis, during which time the X and Y chromosomes are transcriptionally inactivated. Each of these genes encodes proteins with an RNA binding motif, and interacts with more ubiquitously expressed proteins involved in pre-mRNA splice site selection. These findings imply that important pre-mRNA processing pathways might be disrupted in the germ cells of AZFb men.

The role of human and mouse Y chromosome genes in male infertility

It was suggested by Ronald Fisher in 1931 that genes involved in benefit to the male (including spermatogenesis genes) would accumulate on the Y chromosome. The analysis of mouse Y chromosome deletions and the discovery of microdeletions of the human Y chromosome associated with diverse defective spermatogenic phenotypes has revealed the presence of intervals containing one or more genes controlling male germ cell differentiation. These intervals have been mapped, cloned and examined in detail for functional genes. This review discusses the genes mapping to critical spermatogenesis intervals and the evidence indicating which are the most likely candidates underlying Y-linked male infertility.

New concepts in operative andrology: a review

Several recently published, or about to be published, controversial issues in operative andrology are clarified and reviewed in this paper. The microsurgical technique for sperm retrieval for nonobstructive azoospermia, the round spermatid controversy and the varicocoele dilemma (why does everybody keep doing varicocoelectomy for male factor infertility?) are presented with salient points that have recently been presented elsewhere and referenced. Finally, at the end, we review briefly what is known about the likelihood of genetic transmission of infertility from male factor patients to their offspring as a result of the new ICSI technology.

Identification of two novel proteins that interact with germ-cell-specific RNA-binding proteins DAZ and DAZL1

The human DAZ (deleted in azoospermia) gene family on the Y chromosome and an autosomal DAZ-like gene, DAZL1, encode RNA-binding proteins that are expressed exclusively in germ cells. Their role in spermatogenesis is supported by their homology with a Drosophila male infertility gene boule and sterility of Daz11 knock-out mice. While all mammals contain a DAZL1 homologue on their autosomes, DAZ homologues are present only on the Y chromosomes of great apes and Old World monkeys. The DAZ and DAZL1 proteins differ in the copy numbers of a DAZ repeat and the C-terminal sequences. We studied the interaction of DAZ and DAZL1 with other proteins as an approach to investigate functional similarity between these two proteins. Using DAZ as bait in a yeast two-hybrid system, we isolated two DAZAP (DAZ-associated protein) genes. DAZAP1 encodes a novel RNA-binding protein that is expressed most abundantly in the testis, and DAZAP2 encodes a ubiquitously expressed protein with no recognizable functional motif. DAZAP1 and DAZAP2 bind similarly to both DAZ and DAZL1 through the DAZ repeats. The DAZAP genes were mapped to chromosomal regions 19p13.3 and 2q33-q34, respectively, where no genetic diseases affecting spermatogenesis are known to map.

Y chromosome microdeletions in cryptorchidism and idiopathic infertility

To clarify whether cryptorchidism might be the expression of an intrinsic congenital testicular abnormality, we investigated the frequency of Y chromosome long arm (Yq) microdeletions in unilateral excryptorchid subjects manifesting an important bilateral testiculopathy. Microdeletion analysis of Yq was performed by polymerase chain reaction in the following subjects: 40 unilateral excryptorchid patients with azoospermia or severe oligozoospermia due to a bilateral severe testiculopathy (Sertoli cell-only syndrome or severe hypospermatogenesis); 20 unilateral excryptorchid men with moderate oligozoospermia and a normal testicular cytological picture in the contralateral testis; 110 patients affected by idiopathic severe primary testiculopathies; 20 patients affected by idiopathic moderate testiculopathy; and, as controls, 50 patients affected by known causes of testiculopathy and 100 fertile men. Eleven of 40 (27.5%) unilateral excryptorchid patients affected by bilateral testiculopathy and 28 of 110 (25.4%) patients affected by idiopathic severe primary testiculopathy showed Yq microdeletions, whereas no microdeletions were found in all the other subjects, nor in male relatives of patients with deletions. Microdeletions were located in different parts of Yq, including known regions involved in spermatogenesis (DAZ and RBM, AZFa, b, and c) and other loci still poorly defined. No difference in localization of deletions was evident between cryptorchid and idiopathic patients. Microdeletions in Yq may be responsible for severe bilateral testicular damage that could be phenotypically expressed by unilateral cryptorchidism, as well as by idiopathic infertility.

Absence of testicular DAZ gene expression in idiopathic severe testiculopathies

Deletions of the DAZ (deleted in azoospermia) gene family are frequently responsible for male infertility and are generally assessed by analyses of genomic DNA extracted from peripheral leukocytes. The multicopy nature of this gene prevents the distinction of intragenic deletions or deletions not involving the whole DAZ gene cluster. Thus it is still unclear whether each DAZ copy is effectively expressed in the testis. We analysed, by reverse transcription-polymerase chain reaction (RT-PCR), the expression of DAZ, RBM and SRY genes, in testicular cells from infertile men affected by idiopathic severe hypospermatogenesis, obstructive azoospermia and Sertoli cell-only syndrome. Normal mRNA for DAZ, RBM and SRY were observed in obstructive azoospermia, whereas only SRY transcripts were detected when only Sertoli cells were present. Nine out of 10 patients affected by idiopathic severe hypospermatogenesis had normal expression of SRY, RBM and DAZ, while in one patient no DAZ transcript was detected, suggesting that his testiculopathy was related to the absence of DAZ expression. The lack of DAZ mRNA in testicular cells with an apparently normal DAZ gene constitution on DNA extracted from leukocytes may be explained by different hypotheses: (i) not all the copies of the DAZ gene cluster are transcribed in the germ cells and the reported patient had a small deletion involving only the active ones; (ii) the patient may be mosaic for the DAZ gene having a normal constitution in leukocytes and be deleted for DAZ gene in the testis; (iii) abnormalities of DAZ transcription may exist. These findings highlight the intrinsic interpretative difficulties of normal PCR analysis for DAZ and RBM on leukocytes and suggest caution in the use of germ cells for assisted reproductive techniques in these cases to avoid transmission of genetic abnormalities to male offspring.

Microdeletions within the azoospermia factor subregions of the Y chromosome in patients with idiopathic azoospermia

OBJECTIVE

To examine the patterns of submicroscopic DNA deletions in the AZF (AZoospermia Factor) subregions of the Y chromosome in patients with idiopathic azoospermia.

DESIGN

Controlled clinical study.

SETTING

University-based infertility clinic.

PATIENT(S)

Infertile men (n = 40) with nonobstructive, idiopathic azoospermia. The control group consisted of proven fathers (n = 14) and healthy women (n = 4).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Semen analysis; polymerase chain reaction amplification of the 37 loci spanning the AZFa, AZFb, and AZFc subregions of the Y chromosome; serum FSH, LH, and testosterone levels; and testicular histologic analysis.

RESULT(S)

Testicular histologic analysis of the subjects revealed Sertoli cell-only syndrome (n = 36) and spermatogenic arrest (n = 4). Microdeletions of the Y chromosome were found in eight (20%) of the patients with azoospermia. All eight affected patients had interstitial microdeletions within the AZFc subregion. Patients with Sertoli cell-only syndrome had additional microdeletions in regions distal to DAZ (Deleted in Azoospermia), although DAZ deletion was observed in seven of the eight affected patients. In five patients, microdeletions were found in the AZFb region containing RBM (RNA Binding Motif).

CONCLUSION(S)

Our results add to the evidence supporting the current suggestion that there is a cause-and-effect relation between Yq11 microdeletions in the AZF region and azoospermia.

Human male infertility and Y chromosome deletions: role of the AZF-candidate genes DAZ, RBM and DFFRY

Microdeletions in Yq11 overlapping three distinct 'azoospermia factors' (AZFa-c) represent the aetiological factor of 10-15% of idiopathic azoospermia and severe oligozoospermia, with higher prevalence in more severe testiculopathies, such as Sertoli cell-only syndrome. Using a PCR-based screening, we analysed Yq microdeletions in 180 infertile patients affected by idiopathic Sertoli cell-only syndrome and different degrees of hypospermatogenesis, compared with 50 patients with known causes of testicular alteration, 30 with obstructive azoospermia, and 100 normal fertile men. In idiopathic severe testiculopathies (Sertoli cell-only syndrome and severe hypospermatogenesis), a high prevalence of microdeletions (34.5% and 24.7% respectively) was found, while milder forms were not associated with Yq alteration. No deletions were found in testiculopathies of known aetiology, obstructive azoospermia, normal fertile men and male relatives of patients with deletions. Deletions in the AZFc region involving the DAZ gene were the most frequent finding and they were more often observed in severe hypospermatogenesis than in Sertoli cell-only syndrome, suggesting that deletions of this region are not sufficient to cause complete loss of the spermatogenic line. Deletions in AZFb involving the RBM gene were less frequently detected and there was no correlation with testicular phenotype, with an apparent minor role for such gene in spermatogenesis. The DFFRY gene was absent in a fraction of patients, making it a candidate AZFa gene. Our data suggest that larger deletions involving more than one AZF-candidate gene are associated with a more severe testicular phenotype.

Screening for microdeletions of Y chromosome genes in patients undergoing intracytoplasmic sperm injection

The potential of assisted reproduction techniques to transmit genetic defects causing male infertility raises questions concerning the need for a systematic genetic screen and counselling. Deletions of the long arm of the Y chromosome are frequently associated with a failure of spermatogenesis. The search for Y specific sequences and for the gene families RNA binding motif (RBM) and deleted in azoospermia (DAZ) have been introduced in many laboratories. The incidence of Y microdeletions varies widely between studies, from 1-55%. These differences are mainly related to study design. The highest incidence of microdeletions has been reported in well selected idiopathic azoospermic patients. Since microdeletions have been reported also in non-idiopathic patients, it is important to define what is the deletion frequency in unselected patients. We report Y chromosome microdeletion screening in 134 unselected patients undergoing intracytoplasmic sperm injection (ICSI). In the first part of the study we tested six Y chromosome markers. We found three patients with microdeletions (2.2%). Subdivision of the study population revealed a deletion incidence of 4.7% in azoospermic/cryptozoospermic patients; an incidence of 7% in idiopathic patients and an incidence of 16% in idiopathic azoospermic/cryptozoospermic patients. The second part of the study consisted of a screen for the presence of the Y chromosome genes, DBY, CDY, XKRY, eIF-1A, DAZ and BPY2. No additional gene-specific deletions were found. Further data on gene specific screening are needed especially for selected idiopathic patients.

Advances in Y chromosome mapping

The human Y chromosome has long been recognized as being responsible for sex determination. In fact, it also encodes more than 30 genes and gene families that participate in a variety of cellular functions, including bone development, tooth growth, and spermatogenesis. De-novo deletion of Y chromosome segments that contain spermatogenesis genes occurs frequently, resulting in low sperm production and male infertility. This article reviews our current knowledge of the structure and function of the Y chromosome is reviewed.

A long-range restriction map of deletion interval 6 of the human Y chromosome: a region frequently deleted in azoospermic males

Deletion interval 6 (DI6) of the human Y chromosome, located at the distal end of the long arm euchromatic region, is required for normal spermatogenesis. About 10% of males with idiopathic azoospermia or oligospermia have microdeletions in this region. Six gene families, including RBMY (RNA binding motif, Y chromosome), DAZ (deleted in azoospermia), and four recently isolated genes, have been mapped to this interval. Genes from all of these families show testis-specific expression and are thus candidates for azoospermic factor (AZF). DI6 is also rich in Y-specific repetitive sequences, which may be responsible for its frequent deletion. To understand the sequence organization of this region, a 5-Mb restriction map was constructed based on YAC clones and was partially verified on genomic DNA. The locations of five gene family members, as well as numerous STSs, were determined. The map shows several inverted and direct repeats several hundred kilobases in size. The restriction map of DI6 will facilitate future mapping of deletion breakpoints in infertile males and elucidation of mechanisms behind frequent deletions.

Knockout mouse model and gametogenic failure

To evaluate the function of a defined gene in gametogenesis, exciting opportunities are offered by the introduction of techniques to generate knockout mice. In this short article, we briefly describe a few gene knockout mouse models, which show a phenotype that involves impairment of gametogenesis and/or fertility. The focus will be on the mHR6B gene knockout mouse, which shows male infertility. The mHR6B gene encodes an ubiquitin-conjugating enzyme, and the data point to an important role of the ubiquitin pathway in gametogenesis.

Structure and organization of the RBMY genes on the human Y chromosome: transposition and amplification of an ancestral autosomal hnRNPG gene

The RBMY (RNA-binding motif, Y chromosome) gene family encodes a germ-cell-specific nuclear protein implicated in spermatogenesis. It consists of approximately 30 genes and pseudogenes, found on both arms of the Y chromosome. RBMY shares high homology with an autosomal hnRNPG gene that contains an RNA-binding motif and one of the four SRGY repeats found in RBMY. One proposal is that RBMY represents an ancestral hnRNPG gene, transposed to the Y chromosome and then amplified. We characterized seven RBMY genes in interval 6 of the Y chromosome long arm. Four have the normal structure with 12 exons spanning 15 kb, whereas one lacks the first 3 exons, therefore representing a pseudogene. The remaining two genes belong to a different subfamily, resembling the autosomal hnRNPG gene with only one SRGY repeat. We also found that most RBMY genes in interval 6 are arranged in tandem. The structure and organization of the Y-linked RBMY genes support the transposition-amplification hypothesis.