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

hnRNP G/RBMX enhances HPV16 E2 mRNA splicing through a novel splicing enhancer and inhibits production of spliced E7 oncogene mRNAs

Human papillomavirus type 16 (HPV16) E2 is an essential HPV16 protein. We have investigated how HPV16 E2 expression is regulated and have identifed a splicing enhancer that is required for production of HPV16 E2 mRNAs. This uridine-less splicing enhancer sequence (ACGAGGACGAGGACAAGGA) contains 84% adenosine and guanosine and 16% cytosine and consists of three ‘AC(A/G)AGG’-repeats. Mutational inactivation of the splicing enhancer reduced splicing to E2-mRNA specific splice site SA2709 and resulted in increased levels of unspliced E1-encoding mRNAs. The splicing enhancer sequence interacted with cellular RNA binding protein hnRNP G that promoted splicing to SA2709 and enhanced E2 mRNA production. The splicing-enhancing function of hnRNP G mapped to amino acids 236–286 of hnRNP G that were also shown to interact with splicing factor U2AF65. The interactions between hnRNP G and HPV16 E2 mRNAs and U2AF65 increased in response to keratinocyte differentiation as well as by the induction of the DNA damage response (DDR). The DDR reduced sumoylation of hnRNP G and pharmacological inhibition of sumoylation enhanced HPV16 E2 mRNA splicing and interactions between hnRNP G and E2 mRNAs and U2AF65. Intriguingly, hnRNP G also promoted intron retention of the HPV16 E6 coding region thereby inhibiting production of spliced E7 oncogene mRNAs.

Predicted structural differences of four fertility-related Y-chromosome proteins in Macaca mulatta, M. fascicularis, and their Indochinese hybrids

Species in the genus Macaca typically live in multimale-multifemale social groups with male macaques exhibiting some of the largest testis: body weight ratios among primates. Males are believed to experience intense levels of sperm competition. Several spermatogenesis genes are located on the Y-chromosome and, interestingly, occasional hybridization between two species has led to the introgression of the rhesus macaque (Macaca mulatta) Y-chromosome deep into the range of the long-tailed macaque (M. fascicularis). These observations have led to the prediction that the successful introgression of the rhesus Y-haplotype is due to functional differences in spermatogenesis genes compared to those of the native long-tailed Y-haplotype. We examine here four Y-chromosomal loci-RBMY, XKRY, and two nearly identical copies of CDY-and their corresponding protein sequences. The genes were surveyed in representative animals from north of, south of, and within the rhesus x long-tailed introgression zone. Our results show a series of non-synonymous amino acid substitutions present between the two Y-haplotypes. Protein structure modeling via I-TASSER revealed different folding patterns between the two species' Y-proteins, and functional predictions via TreeSAAP further reveal physicochemical differences as a result of non-synonymous substitutions. These differences inform our understanding of the evolution of primate Y-proteins involved in spermatogenesis and, in turn, have biomedical implications for human male fertility.

Genes located in Y-chromosomal regions important for male fertility show altered transcript levels in cryptorchidism and respond to curative hormone treatment

Background

Undescended (cryptorchid) testes in patients with defective mini-puberty and low testosterone levels contain gonocytes that fail to differentiate normally, which impairs the development of Ad spermatogonia and ultimately leads to adult infertility. Treatment with the gonadotropin-releasing hormone agonist GnRHa increases luteinizing hormone and testosterone and rescues fertility in the majority of pathological cryptorchid testes. Several Y-chromosomal genes in the male-specific Y region (MSY) are essential for spermatogenesis, testis development and function, and are associated with azoospermia, infertility and cryptorchidism. In this study, we analyzed the expression of MSY genes in testes with Ad spermatogonia (low infertility risk patients) as compared to testes lacking Ad spermatogonia (high infertility risk) before and after curative GnRHa treatment, and in correlation to their location on the Y-chromosome.

Results

Twenty genes that are up- or down-regulated in the Ad- group are in the X-degenerate or the ampliconic region, respectively. GnRHa treatment increases mRNA levels of 14 genes in the ampliconic region and decreases mRNA levels of 10 genes in the X-degenerate region.

Conclusion

Our findings implicate Y-chromosomal genes, including USP9Y, UTY, TXLNGY, RBMY1B, RBMY1E, RBMY1J and TSPY4, some of which are known to be important for spermatogenesis, in the curative hormonal treatment of cryptorchidism-induced infertility.

Spermatogenic failure and the Y chromosome

The Y chromosome harbors a number of genes essential for testis development and function. Its highly repetitive structure predisposes this chromosome to deletion/duplication events and is responsible for Y-linked copy-number variations (CNVs) with clinical relevance. The AZF deletions remove genes with predicted spermatogenic function en block and are the most frequent known molecular causes of impaired spermatogenesis (5-10% of azoospermic and 2-5% of severe oligozoospermic men). Testing for this deletion has both diagnostic and prognostic value for testicular sperm retrieval in azoospermic men. The most dynamic region on the Yq is the AZFc region, presenting numerous NAHR hotspots leading to partial losses or gains of the AZFc genes. The gr/gr deletion (a partial AZFc deletion) negatively affects spermatogenic efficiency and it is a validated, population-dependent risk factor for oligozoospermia. In certain populations, the Y background may play a role in the phenotypic expression of partial AZFc rearrangements and similarly it may affect the predisposition to specific deletions/duplication events. Also, the Yp contains a gene array, TSPY1, with potential effect on germ cell proliferation. Despite intensive investigations during the last 20 years on the role of this sex chromosome in spermatogenesis, a number of clinical and basic questions remain to be answered. This review is aimed at providing an overview of the role of Y chromosome-linked genes, CNVs, and Y background in spermatogenesis.

Cardiac stem cell therapy for cardiac repair

The discovery of adult cardiac stem cells (CSCs) and their potential to restore functional cardiac tissue has fueled unprecedented interest in recent years. Indeed, stem-cell–based therapies have the potential to transform the treatment and prognosis of heart failure, for they have the potential to eliminate the underlying cause of the disease by reconstituting the damaged heart with functional cardiac cells. Over the last decade, several independent laboratories have demonstrated the utility of c-kit+/Lin- resident CSCs in alleviating left ventricular dysfunction and remodeling in animal models of acute and chronic myocardial infarction. Recently, the first clinical trial of autologous CSCs for treatment of heart failure resulting from ischemic heart disease (Stem Cell Infusion in Patients with Ischemic cardiOmyopathy [SCIPIO]) has been conducted, and the interim results are quite promising. In this phase I trial, no adverse effects attributable to the CSC treatment have been noted, and CSC-treated patients showed a significant improvement in ejection fraction at 1 year (+13.7 absolute units versus baseline), accompanied by a 30.2 % reduction in infarct size. Moreover, the CSC-induced enhancement in cardiac structure and function was associated with a significant improvement in the New York Heart Association (NYHA) functional class and in the quality of life, as measured by the Minnesota Living with Heart failure Questionnaire. These results are exciting and warrant larger, phase II studies. However, CSC therapy for cardiac repair is still in its infancy, and many hurdles need to be overcome to further enhance the therapeutic efficacy of CSCs.

c-kit+ Cardiac stem cells alleviate post-myocardial infarction left ventricular dysfunction despite poor engraftment and negligible retention in the recipient heart

Although transplantation of c-kit+ cardiac stem cells (CSCs) has been shown to alleviate left ventricular (LV) dysfunction induced by myocardial infarction (MI), the number of exogenous CSCs remaining in the recipient heart following transplantation and their mechanism of action remain unclear. We have previously developed a highly sensitive and accurate method to quantify the absolute number of male murine CSCs in female recipient organs after transplantation. In the present study, we used this method to monitor the number of donor CSCs in the recipient heart after intracoronary infusion. Female mice underwent a 60-min coronary occlusion followed by reperfusion; 2 days later, 100,000 c-kit+/lin- syngeneic male mouse CSCs were infused intracoronarily. Only 12.7% of the male CSCs present in the heart immediately (5 min) after infusion were still present in the heart at 24 h, and their number declined rapidly thereafter. By 35 days after infusion, only ∼1,000 male CSCs were found in the heart. Significant numbers of male CSCs were found in the lungs and kidneys, but only in the first 24 h. The number of CSCs in the lungs increased between 5 min and 24 h after infusion, indicating recirculation of CSCs initially retained in other organs. Despite the low retention and rapid disappearance of CSCs from the recipient heart, intracoronary delivery of CSCs significantly improved LV function at 35 days (Millar catheter). These results suggest that direct differentiation of CSCs alone cannot account for the beneficial effects of CSCs on LV function; therefore, paracrine effects must be the major mechanism. The demonstration that functional improvement is dissociated from survival of transplanted cells has major implications for our understanding of cell therapy. In addition, this new quantitative method of stem cell measurement will be useful in testing approaches of enhancing CSC engraftment and survival after transplantation.

Expression analysis of RNA-binding motif gene on Y chromosome (RBMY) protein isoforms in testis tissue and a testicular germ cell cancer-derived cell line (NT2)

BACKGROUND

RNA-binding motif gene on Y chromosome (RBMY), a germ cell-specific nuclear protein, is known as a key factor in spermatogenesis and disorders associated with this protein have been recognized to be related to male infertility. Although it was suggested that this protein could have different functions during germ cell development, no studies have been conducted to uncover the mechanism of this potential function yet. Here, we analyzed the expression pattern of RBMY protein isoforms in testis compared to NT2, a testicular germ cell cancer-derived cell line, to test probability of differential expression of RBMY protein isoforms at different spermatogenesis stages.

METHODS

Full length and a segment of RBMY gene were cloned and expressed in E. coli. Anti-human RBMY antibody was produced in rabbit using the recombinant proteins as antigen. Western-blot and immunofluorescence were conducted for detection and comparison of RBMY protein isoforms.

RESULTS

Selected segment of RBMY protein resulted in producing a mono-specific antibody. As results shows, only the longest isoform of RBMY was expressed at protein level in NT2 cell line, while three isoforms of this protein were detected in the whole testis lysate.

CONCLUSION

The results imply that different alternative splicing may happen in testis cells and probably difference of RBMY function during spermatogenesis is due to the differential expression of RBMY protein isoforms. These results and further experiments on RBMY isoforms can help to obtain a better understanding of the function of this protein, which may increase our knowledge about spermatogenesis and causes of male infertility.

Cellular ontogeny of RBMY during human spermatogenesis and its role in sperm motility

The Y-chromosome-encoded gene RBMY (RNA-binding motif on Y) is a male germline RNA-binding protein and is postulated to be a RNA-splicing regulator. In order to understand the roles of RBMY in different stages of male gamete maturation, the present study aimed at determining its cellular expression during spermatogenesis, spermeogenesis and in mature spermatozoa. In the spermatogonia (cKIT-positive cells), RBMY immunolocalized as two distinct foci, one in the nucleolus and the other in the subnuclear region; in the spermatocytes (cKIT-negative cells), the nucleus had punctuate staining with a subnuclear foci; in the pachytene cells, the protein was localized as a punctuate pattern in the nucleus spread along the elongating chromosomes. In the round and the elongating spermatids, the protein expression was polarized and restricted to the cytoplasm and in the developing mid-piece. In testicular and ejaculated sperm, RBMY was localized to the mid-piece region and weakly in the tail. Incubation of spermatozoa with the RBMY antibody reduced its motility. The spatial differences in expression of RBMY in the germ cells and the presences of this protein in post-meiotic cells and in transcriptionally inert spermatozoa suggest its involvement in multiple functions beyond RNA splicing. One such possible function of RBMY could be its involvement in sperm motility.

A highly sensitive and accurate method to quantify absolute numbers of c-kit+ cardiac stem cells following transplantation in mice

Although transplantation of c-kit+ cardiac stem cells (CSCs) alleviates post-myocardial infarction left ventricular dysfunction, there are no reliable methods that enable measurement of the absolute number of CSCs that persist in the recipient heart. To overcome this limitation, we developed a highly sensitive and accurate method to quantify the absolute number of murine CSCs after transplantation. This method has two unique features: (1) real-time PCR-based detection of a novel male-specific, multiple-copy gene, Rbmy, which significantly increases the sensitivity of detection of male donor cells in a female recipient, and (2) an internal standard, which permits quantification of the absolute number of CSCs as well as the total number of cells in the recipient organ. Female C57BL/6 mice underwent coronary occlusion and reperfusion; 2 days later, 10(5) male mouse CSCs were injected intramyocardially. Tissues were analyzed by real-time PCR at serial time points. In the risk region, >75 % of CSCs present at 5 min were lost in the ensuing 24 h; only 7.6 ± 2.1 % of the CSCs present at 5 min could still be found at 7 days after transplantation and only 2.8 ± 0.5 % (i.e., 1,224 ± 230 cells/heart) at 35 days. Thus, even after direct intramyocardial injection, the total number of CSCs that remain in the murine heart is minimal (at 24 h, ~10 % of the cells injected; at 35 days, ~1 %). This new quantitative method of stem cell detection, which enables measurement of absolute cell number, should be useful to optimize cell-based therapies, not only for CSCs but also for other stem cells and other organs.

Sex, rebellion and decadence: the scandalous evolutionary history of the human Y chromosome

It can be argued that the Y chromosome brings some of the spirit of rock&roll to our genome. Equal parts degenerate and sex-driven, the Y has boldly rebelled against sexual recombination, one of the sacred pillars of evolution. In evolutionary terms this chromosome also seems to have adopted another of rock&roll's mottos: living fast. Yet, it appears to have refused to die young. In this manuscript the Y chromosome will be analyzed from the intersection between structural, evolutionary and functional biology. Such integrative approach will present the Y as a highly specialized product of a series of remarkable evolutionary processes. These led to the establishment of a sex-specific genomic niche that is maintained by a complex balance between selective pressure and the genetic diversity introduced by intrachromosomal recombination. Central to this equilibrium is the "polish or perish" dilemma faced by the male-specific Y genes: either they are polished by the acquisition of male-related functions or they perish via the accumulation of inactivating mutations. Thus, understanding to what extent the idiosyncrasies of Y recombination may impact this chromosome's role in sex determination and male germline functions should be regarded as essential for added clinical insight into several male infertility phenotypes. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

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.

Identifying mRNAs bound by human RBMY protein in the testis

Rbmy gene encodes a germ-cell specific nuclear RNA-binding protein and is involved in spermatogenesis. To further investigate the specific events of spermatogenesis in which Rbmy plays a role, the target mRNAs of human RBMY protein were isolated and identified. Through the isolating specific nucleic acids associated with proteins (SNAAP) technique, we isolated twenty potential target genes of human RBMY protein from the human testis in the present study. Some of these target genes play important roles during spermatogenesis and have alternative transcripts in the testis. In this study, we focused on the human- related (never in mitosis gene a) kinase 10 (Nek10) gene, which belongs to the Nek protein kinase subfamily. Nek10 has two transcripts, and the results of RT-PCR and Electrophoretic Mobility Shift Assays (EMSA) show that hRBMY protein can only bind to transcript variant 2 of Nek10 and that hRbmy may take part in alternative splicing of Nek10. Isolation and identification of target genes of hRBMY will be helpful to further investigate the biological function of RBMY in spermatogenesis.

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.

The origin and evolution of human ampliconic gene families and ampliconic structure

Out of the nine male-specific gene families in the human Y chromosome amplicons, we investigate the origin and evolution of seven families for which gametologous and orthologous sequences are available. Proto-X/Y gene pairs in the original mammalian sex chromosomes played major roles in origins and gave rise to five gene families: XKRY, VCY, HSFY, RBMY, and TSPY. The divergence times between gametologous X- and Y-linked copies in these families are well correlated with the former X-chromosomal locations. The CDY and DAZ families originated exceptionally by retroposition and transposition of autosomal copies, respectively, but CDY possesses an X-linked copy of enigmatic origin. We also investigate the evolutionary relatedness among Y-linked copies of a gene family in light of their ampliconic locations (palindromes, inverted repeats, and the TSPY array). Although any pair of copies located at the same arm positions within a palindrome is identical or nearly so by frequent gene conversion, copies located at different arm positions are distinctively different. Since these and other distinct copies in various gene families were amplified almost simultaneously in the stem lineage of Catarrhini, we take these simultaneous amplifications as evidence for the elaborate formation of Y ampliconic structure. Curiously, some copies in a gene family located at different palindromes exhibit high sequence similarity, and in most cases, such similarity greatly extends to repeat units that harbor these copies. It appears that such palindromic repeat units have evolved by and large en bloc, but they have undergone frequent exchanges between palindromes.

Polymorphismes du chromosome Y et fertilité masculine

Molecular anomalies of the Y chromosome leading to male infertility are mainly microdeletions of the long arm of the Y chromosome. Three recurrently deleted portions of the long arm are the AZFa, AZFb and AZFc (AZF: Azoospermia Factor) regions. Complete deletions of the AZFc region are found in 10% of cases of severe male infertility. In addition to the AZF deletions, certain classes of Y chromosome (haplogroups) may also predispose to male infertility and could be transmitted to future male descents by various Assisted Reproductive Techniques (ART). Since the first discovery of microdeletions, the sequence of the Y chromosome has become available, revealing the mechanisms underlying deletion formation and also resulting in a coherent screening strategy. Recently, partial deletions of the AZF regions have been described. The significance of these deletions in the clinical context remains to be defined.

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.

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.

A fiber-FISH contig spanning the non-recombining region of the human Y chromosome

Using fluorescence in-situ hybridization on interphase chromatin fibers (fiber-FISH), we have constructed an overlapping fiber-FISH contig spanning the non-recombining region of the human Y chromosome (NRY). We first established a standard FISH-signal pattern for a distinct panel of DNA clones on prometaphase Y chromosomes in six healthy fertile men. Clones in the panel were selected from all R-bands as well as deletion intervals 1 through 7 plus PAR1 and PAR2 of the human Y chromosome. We next used signals of these marker clones to build a fiber-FISH contig for the multicopy gene families, CDY, DAZ, RBMY, TSPY and XKRY, along the NRY. Our fiber-FISH contig of human NRY may help to close the four gaps that still exist in the current physical map of the human Y chromosome. Furthermore, it provides a more complete picture with respect to the positions and arrangements of the multicopy gene families along the human NRY.

Male reproductive function and the human Y chromosome: is selection acting on the Y?

The human Y chromosome encodes genes that are essential for male sex determination, spermatogenesis and protection against Turner stigmata. In recent years mutations have been identified in Y-chromosome genes associated with these phenotypes and a series of microdeletions of the long arm of the Y have been defined that are specifically associated with male infertility. In parallel, the discovery of polymorphic markers on the Y, comprising of both slow-mutating binary markers and rapidly-mutating microsatellites, has enabled the high resolution definition of a large number of paternal lineages (haplogroups). These Y-chromosome haplogroups have been extensively used to trace population movements and understand human origins and histories, but recently a growing number of association studies have been performed aimed at assessing the relationship between the Y-chromosome background and Y-linked phenotypes such as infertility and male-specific cancers. These preliminary studies, comparing haplogroup distributions between case and control populations, are promising and suggest an association between different Y-chromosome lineages, sperm counts and prostate cancer. However, we highlight the need to extend these studies to other world populations. Increased sample numbers and a better haplogroup resolution using additional binary markers in association studies are necessary. By these approaches novel associations between Y-chromosome haplotypes and disease may be revealed and the degree to which selection is acting on the human Y chromosome may be determined.

Characterization of the OFD1/Ofd1 genes on the human and mouse sex chromosomes and exclusion of Ofd1 for the Xpl mouse mutant

Oral-facial-digital type 1 (OFD1) syndrome is an X-linked dominant condition characterized by malformations of the face, oral cavity, and digits. The responsible gene, OFD1, maps to human Xp22 and has an unknown function. We isolated and characterized the mouse Ofd1 gene and showed that it is subject to X-inactivation, in contrast to the human gene. Furthermore, we excluded a role for Ofd1 in the pathogenesis of the spontaneous mouse mutant Xpl, which had been proposed as a mouse model for this condition. Comparative sequence analysis demonstrated that OFD1 is conserved among vertebrates and absent in invertebrates. This analysis allowed the identification of evolutionarily conserved domains in the protein. Finally, we report the identification of 18 apparently nonfunctional OFD1 copies, organized in repeat units on the human Y chromosome. These degenerate OFD1-Y genes probably derived from the ancestral Y homologue of the X-linked gene. The high level of sequence identity among the different units suggests that duplication events have recently occurred during evolution.

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.

VCY2 protein interacts with the HECT domain of ubiquitin-protein ligase E3A

VCY2 locates in the AZFc region on chromosome Yq and is frequently deleted in infertile men with severe oligozoospermia or azoospermia. VCY2 is a testis-specific protein with unknown function. This study was to identify the protein that interacts with VCY2. We used the full-length VCY2 as bait to screen the human testis cDNA library using yeast two-hybrid approach. We identified a number of positive-interacting clones that encode ubiquitin-protein ligase E3A (UBE3A). UBE3A contains a HECT domain that binds VCY2. The specificity of the interaction was confirmed by co-immunoprecipitation and yeast mating. Northern blot analyses revealed two UBE3A transcripts 1.4 and 2kb that were abundantly expressed in human testis. We also showed that both VCY2 and UBE3A mRNAs were expressed in ejaculated human spermatozoa, indicating that both genes localize in the germ cell compartment. These data suggest that UBE3A ubiquitination may be required for VCY2 function.

Y chromosome microdeletions and male infertility

Classical cytogenetic mapping has identified a locus on the long arm of the human Y chromosome that is required for spermatogenesis and is termed AZF, an acronym for the hypothetical azoospermia factor encoded by this locus. Recent molecular attempts to identify the gene corresponding to this locus have revealed that there are at least three genes in three separate microdeletion intervals. Two of these microdeletion intervals contain genes encoding proteins with potential roles in RNA metabolism. These genes are members of Y-encoded gene families with autosomal homologues. The cell biology of one of these genes, RBM (an acronym of RNA binding motif), is complex and suggests a role in pre-mRNA splicing.

Local regulation of spermatogenesis: a living cell approach

The normal function of the testis is dependent on stimulation by pituitary gonadotrophins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Targets for these hormones are Leydig cells in the interstitial tissue, and Sertoli cells in the seminiferous epithelium, respectively. The effect of LH on the seminiferous epithelium is mediated by testosterone produced by the Leydig cells. Therefore, the two main hormones that influence the function of the seminiferous epithelium directly are FSH and testosterone. The preferential action of FSH in the adult seminiferous epithelium is associated with stages that involve meiotic divisions and early spermiogenesis. The parameters related to androgen action predominate at different stages during which the final maturation of the spermatids, spermiation and the onset of meiosis take place. The stage-dependent variation of the hormone responses in the seminiferous epithelium indicates the presence of local paracrine regulation and cell interaction mechanisms in the seminiferous epithelium, which are dependent on the spermatogenic cells associated with the Sertoli cells. Several growth factors have been suggested as mediators of this interaction. Owing to its highly complex structure, the seminiferous epithelium has been a difficult area for biochemical studies. New in vitro techniques have made these studies possible, and particular advances have been made using recombinant DNA techniques and transgene technology.

Reduced copy number of DAZ genes in subfertile and infertile men

OBJECTIVE(S)

To determine the copy number and identity of the DAZ genes on the Y chromosomes of infertile patients.

DESIGN

Prospective study.

SETTING

University medical center.

PATIENT(S)

One hundred and thirty-nine patients with male factor infertility.

INTERVENTION(S)

The separate genes were detected by polymerase chain reaction (PCR) digestion assays of sequence family variants in leukocyte DNA and by fluorescence in situ hybridization of interphase nuclei and chromatin fibers.

MAIN OUTCOME MEASURE(S)

Number of DAZ genes present.

RESULT(S)

One hundred twenty-nine patients had four genes, 6 patients had two genes, and 4 patients had none. Three patients had a deletion of the two proximal DAZ genes, and three were missing both distal genes. Semen analysis showed a less severe phenotype in patients with only two DAZ genes compared with patients missing all four genes.

CONCLUSION(S)

In six patients, two different partial deletions were found that were not detected by PCR with conventional markers. One patient with an AZFb deletion appeared to also have a partial AZFc deletion that was not detected by routine PCR. Phenotypic differences between patients with different deletions suggest a dose effect of the DAZ genes.

The AZFc region of the Y chromosome features massive palindromes and uniform recurrent deletions in infertile men

Deletions of the AZFc (azoospermia factor c) region of the Y chromosome are the most common known cause of spermatogenic failure. We determined the complete nucleotide sequence of AZFc by identifying and distinguishing between near-identical amplicons (massive repeat units) using an iterative mapping-sequencing process. A complex of three palindromes, the largest spanning 3 Mb with 99.97% identity between its arms, encompasses the AZFc region. The palindromes are constructed from six distinct families of amplicons, with unit lengths of 115-678 kb, and may have resulted from tandem duplication and inversion during primate evolution. The palindromic complex contains 11 families of transcription units, all expressed in testis. Deletions of AZFc that cause infertility are remarkably uniform, spanning a 3.5-Mb segment and bounded by 229-kb direct repeats that probably served as substrates for homologous recombination.

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.

New uses for new haplotypes the human Y chromosome, disease and selection

Recent discoveries of many new genes have made it clear that there is more to the human Y chromosome than a heap of evolutionary debris, hooked up to a sequence that happens to endow its bearer with testes. Coupled with the recent development of new polymorphic markers on the Y, making it the best-characterized haplotypic system in the genome, this gives us new opportunities to assess its role in disease and selection, through association studies with phenotypes such as infertility and cancers. However, the peculiar genetics of this bizarre chromosome means that we should interpret such studies particularly cautiously.

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.

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.

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.