Degeneracy in human multicopy RBM (YRRM), a candidate spermatogenesis gene

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.

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.

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.

Analysis of population structures of viral isolates using single-strand conformation polymorphism method

The analysis of viral populations requires the use of techniques that describe characteristics of individuals. The single-strand conformation polymorphism (SSCP) makes possible the identification of genetic differences between viral sequences and constitutes an alternative to the expensive and time-consuming cloning and sequencing strategies. Applied to small genomic regions (from 100 to 500 bases in length), SSCP patterns could describe, under appropriate experimental conditions, single nucleotide variations in the studied sequence. The different steps of a complete SSCP procedure, from sampling to pattern analysis (including nucleic acid extraction, RT-PCR amplification, double-stranded DNA quantification, polyacrylamide gel preparation, electrophoresis conditions, and staining procedures), are described using a region (500 bases) of the barley yellow dwarfvirus-PAV (BYDV-PAV, Luteovirus) genome as molecular target.

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.

AZF deletions and Y chromosomal haplogroups: history and update based on sequence

AZF deletions are genomic deletions in the euchromatic part of the long arm of the human Y chromosome (Yq11) associated with azoospermia or severe oligozoospermia. Consequently, it can be assumed that these deletions remove Y chromosomal genes required for spermatogenesis. However, these 'classical' or 'complete' AZF deletions, AZFa, AZFb and AZFc, represent only a subset of rearrangements in Yq11. With the benefit of the Y chromosome sequence, more rearrangements (deletions, duplications, inversions) inside and outside the classical AZF deletion intervals have been elucidated and intra-chromosomal non-allelic homologous recombinations (NAHRs) of repetitive sequence blocks have been identified as their major cause. These include duplications in AZFa, AZFb and AZFc and the partial AZFb and AZFc deletions of which some were summarized under the pseudonym 'gr/gr' deletions. At least some of these rearrangements are associated with distinct Y chromosomal haplogroups and are present with similar frequencies in fertile and infertile men. This suggests a functional redundancy of the AZFb/AZFc multi-copy genes. Alternatively, the functional contribution(s) of these genes to human spermatogenesis might be different in men of different Y haplogroups. That raises the question whether, the frequency of Y haplogroups with different AZF gene contents in distinct human populations leads to a male fertility status that varies between populations or whether, the presence of the multiple Y haplogroups implies a balancing selection via genomic deletion/amplification mechanisms.

Genomic heterogeneity and instability of the AZF locus on the human Y chromosome

The spermatogenesis locus azoospermia factor (AZF) in Yq11 has been mapped to three microdeletion intervals designated as AZFa, AZFb, and AZFc. They are caused by intrachromosomal recombination events between large homologous repetitive sequence blocks, and AZFc microdeletions are now recognised as the most frequent known genetic lesion causing male infertility. However, in the same Y-region, large genomic heterogeneities are also observed in fertile men, and only complete AZFa and AZFb deletions are associated with a specific testicular pathology. Partial AZF deletions are associated with variable pathologies and partial AZFc deletions may even have no impact on male fertility. This suggests a genetic redundancy of the multi-copy genes in AZFb and AZFc and a causative relationship between the occurrence of first microdeletions then macrodeletions in the repetitive structure of Yq11 where large palindromes are probably promoting multiple gene conversions and AZF rearrangements.

Scanning of Y-chromosome azoospermia factors loci using real-time polymerase chain reaction and melting curve analysis

OBJECTIVE

To develop a novel method to scan AZF loci looking for microdeletions.

DESIGN

Molecular method development.

SETTING

Men undergoing reproductive techniques in a private fertility unit. Molecular methods were performed in a private center for biomedical research.

PATIENT(S)

: Fifty-eight men divided in two groups depending on seminal analyses. A group of 19 women were also included as positive controls (absence of amplification).

INTERVENTION(S)

Peripheral blood extraction and DNA purification.

MAIN OUTCOME MEASURE(S)

Our method is based on real-time polymerase chain reaction (PCR) and melting curve analysis. We performed the screening of 16 selected sequence tagged sites (STS) within AZF loci, and we also calculated the mean, range, and standard deviation for melting temperature patterns and the crossing points values for each STS tested.

RESULT(S)

We detected one azoospermic patient with several STS deleted within the AZFc region. No deletions were detected in a group of 13 healthy men, and no amplification for any of the STS tested were observed in the positive control group (19 healthy women).

CONCLUSION(S)

We have developed a novel method based on real-time PCR and melting curve analysis to scan AZF loci looking for microdeletions This method is fast and reliable and permits the scanning of DNA from one patient per hour, minimizing the risk of cross contamination, and false-positive and false-negative results.

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.

Polymorphic DAZ gene family in polymorphic structure of AZFc locus: Artwork or functional for human spermatogenesis?

Human spermatogenesis is regulated by a network of genes located on autosomes and on sex chromosomes, but especially on the Y chromosome. Most results concerning the germ cell function of the Y genes were obtained by genomic breakpoint mapping studies of the Y chromosome of infertile patients. Although this approach has the benefit of focussing on those Y regions that contain most likely the Y genes of functional importance, its major drawback is the fact that fertile control samples were often missing. In fertile men, molecular and cytogenetic analyses of the Y chromosome has revealed highly polymorphic chromatin domains especially in the distal euchromatic part (Yq11.23) and in the heterochromatic part (Yq12) of the long arm. In sterile patients cytogenetic analyses mapped microscopically visible Y deletions and rearrangements in the same polymorphic Y regions. The presence of a Y chromosomal spermatogenesis locus was postulated to be located in Yq11.23 and designated as AZoospermia Factor (ZF). More recently, molecular deletion mapping in Yq11 has revealed a series of microdeletions that could be mapped to one of three different AZF loci: AZFa in proximal Yq11 (Yq11.21), AZFb and AZFc in two non-overlapping Y-regions in distal Yq11 (Yq11.23). This view was supported by the observation that AZFa and AZFb microdeletions were associated with a specific pathology in the patients' testis tissue. Only AZFc deletions were associated with a variable testicular pathology and in rare cases AZFc deletions were even found inherited from father to son. However, AZFc deletions were found with a frequency of 10-20% only in infertile men and most of them were proved to be "de novo", i.e. the AZFc deletion was restricted to the patient's Y chromosome. Based mainly on positional cloning experiments of testis cDNA clones and on the Y chromosomal sequence now published in GenBank, a first blueprint for the putative gene content of the AZFc locus can now be given and the gene location compared to the polymorphic DNA domains. This artwork of repetitive sequence blocks called AZFc amplicons raised the question whether the AZFc chromatin is still part of the heterochromatic domain of the Y long arm well known for its polymorphic extensions or is decondensed and part of the Yq11.23 euchromatin? We discuss also the polymorphic DAZ gene family and disclose putative origins of its molecular heterogeneity in fertile and infertile men recently identified by the analyses of Single Nucleotide Variants (SNVs) in this AZFc gene locus.

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.

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.

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.

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.

TSPY variants in six loci on the human Y chromosome

We have studied the structure, organization, and evolution of the human TSPY gene family by mapping three sequence variants identified through RT-PCR analysis onto genomic clones derived from two different YAC contigs. TSPY gene family members occur in at least six locations on the human Y chromosome, and each cluster contains a unique combination of variants. Our data further suggest that an 18-bp tandem duplication found in TSPY exon 1 originated from an unequal sister chromatid exchange between two tandemly arranged TSPY clusters.

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.

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.

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.

Understanding the genes involved in spermatogenesis: a progress report

OBJECTIVE

To review the current literature on genes known to affect fertility in the human and mouse.

DESIGN

A literature review was performed and key articles were chosen for focus in the areas of genes with effects only on spermatogenesis and oogenesis, with an emphasis on Y-chromosome-encoded gene families and spermatogenesis. In addition, studies describing genes deleted in transgenic mice were incorporated.

RESULT(S)

Several gene families on the Y chromosome are implicated in spermatogenic failure, but the link between the genetic lesion and the resulting defect is unclear. Many mouse genes involved in repair and DNA damage monitoring have specific effects on gametogenesis in and around meiosis.

CONCLUSION(S)

Many genes are involved only in gametogenesis, and some of these are beginning to be understood in terms of their functions. An even larger number of genes is required for gametogenesis, and other functions and mouse models give insights important for human disease.

Dynamic changes in the subnuclear organisation of pre-mRNA splicing proteins and RBM during human germ cell development

RBM is a germ-cell-specific RNA-binding protein encoded by the Y chromosome in all mammals, implying an important and evolutionarily conserved (but as yet unidentified) function during male germ cell development. In order to address this function, we have developed new antibody reagents to immunolocalise RBM in the different cell types in the human testis. We find that RBM has a different expression profile from its closest homologue hnRNPG. Despite its ubiquitous expression in all transcriptionally active germ cell types, RBM has a complex and dynamic cell biology in human germ cells. The ratio of RBM distributed between punctate nuclear structures and the remainder of the nucleoplasm is dynamically modulated over the course of germ cell development. Moreover, pre-mRNA splicing components are targeted to the same punctate nuclear regions as RBM during the early stages of germ cell development but late in meiosis this spatial association breaks down. After meiosis, pre-mRNA splicing components are differentially targeted to a specific region of the nucleus. While pre-mRNA splicing components undergo profound spatial reorganisations during spermatogenesis, neither heterogeneous ribonucleoproteins nor the transcription factor Sp1 show either developmental spatial reorganisations or any specific co-localisation with RBM. These results suggest dynamic and possibly multiple functions for RBM in germ cell development.

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.

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

The RBM (RNA-binding motif) gene family on the human Y chromosome encodes proteins with an RNA-binding domain. Its exclusive expression in germ cells and its partial deletion in some azoospermic or severely oligospermic males provide evidence of a role for RBM genes in spermatogenesis. There are approximately 30 RBM genes, found on both arms of the Y chromosome. Two RBM cDNA clones with slightly different sequences have been reported. To investigate the number of functional genes, we studied RBM expression by use of RT-PCR of RBM transcripts and by characterizing numerous RBM cDNA clones. A total of 27 RT-PCR and 19 cDNA clones were sequenced. Whereas the RT-PCR clones pointed to the existence of at least six RBM subfamilies (RBMI to RBMVI), the cDNA clones indicated that only RBMI is actively transcribed and encodes functional proteins. A total of six RBMI genes were identified, which produce four polypeptides due to some silent base substitutions. The transcripts of each gene are alternatively spliced to generate protein isoforms with three or four SRGY boxes, thus greatly increasing the complexity of the products of the RBM gene family. We also provide evidence suggesting that a 5-bp deletion in a previously reported RBM cDNA clone represents a processing irregularity.

Expression of RBM in the nuclei of human germ cells is dependent on a critical region of the Y chromosome long arm

The association of abnormal spermatogenesis in men with Y chromosome deletions suggests that genes important for spermatogenesis have been removed from these individuals. Recently, genes encoding two putative RNA-binding proteins (RBM and DAZ/SPGY) have been mapped to two different regions of the human Y chromosome. Both of these genes encode proteins that contain a single RNA recognition motif and a (different) internally repeating sequence. Y-linked RBM homologues are found in all mammalian species. We have raised an antiserum to RBM and used it to show that RBM is a nuclear protein expressed in fetal, prepubertal, and adult male germ cells. The distribution of RBM protein in the adult correlates with the pattern of transcriptional activity in spermatogenesis, suggesting that RBM is involved in the nuclear metabolism of newly synthesized RNA. RBM sequences are found on both arms of the Y chromosome making genotype-phenotype correlations difficult for this gene family. To address the location of the functional genes and the consequences of their deletion, we examined a panel of men with Y chromosome deletions and known testicular pathologies using this antiserum. This approach enabled us to map a region of the Y chromosome essential for RBM expression. In the absence of detectable RBM expression we see stages of germ cell development up to early meiosis, but not past this point into the haploid phase of spermatogenesis.