Mice with Y chromosome deletion and reduced Rbm genes on a heterozygous Dazl1 null background mimic a human azoospermic factor phenotype

A subset of azoospermia or oligozoospermia patients have microdeletions in defined regions of their Y chromosome, namely the AZFa, b, and c regions. Candidate genes in humans that may cause the azoospermia factor (AZF) phenotype have been assigned to these regions and can include the DAZ and RBM genes. Part of the variability in the AZFc phenotype might be due to interaction between the effects of deleting the DAZ and RBM genes. We mimicked human deletions of RBM and DAZ in the mouse by crossing male mice with a deleted Y chromosome with a reduced number of Rbm genes (Y(d1)) to heterozygote Dazl1 null female mice to study the interaction of the Dazl1 and Rbm or other genes located in the Y(d1) deletion interval. Dazl-/+ Y(d1) animals showed a significant reduction in the sperm count (P < 0.001), an increase of abnormal sperm heads and prominent mid-piece defects of the tails compared to either mutation alone (P < 0.001). Hence, Dazl1 and the genes removed on the Y(d1) chromosome are active in different pathways contributing to different stages of spermatogenesis. Reduction of Dazl1 and Rbm genes as well as/or deletion of the Y chromosome in mice gives rise to a phenotype similar to the heterogeneous AZFc phenotype observed in humans.     

Characterisation of the coding sequence and fine mapping of the human DFFRY gene and comparative expression analysis and mapping to the Sxrb interval of the mouse Y chromosome of the Dffry gene

DFFRY (the Y-linked homologue of the DFFRX Drosophila fat-facets related X gene) maps to proximal Yq11.2 within the interval defining the AZFa spermatogenic phenotype. The complete coding region of DFFRY has been sequenced and shows 89% identity to the X-linked gene at the nucleotide level. In common with DFFRX , the potential amino acid sequence contains the conserved Cys and His domains characteristic of ubiquitin C-terminal hydrolases. The human DFFRY mRNA is expressed in a wide range of adult and embryonic tissues, including testis, whereas the homologous mouse Dffry gene is expressed specifically in the testis. Analysis of three azoospermic male patients has shown that DFFRY is deleted from the Y chromosome in these individuals. Two patients have a testicular phenotype which resembles Sertoli cell-only syndrome, and the third diminished spermatogenesis. In all three patients, the deletions extend from close to the 3' end into the gene, removing the entire coding sequence of DFFRY. The mouse Dffry gene maps to the Sxrb deletion interval on the short arm of the mouse Y chromosome and its expression in mouse testis can first be detected between 7.5 and 10.5 days after birth when type A and B spermatogonia and pre-leptotene and leptotene spermatocytes are present.      

Decreased expression of mouse Rbm3, a cold-shock protein, in Sertoli cells of cryptorchid testis

Physiological scrotal hypothermia is necessary for normal spermatogenesis and fertility in mammals. Human RNA binding motif protein 3 (RBM3) is structurally highly similar to the cold-inducible RNA-binding protein (Cirp), and both mRNAs are induced in human cells at the scrotal temperature (32 degrees C). We report here the cloning of mouse Rbm3 cDNA, which encoded an 18-kd protein with 94% identity in amino acid sequence to that of human RBM3. In the testis of adult mice, Rbm3 mRNA and protein were detected in Sertoli cells, but not germ cells, of seminiferous tubules at all stages. The expression was not observed in Sertoli cells of fetuses, but was observed in newborn and older mice. In the TAMA26 mouse Sertoli cell line, the Rbm3 expression level was increased or decreased within 12 hours after temperature shift from 37 degrees C to 32 degrees C or 39 degrees C, respectively. In contrast to Cirp, the cold-induced growth suppression of TAMA26 cells was not affected by suppression of the Rbm3 expression. When mouse testis was exposed to heat stress by experimental cryptorchidism, the level of Rbm3 was decreased in Sertoli cells. Rbm3 may play important roles distinct from those played by Cirp in spermatogenesis and cryptorchidism by regulating the gene expression in Sertoli cells.     

无精子和严重少精子患者Y染色体AZF微缺失的PCR筛查

目的：探讨Y染色体上AZF微缺失与精子生成的遗传效应关系,建立对无精子症和严重少精子患者Y染色体微缺失的筛查方法。方法;本文应用聚合酶链反应（PCR）技术对无精子症和严重少精子患者进行Y染色体上AZFa,AZFb,AZFc等5个基因片段的微缺失检测。结果：在64例无精子患者中,AZFb,AZFc,RBM人率分别为4．69％、17．19％、4．69％、未发现AZFa缺失。在53例严重少精子患者中,除1例同时伴有RBM缺失外,均为AZFc缺失,未发现AZFa和AZFb缺失,缺失率为18．87％。30例正常对照组未发现5个区域缺失。结论：精子发生与Y染色体上的多个基因有关,AZFb,AZFc的微缺失是导致无精子和严重少精子的重要原因,AZFc区微缺失可作病因筛查主要候选基因。     

Developmental stage-specific expression of Rbm suggests its involvement in early phases of spermatogenesis

Rbm is a male infertility gene located on the Y chromosome that is expressed in the testis. To investigate the specific events of spermatogenesis in which Rbm plays a role, the precise pattern of expression of Rbm in the mouse testis was determined. An antibody was generated against the Rbm protein and used to detect a single specific band of 43 kDa in size in mouse testicular lysates. In situ hybridization, immunoblot and immunohistochemistry analyses together indicated that Rbm was expressed in spermatogonia, preleptotene spermatocytes, late leptotene to early pachytene spermatocytes but not in mid-pachytene spermatocytes or subsequent stages of differentiation, including haploid germ cells. These observations suggest that Rbm functions in early but not later stages of male germ cell development.     

The human autosomal gene DAZLA: testis specificity and a candidate for male infertility

The DAZ (Deleted in AZoospermia) and DAZLA (DAZ-like autosomal) genes may be determinants of male infertility. The DAZ gene on the long arm of the human Y chromosome is a strong candidate for the 'azoospermia factor' (AZF). Its role in spermatogenesis is supported by its exclusive expression in testis, its deletion in a high percentage of males with azoospermia or severe oligospermia, and its homology with a Drosophila male infertility gene boule. No DAZ homologous sequences have been found on the mouse Y chromosome. Instead, a Dazla gene was isolated from mouse chromosome 17 and has been considered to be a murine homologue of DAZ. However, the homology between human DAZ and mouse Dazla is not strong, and Dazla contains only one of the seven DAZ repeats found in DAZ. We report the isolation of the human DAZLA gene by screening a human testis cDNA library with a DAZ cDNA clone. DAZLA encodes only one DAZ repeat and shares high homology with the mouse Dazla, indicating that these two genes are homologues. Using a panel of rodent-human somatic cell lines and fluorescence in situ hybridization, the DAZLA gene was mapped to 3p24, a region not known to share homology with mouse chromosome 17. The DAZLA gene may be involved in some familial cases of autosomal recessive male infertility.      

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.     

人类Y染色体微缺失与精子生成障碍的研究进展

本文就人类Y染色体的结构及其与精子生成相关的主要功能基因的研究进展作了综述，重点对AZF区的USP9Y.RBM. DAZ. CDY等基因的缺失与精子生成障碍的关系进行了探讨。为临床实施辅助生育技术治疗前对精子质量的筛查.无精症患者的诊断及遗传咨询提供理论依据。     

Characterization of the genomic organization, localization and expression of four PRY genes (PRY1, PRY2, PRY3 and PRY4).

PRY (PTP-BL related on the Y chromosome) has been proposed as a candidate spermatogenesis gene. We report the characterization of the genomic structure, the number of copies on the Y chromosome and the expression of the gene. By comparison of the cDNA sequence with the genomic sequence, five exons were identified. Analysis of GenBank-derived clones on the Y chromosome revealed the presence of two full-length copies in azoospermia factor region b (AZFb) (PRY1 and PRY2) and two shorter versions of the PRY gene containing exons 3, 4 and 5 in AZFc (PRY3 and PRY4). A clone containing sequences homologous to exons 3, 4 and 5 is located in area 5L (between AZFa and AZFb), a clone containing a sequence homologous to exon 5 is located in area 5M (in AZFb) and a clone containing a fragment homologous to exon 3 is located in 6F. A repeat structure of exons 1 and 2 is present on the short arm of the Y chromosome as well as on the long arm. PRY1 and PRY2, two gene copies that are located in AZFb, a region often deleted in patients with severe male infertility, were shown to be expressed in the testis. PRY may therefore play an important role in spermatogenesis.     

A putative human male infertility gene DAZLA: genomic structure and methylation status

The DAZLA (DAZ Like Autosomal) gene on human chromosome 3 shares a high degree of homology with the DAZ (Deleted in AZoospermia) gene family on the Y chromosome, a gene family frequently deleted in males with azoospermia or severe oligospermia. The involvement of both DAZ and DAZLA in spermatogenesis is suggested by their testis-specific expression and their homology with a Drosophila male infertility gene, boule. Whereas male infertility resulting from deletion of the DAZ genes on the Y chromosome occurs sporadically, that due to a defective DAZLA gene is expected to be inheritable. The fraction of males with idiopathic azoospermia or oligospermia that harbour mutations in the DAZLA gene remains unknown. As a prerequisite for mutation screening, the genomic structure of the DAZLA gene was elucidated and found to consist of 11 exons spanning 19 kh. The exon/intron boundaries are conserved between DAZ and DAZLA. The 5' end of both genes are hypomethylated in spermatozoa but not in leukocytes or placenta, consistent with the expression pattern of the genes. The genomic structure of DAZLA paves the way for mutation detection in families with autosomal recessive male infertility.      

Combined cytogenetic and Y chromosome microdeletion screening in males undergoing intracytoplasmic sperm injection

We evaluated the frequency of chromosomal aberrations and microdeletions of the Y chromosome in a sample of 204 patients included in an intracytoplasmic sperm injection (ICSI) programme. The prevalence of Y chromosome deletions in males with severely or only moderately reduced sparm counts is mainly unknown, so that patients were chosen with sperm counts ranging from mild oligozoospermia to azoospermia. While six out of 158 (3.8%) patients showed constitutional chromosomal aberrations, only two out of 204 (0.98%) patients were diagnosed with a microdeletion of Yq11. One had a terminal deletion in subinterval 6 of Yq11.23 which included the DAZ gene and a corresponding sperm count < 0.1 x 10(6) spermatozoa/ml. The second patient had an isolated deletion of marker Y6PH54c, a more proximal site in subinterval 5 on Yq11.23, but repeatedly showed sperm counts of 3-8 x 10(8) spermatozoa/ml. Thus, of the 158 patients who underwent a combined cytogenetic and Y- microdeletion screening, eight patients (5.1%) showed chromosomal abnormalities, either at the cytogenatic (n = 6) or the molecular level (n = 2). In conclusion, although rare in number, microdeletions of the Y chromosome can also be observed in patients with moderately reduced sperm counts. A more proximal site of the deletion breakpoint does not necessarily imply a more severe impairment of spermatogenesis than a distal deletion site. In our sample, the overall frequency of constitutional chromosomal aberrations exceeded the incidence of microdeletions of the Y chromosome even in patients with idiopathic azoo- or severe oligozoospermia.      

T-STAR/ETOILE: a novel relative of SAM68 that interacts with an RNA-binding protein implicated in spermatogenesis.

RBM is an RNA-binding protein encoded on the Y chromosome in mammals and is expressed only in the nuclei of male germ cells. Genetic evidence from infertile men implicates it in spermatogenesis, but its function is unknown. Of a number of potential partners for RBM identified by a yeast two-hybrid screen with testis cDNA, the most frequent isolates encoded a novel RNA-binding protein, termed T-STAR, that is closely related to SAM68, an Src-associated protein of unknown function. The mouse homologue was also cloned and designated étoile. It mapped to chromosome 15, while T-STAR mapped to the syntenic region on human chromosome 8. T-STAR/étoile is expressed primarily in the testis; in rat germ cells, the expression of both T-STAR/étoile and SAM68 is regulated during meiosis. Transfection of T-STAR/étoile fused with green fluorescent protein into HeLa cells caused an accumulation of protein in a novel compartment of the nucleus, adjacent to the nucleolus but distinct from the peri-nucleolar compartment. RBM and other hnRNP G family members are candidate downstream targets for regulation by T-STAR/ETOILE and SAM68.     

Clustering of Y chromosome deletions in subinterval E of interval 6 supports the existence of an oligozoospermia critical region outside the DAZ gene.

Y chromosome molecular analysis was performed using the STS-PCR technique in 50 patients with oligozoospermia. Microdeletions of interval 6 of the Y chromosome were detected in seven patients, in six of whom subinterval E was affected. All patients retained the RBM1 and DAZ genes, while in one deletion involved the SPGY gene. The size of the deletion was not apparently related to the severity of the disease. These results suggest the presence of an oligozoospermia critical region on the Y chromosome within subinterval E of interval 6.     

High-resolution fluorescence in situ hybridization of human Y-linked genes on released chromatin

Genes within the differential region of the human Y chromosome do not recombine, and therefore the determination of their location depends on physical mapping. Yeast artificial chromosome (YAC) contigs spanning the euchromatic region of the human Y have become a powerful tool for the generation of an overlapping clone map. With this approach,however, complete physical mapping is difficult in Y euchromatic regions that are rich in repetitive sequences. We have, therefore, made use of the fluorescence in situ hybridization technique as an alternative strategy for physically mapping the PRKY and AMELY genes as well as the TSPY, RBM and DAZ gene families to human Y chromosomes in prometaphase and to extended Y chromatin in interphase. From our results, the following order of gene sequences in interval 3 of the short arm of the human Y chromosome is suggested: TSPY major with few RBM sequences interspersed-PRKY-AMELY-TSPY minor with few RBM sequences interspersed-cen. On the long arm, RBM sequences appear to be distributed over wide regions of intervals 5 and 6 with few TSPY sequences interspersed. Distal to an RBM signal cluster, a large cluster of DAZ signals is located with only a few DAZ and RBM signals overlapping in between the two clusters. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of a Y chromosome haplogroup associated with reduced sperm counts

In man, infertility is associated with microdeletions of specific regions of the long arm of the Y chromosome. This indicates that factors encoded by the Y chromosome are necessary for spermatogenesis. However, the majority of men with either idiopathic azoospermia or oligozoospermia have grossly intact Y chromosomes and the underlying causes of their infertility are unknown. We hypothesized that some of these individuals may carry other rearrangements or sequence variants on the non-recombining region of the Y chromosome that may be associated with reduced spermatogenesis. To test this hypothesis, we typed the Y chromosome in a group of Danish men with known sperm counts and compared the haplotype distribution with that of a group of unselected Danish males. We found that one class of Y chromosome, referred to as haplogroup 26+, was significantly overrepresented (27.9%; P < 0.001) in the group of men with either idiopathic oligozoospermia (defined as <20 x 10(6 )sperm/ml) or azoospermia compared to the control Danish male population (4.6%). This study defines, for the first time, a class of Y chromosome that is at risk for infertility in a European population. This observation suggests that selection may be indeed active on the Y chromosome, at least in the Danish population, raising the possibility that it could alter the pattern of Y chromosome haplotype distribution in the general population.     

Y chromosome microdeletions, in azoospermic or near-azoospermic subjects, are located in the AZFc (DAZ) subregion

Submicroscopic deletions of the Y chromosome and polymorphisms of the androgen receptor (AR) gene in the X chromosome have been observed in men with defective spermatogenesis. To further define the subregions/genes in the Y chromosome causing male infertility and its relationship to polymorphisms of the AR polyglutamine tract, we screened the genomic DNA of 202 subfertile males and 101 healthy fertile controls of predominantly Chinese ethnic origin. Y microdeletions were examined with 16 sequence-tagged site (STS) probes, including the RBM and DAZ genes, spanning the AZFb and AZFc subregions of Yq11, and related to the size of trinucleotide repeat encoding the AR polyglutamine tract. Y microdeletions were detected and confirmed in three out of 44 (6.8%) of azoospermic and three out of 86 (3.5%) severely oligozoospermic patients. No deletions were detected in any of the patients with sperm counts of >0.5 x 10(6)/ml, nor in any of the 101 fertile controls. All six affected patients had almost contiguous Y microdeletions spanning the entire AZFc region including the DAZ gene. The AZFb region, containing the RBM1 gene, was intact in five of the six subjects. Y deletions were not found in those with long AR polyglutamine tracts. Our study, the first in a Chinese population, suggest a cause and effect relationship between Y microdeletions in the AZFc region (possibly DAZ), and azoospermia or near-azoospermia. Y microdeletions and long AR polyglutamine tracts appear to be independent contributors to male infertility.      

Dicentric chromosome Y associated with Leydig cell agenesis and sex reversal

The nature of a non-mosaic marker Y chromosome observed in a pseudohermaphrodite patient with Leydig cell agenesis was investigated by high-resolution chromosome analysis and molecular probes from the Y chromosome. Cytogenetically, the marker chromosome appeared to be an isodicentric, with breakage in Yq11.21. Double copies of all Yp-specific loci tested, including SRY, were present. The most distal Yq portion detected in patient DNA was DXS278-C, which maps to interval D in the chromosome Yq deletion map. Fragment DXS278-B, which maps to deletion interval E, was absent. The possible relationship between this cytogenetic abnormality and Leydig cell agenesis, a finding never reported in association with Y chromosome rearrangements, is discussed.     

Characterization of genes encoding translation initiation factor eIF- 2gamma in mouse and human: sex chromosome localization, escape from X- inactivation and evolution

The Delta Sxrb interval of the mouse Y chromosome is critical for spermatogenesis and expression of the male-specific minor transplantation antigen H-Y. Several genes have been mapped to this interval and each has a homologue on the X chromosome. Four, Zfy1 , Zfy2 , Ube1y and Dffry , are expressed specifically in the testis and their X homologues are not transcribed from the inactive X chromosome. A further two, Smcy and Uty , are ubiquitously expressed and their X homologues escape X-inactivation. Here we report the identification of another gene from this region of the mouse Y chromosome. It encodes the highly conserved eukaryotic translation initiation factor eIF-2gamma. In the mouse this gene is ubiquitously expressed, has an X chromosome homologue which maps close to Dmd and escapes X-inactivation. The coding regions of the X and Y genes show 86% nucleotide identity and encode putative products with 98% amino acid identity. In humans, the eIF-2gamma structural gene is located on the X chromosome at Xp21 and this also escapes X-inactivation. However, there is no evidence of a Y copy of this gene in humans. We have identified autosomal retroposons of eIF-2gamma in both humans and mice and an additional retroposon on the X chromosome in some mouse strains. Ark blot analysis of eutherian and metatherian genomic DNA indicates that X-Y homologues are present in all species tested except simian primates and kangaroo and that retroposons are common to a wide range of mammals. These results shed light on the evolution of X-Y homologous genes.