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.      

特发性无精子症及少弱精子症患者Y染色体AZF微缺失筛查分析

目的探讨特发性无精子症及少弱精子症不育男性与Y染色体AZF微缺失的关系.方法用双重PCR技术对63例患者(无精于症41例,少弱精子症14例,严重少精子症8例)进行Y染色体AZFa、AZFb、AZFc、SRY的微缺失筛查.同时对26例无精于症患者行睾丸活检、组织学评估.结果63例中AZF微缺失7例,缺失率为11.1%.其中无精子症5例,严重少精子症2例.AZFc缺失4例,AZFb缺失2例,AZFb AZFc缺失1例,未发现AZFa区缺失.63例及对照组30例SRY基因扩增均阳性.26例无精子症患者行睾丸活检、组织学检查,无1例精子发生正常.结论Y染色体微缺失,特别是AZFc区DAZ基因的微缺失,是引起无精子和严重少弱精子等生精障碍而致男性不育较为重要的遗传学因素.     

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.      

Deletion of RBM and DAZ in azoospermia: evaluation by PRINS.

Molecular and cytogenetic studies from infertile men have shown that one or more genes controlling spermatogenesis are located in proximal Yq11.2 in interval 6 of the Y chromosome. Microdeletions within the azoospermia factor region (AZF) are often associated with azoospermia and severe oligospermia in men with idiopathic infertility. We evaluated cells from a normal-appearing 27-year-old man with infertility and initial karyotype of 45,der(X)t(X;Y)(p22.3;p11.2)[8]/46,t(X;Y)(p22.3;p11.2)[12]. By fluorescence in situ hybridization with dual-color whole chromosome paint probes for X and Y chromosomes, we confirmed the Xp-Yp interchange. By primed in situ labeling, we identified translocation of the SRY gene from its original location on Yp to the patient's X chromosome at band Xp22. We also obtained evidence that the apparent marker was a der(Y) (possibly a ring) containing X and Y domains, and observed that the patient's genome was deleted for RBM and DAZ, two candidate genes for AZF.     

精子发生障碍患者Y染色体微缺失的研究

目的研究无精子症和少精子症患者Y染色体上无精子症因子(azoospermicfactor,AZF)微缺失情况,建立Y染色体微缺失的分子诊断的临床筛查方法,分析原发性无精子症和少精子症患者与Y染色体微缺失的关系。方法采用多重PCR、凝胶电泳技术对56例无精子症和少精子症患者的10个STS位点或基因进行检测与筛查。结果20例精子密度正常的生育男性未检测出Y染色体微缺失;56例无精子症和少精子症患者中有9例有AZF区域的微缺失,总缺失率16.1%(9/56),AZFc/DAZ区发生微缺失频率较高。结论Y染色体微缺失是导致男性不育患者精子发生障碍的重要原因之一,AZF侯选基因在精子发生过程中可能起重要作用。     

呼和浩特地区209例无精子症和严重少弱精子症患者的遗传因素调查

目的探讨染色体数目和结构异常,以及Y染色体无精子因子基因拷贝缺失与男性不育的关系。方法利用染色体G显带和PCR检测技术,对209例无精症和少弱精症患者进行外周血染色体检查,对在染色体核型分析中Y染色体部分缺失患者5例,11例小Y患者,以及1例Y染色体数目和结构均有异常的嵌合体患者,共17例进行Y染色体微缺失检测。结果共发现染色体异常核型71例,占34.9%。Y染色体微缺失患者4例。结论在无精症和少弱精症患者中存在较高频率染色体数目和结构异常,以及无精子因子基因拷贝缺失,遗传因素是造成男性不育的重要因素。     

男性不育患者Y染色体AZF基因微缺失检测

目的探讨原发性无精子症、严重少精子症及少精子症患者与Y染色体无精子因子（azoospermia factor,AZF）区微缺失的关系。方法采用多重PCR方法对对照组192例已正常生育男性和实验组448例男性不育患者进行AZF区域内的15个序列标签位点（STS）的检测。结果对照组未发现AZF基因微缺失,实验组448例患者检测出五种AZF微缺失类型共41例,总缺失率为9.2%（41/448）,其中无精子症、严重少精子症和少精子症患者的缺失率分别为12.0%（19/158）、10.8%（17/157）、3.8%（5/133）,无精子症和严重少精子症患者Y染色体AZF微缺失率明显高于少精子症组,差别有统计学意义（P〈0.05）。使用15个STS位点进行检测其检出率较利用欧洲男科学会（European Academy of Andrology,EAA）推荐的6个STS位点提高约14%（5/36）。结论AZF微缺失是引起原发性无精子症、严重少精子症和少精子症的重要原因之一;增加STS位点检测数有利于提高AZF微缺失的检出率。     

Absence of DAZ gene mutations in cases of non-obstructed azoospermia

Sequenced-tagged site (STS) analysis of the Y chromosome long arm (Yq) of azoospermic males has identified a minimum common deleted region of several hundred kilobases in approximately 13% of cases. A candidate azoospermia gene, DAZ (deleted in azoospermia), has been isolated from this region. DAZ has also been shown to be absent in severely oligozoospermic males albeit at a much lower frequency. These data, although highly suggestive, do not constitute formal proof that DAZ actually plays a role in azoospermia, as no small intragenic deletions, rearrangements or point mutations in the gene have been found. In this study we report the screening of DNA from 168 azoospermic/oligospermic males for the presence of the DAZ gene. Deletions involving DAZ were detected in five out of 43 (11.6%) azoospermic males whereas none were found in the remaining 125 oligospermic patients. We present the genomic structure of the 5' end of the DAZ gene together with its sequence analysis in 30 non-obstructed azoospermic males. No mutations in DAZ were found in any of the patients sequenced. These data provide no formal proof that DAZ is AZF. Thus the possibility is still valid that another gene(s) mapping to the deletion interval may be responsible for, or contribute to, the observed phenotypes. Alternatively, if DAZ is AZF, they suggest that the most frequent cause of gene inactivation is via large deletions possibly mobilized by Y chromosome repetitive sequences.      

810例严重少(无)精子症患者Y染色体微缺失筛查与分析

目的筛查原发无精子症与重度少精子症患者Y染色体微缺失情况,探讨Y染色体微缺失与男性不育的关系。方法采用改良多重PCR方法对810例男性不育患者(457例原发无精子症和353例严重少精子症)基因组DNA进行Y染色体微缺失筛查。结果810例患者中发现77例Y染色体微缺失患者,缺失率为9.5%,其中少精子症31例,均为AZFc微缺失,无精子症46例,缺失类型呈多样化。缺失类型包括AZFa微缺失3例(3.90%),AZFb微缺失2例(2.60%),AZFc微缺失63例(81.82%),AZFb+c微缺失4例(5.19%),AZFa+b+c微缺失5例(6.49%)。结论Y染色体微缺失是原发无精子症和少精子症的重要原因之一,AZFc缺失为最常见的缺失类型,对此类患者进行Y染色体微缺失的常规筛查是有必要的,尤其是拟行辅助生殖技术助孕的不育患者。     

Partial rescue of the Dazl knockout mouse by the human DAZL gene

Y-chromosomal DAZ (deleted in azoospermia) and autosomal DAZ-like (DAZL) comprise a gene family involved in gametogenesis. Y-chromosomal and autosomal genes only co-exist in humans and old world monkeys, indicating that DAZ genes are a recent acquisition of the Y chromosome. In most mammals, the ancestral Dazl alone is sufficient to complete gametogenesis. It is not yet understood why humans and old world monkeys have a second set of genes that are apparently necessary for spermatogenesis, since deletions removing the Y-chromosomal DAZ are often associated with azoo- or oligospermia. We used transgenic mice carrying either human DAZL or human DAZ on a mouse Dazl null background to investigate the functions of the human homologues. Both transgenes enabled prophase spermatocytes to be produced, mainly of the leptonema/zygonema stage, but failed to promote differentiation into mid- to late pachytenes. The presence of human DAZL resulted in a larger amount of early germ cells compared with that observed in DAZ. The degree of rescue was independent of copy number, integration site or presence of the DAZ repeat region for the DAZ transgenes. These findings confirm that DAZL and DAZ can only substitute for early functions of the murine homologue resulting in the establishment of the germ cell population and partial progression into meiosis.     

Microdeletions of a Y-specific marker,Yfm1, and implications for a role in spermatogenesis

We have detected deletions of a Y-specific microsatellite marker, Yfm1, located on the Y chromosome (Yq) within interval 6 and near the DAZ (deleted in azoospermia) genes, in 9/89 oligospermic and 17/68 azoospermic Japanese men. No Yfm1 deletions were detected in the 150 normal fertile males examined as controls. Yfm1 deletions in the oligo- and azoospermic males were associated with other deletions that removed entire DAZ genes in those infertile men. These deletions indicated that all Yfm1 loci are located within azoospermia factor c (AZFc) in interval 6 on the long arm of the Y chromosome. Mapping Yfm1 on the Y chromosome using the draft sequence of the human genome revealed that at least three Yfm1 loci are located within about 25–30 kbp of the DAZ genes. Moreover, the Yfm1 marker showed the least number of copies in Japanese males derived from a Y chromosomal lineage called haplotype II, defined by having the Y Alu polymorphism (YAP) insertion. Males from this haplotype II lineage are known from our previous studies to have lower spermatogenic abilities, with higher rates of oligo- and azoospermia than other haplotypes. The least number of Yfm1 loci, whose copy number may correspond to that of the DAZ genes, may be a risk factor predisposing an individual to azoospermia or oligospermia. Received: October 26, 2001 / Accepted: February 12, 2002     

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.     

Genetic risk factors in infertile men with severe oligozoospermia and azoospermia.

BACKGROUND: Male infertility due to severe oligozoospermia and azoospermia has been associated with a number of genetic risk factors. METHODS: In this study 150 men from couples requesting ICSI were investigated for genetic abnormalities, such as constitutive chromosome abnormalities, microdeletions of the Y chromosome (AZF region) and mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. RESULTS: Genetic analysis identified 16/150 (10.6%) abnormal karyotypes, 8/150 (5.3%) AZFc deletions and 14/150 (9.3%) CFTR gene mutations. An abnormal karyotype was found both in men with oligozoospermia and azoospermia: 9 men had a sex-chromosomal aneuploidy, 6 translocations were identified and one marker chromosome was found. Y chromosomal microdeletions were mainly associated with male infertility, due to testicular insufficiency. All deletions identified comprised the AZFc region, containing the Deleted in Azoospermia (DAZ) gene. CFTR gene mutations were commonly seen in men with congenital absence of the vas deferens, but also in 16% of men with azoospermia without any apparent abnormality of the vas deferens. CONCLUSIONS: A genetic abnormality was identified in 36/150 (24%) men with extreme oligozoospermia and azoospermia. Application of ICSI in these couples can result in offspring with an enhanced risk of unbalanced chromosome complement, male infertility due to the transmission of a Y-chromosomal microdeletion, and cystic fibrosis if both partners are CFTR gene mutation carriers. Genetic testing and counselling is clearly indicated for these couples before ICSI is considered.     

无精子和少精子症患者Y染色体精子发生相关基因检测分析

目的探讨原因不明无精子症和少精子症患者与Y染色体精子发生相关基因的关系.方法对82例原因不明的无精子症和少精子症患者进行G带染色体核型分析,筛选核型正常无精子症和少精子症患者,采用多重PCR技术对Y染色体上AZF区15个序列标记位点进行检测.结果染色体核型异常16例,异常发生率为19.5%;66例核型正常无精子症和少精子症患者,有7例在Y染色体上出现不同位点基因片段微缺失,缺失率为10.6%.结论Y染色体上基因片段微缺失是造成无精子或少精子的重要原因之一,采用多重PCR技术对原因不明的无精子症和少精子症患者Y染色体精子发生相关基因进行检测分析是一种有效的好方法.     

Associations of Y-chromosome subdeletion gr/gr with the prevalence of Y-chromosome haplogroups in infertile patients

Microdeletions in azoospermia factor (AZF) region on distal Yq are associated with male infertility and spermatogenic failure due to intra-chromosomal homologous recombination between large nearly identical repeat amplicons and are found in ∼10% of azoospermic and severe oligozoospermic cases. Although AZFc is deleted in azoospermia or oligozoospermia, no definitive conclusion has been drawn for the role of partial AZFc deletions to spermatogenic failure. Therefore, this study is planned to investigate the role of gr/gr subdeletions in individuals with spermatogenic failure and to find its relationship with Y chromosome haplogroups (HGs) in infertile men from Indian population. It is a case-control study involving 236 azoospermic, 182 oligospermic and 240 healthy normozoospermic men. We found 18 gr/gr, 11 b1/b3 and 2 b2/b3 subdeletions in azoospermic patients and 12 gr/gr, 5 b1/b3 and 4 b2/b3 subdeletions in oligospermic patients. However, we also found seven gr/gr deletions in normozoospermic men. Seven patients each with spermatogenic arrest and oligospermia who carry gr/gr subdeletions have deleted DAZ3/DAZ4 genes. A total of 11 patients with sertoli cell-only syndrome (SCOS) and 5 oligospermic patients with gr/gr subdeletions also have DAZ1/DAZ2 genes deleted indicating that deletions of DAZ genes contributed differently to damage to spermatogenic process. L1 HG is found in patients showing b1/b3 subdeletions, whereas HG H1a2 and H1b were found in normozoospermic individuals with gr/gr subdeletions. Our results provide evidence of association between the occurrence of subdeletions and male infertility as well as the severity of the spermatogenic failure.     

Genetics of functional and structural defects in spermatogenesis

The genetic reasons for male infertility are still poorly understood. In approximately 30 % of infertile men no reason for their defect in spermatogenesis can be found (idiopathic infertility). In a high percentage of these patients single gene defects are assumed to be responsible for the infertility. Well-known reasons for infertility are microdeletions on the long arm of the Y chromosome. In approximately 3–18 % of patients with azoospermia or severe oligospermia these deletions can be detected by using molecular techniques. In 4–6 % of infertile men chromosomal abnormalities are responsible for their andrological disorder. While numeric aberrations are widely observed in patients with azoospermia, alterations in chromosomal structure are prominent in patients with oligozoospermia. Chromosomal anomalies can be found only in rare cases of patients with structural or functional sperm defects. Up to now the genetic basis has only be described for a few functional or structural sperm defects (immotile cilia syndrome, globozoospermia). More recently, it became possible to identify genes involved in spermatogenesis and to investigate their functions in male germ cell differentiation by using new tools of molecular biology, e. g. gene replacement techniques in the mouse. For the majority of these genes homologous human genes are known. However, the role of these genes in human spermatogenesis and their relevance for male fertility have still to be elucidated.     

特发性无精子症和严重少精子症患者DAZ基因缺失的分析

目的　评估特发性无精子症和严重少精子症患者Y染色体上DAZ基因缺失的发生情况。方法　采用聚合酶链反应技术 (PCR)扩增 33例特发性无精子症和严重少精子症患者DAZ基因中的 4个序列标记位点SY15 4、SY2 5 4、SY2 5 5和SY15 5。 5 0例生育男性为阳性对照组 ,5例女性为阴性对照组。结果　 33例特发性无精子症和严重少精子症患者DAZ基因缺失率为 15 2 % ,其中 2 6例特发性无精子症患者有 4例缺失 (15 4 % ) ,1例染色体核型为 4 7,XXY ;7例特发性严重少精子症患者中有 1例缺失 (14 3% )。 4个序列标记位点在阳性对照组中均有条带扩增 ,在阴性对照组中未见条带扩增。结论　特发性无精子症和严重少精子症患者均存在DAZ基因缺失 ,特发性无精子症患者缺失率高于特发性严重少精子症患者 ,与国外报道相一致。聚合酶链反应扩增DAZ基因位点是筛选Y染色体缺失的有效方法。     

男性不育患者的细胞遗传学分析

目的对男性不育患者进行染色体核型的检测,以指导其生育。方法1．应用规范的WHO精液检查方法检查男性不育患者精液标本。2．应用细胞遗传学检测男性不育患者外周血染色体核型分析。结果1．精液检查结果：男性不育组患者356例,包括无精子症82例、严重少精子症126例、少弱精子症148例,精液正常、核型正常男性组对照50例。2．细胞染色体检查：356例男性不育患者全部进行外周血淋巴细胞染色体核型分析,发现55例染色体核型异常,包括性染色体异常24例,常染色体异常21例和染色体多态性10例。其中,无精子症组的染色体异常率25．61％（21／81）,严重少精子症患者染色体核型异常率为11．90％（15／126）,少弱精子症患者染色体核型异常率为12．84％（19／148）。结论男性不育患者核型异常率为15．45％,远高于正常人群发病率。细胞遗传学染色体检查对男性不育的生育指导有重要意义。无精子症患者进行染色体检查尤其必要。