This web only provides the extract of this article. If you want to read the figures and tables, please reference the PDF full text on Blackwell Synergy. Thank you.

- .Original Article . -

Uniform deletion junctions of complete azoospermia factor region c deletion in infertile men in Taiwan

Chao-Chin Hsu¹,Pao-Lin Kuo², Louise Chuang², Ying-Hung Lin³, Yen-NiTeng⁴, Yung-Ming Lin⁵

¹Department of Obstetrics & Gynecology, China Medical University, Taichung 400, Taiwan, China

²Department of Obstetrics & Gynecology, National Cheng Kung University, College of Medicine, Tainan 704, Taiwan, China

³The Institute of Basic Medical Science, National Cheng Kung University, College of Medicine, Tainan 704, Taiwan, China

⁴Department of Early Childhood Education and Nursery, Chia Nan University of Pharmacy and Science, Tainan 717, Taiwan, China

⁵Department of Urology, National Cheng Kung University, College of Medicine, Tainan 704, Taiwan, China

Abstract

Aim:To determine the deletion junctions of infertile men in Taiwan with azoospermia factor region c (AZFc) deletions and to evaluate the genotype/phenotype correlation. Methods: Genomic DNAs from 460 infertile men were examined. Bacterial artificial chromosome clones were used to verify the accuracy of polymerase chain reaction. Deletion junctions of the AZFc region were determined by analysis of sequence-tagged sites and gene-specific markers. Results: Complete AZFc deletions, including BPY2, CDY1 and DAZ genes, were identified in 24 men. The proximal breakpoints were clustered between sY1197 and sY1192, and the distal breakpoints were clustered between sY1054 and sY1125 in all but one of the 24 men. The testicular phenotypes of men with complete AZFc deletion varied from oligozoospermia, to hypospermatogenesis, to maturation arrest. Conclusion: We identified a group of infertile men with uniform deletion junctions of AZFc in the Taiwan population. Despite this homogeneous genetic defect in the AZFc region, no clear genotype/phenotype correlation could be demonstrated. (Asian J Androl 2006 Mar; 8: 205-211)

Keywords: azoospermia factor; BPY2; CDY1; deleted in azoospermia; Y chromosome

Dr Yung-Ming Lin, M.D., Department of Urology, National Cheng Kung University Medical College and Hospital, 138 Sheng-Li Road, Tainan 704, Taiwan, China.

Tel: +886-6276-6179, Fax: +886-6238-3678
E-mail: linym@mail.ncku.edu.tw
Received 2005-05-17 Accepted 2005-11-08

1 Introduction

Deletions in the azoospermia factor (AZF) region on the Y chromosome have been considered one of the major genetic causes of male infertility. Based on observations of recurrent, non-overlapping deletion patterns, it was proposed that multiple genes might be implicated in spermatogenesis defects. These genes are located in the proximal, middle and distal subregions of Yq11, designated AZFa, AZFb and AZFc, respectively [1]. Among the three non-overlapping AZF loci, deletions occur most commonly in AZFc. AZFc deletion accounts for 10-15% of men with non-obstructive azoospermia and 5-10% of those with oligozoospermia [1-6].

Recently, several deletion mechanisms have been proposed in these AZF regions [7-11]. The deletion in the AZFa region is believed to be the result of recombination between homologous retroviral sequence blocks, HERV15yq1 and HERV15yq2, leading to the deletions of both USP9Y and DBY genes [9]. For the deletions involving the AZFb+c regions, three types of deletion models have been identified: palindrome P5 to the proximal arm of palindrome P1; palindrome P5 to the distal arm of palindrome P1; and palindrome P4 to the distal arm of palindrome P1 [10, 11]. For the AZFc region, a more detailed physical map has been constructed by Kuroda-Kawaguchi et al. [7]. By sequencing highly overlapping bacterial artificial chromosome (BAC) clones derived from a single man, the regional structure and repetitive sequence composition spanning the entire AZFc were determined. They found that AZFc of the Y chromosome is made up almost entirely of long direct and inverted repeats, or amplicons, and is particularly susceptible to deletions. Homologous recombination between amplicons b2 and b4 is probably the most common cause of AZFc deletion [7]. It is noteworthy that partial AZFc deletion might cause spermatogenic failure, and several types of partial AZFc deletions have been proposed and designed as gr/gr, g1/g2, b1/b3 , b2/b3, rg/gr, g1/g3 and b3/b4 deletions [12, 13]. The gr/gr, g1/g2 and b1/b3 deletions, which remove deleted in azoospermia 1 (DAZ1) and deleted in azoospermia 2 (DAZ2) copies, were associated with varied degrees of spermatogenic impairment [12, 13].

Despite the highly polymorphic nature of this Y-chromosomal region, the AZFc deletion model suggested by Kuroda-Kawaguchi et al. [7] was based on DNA sequences of a single man. Although the polymorphic nature of the Y chromosome could be obviated by using genomic DNA from one man, the versatility of the proposed model should be tested in a different group. Given that AZFc deletion is one of the important genetic causes for male infertility, the determination of deletion junctions of the AZFc region in those patients would be of considerable value. Here, we collated the Y chromosome sequence-based map and designed gene-specific primers for deletion mapping analysis. Our goal was to define the extent of AZFc deletions in men in Taiwan with spermatogenic failure, and to address the genotype/phenotype correlation in men with AZFc deletion.

2 Materials and methods

2.1 Patients

From January 1997 to March 2004, DNA samples of 460 infertile men in Taiwan with oligozoospermia or non-obstructive azoospermia were collected for the study of genetic defects. Non-obstructive azoospermia was defined as spermatogenic defects on testicular biopsy or elevated serum follicle stimulating hormone (FSH) level, total testicular volume less than 30 mL, and no other applicable diagnosis. All infertile men underwent a comprehensive examination, including a detail history, physical examination, at least two consecutive semen analyses, endocrinology profiles (FSH, luteinizing hormone [LH], prolactin and testosterone), and chromosome analysis. This study had been approved by the National Scientific Council of Taiwan and the Institutional Review Board of National Cheng Kung University Medical Center. The study was designed in accordance with the Helsinki Declaration of 1975 on human experimentation. Informed consent was obtained from all enrollees.

2.2 Validation of DAZ-, BPY2- and CDY1-specific primers and polymerase chain reaction (PCR)

We designed a set of gene-specific primers for CDY1. The primers for DAZ and BPY2 were the same as described elsewhere [5]. In order to verify the specificity of these primers, five BAC clones were used that contained a single copy of the DAZ (RP11-26D12), CDY1 (RP11-497C14), CDY2 (RP11-509B6), BPY1 (RP11-264A13) or BPY2 (RP11-86G22) genes. The clones were available from Pieter de Jong’s BACPAC Resources Center (http://www.chori.org/bacpac). Genomic DNA and clone DNA were extracted using the standard methods. During PCR analysis, the sex-determining region Y (SRY) gene was used as an internal control for amplification failure. Each PCR reaction consisted of 0.12-0.50Mmol/L of primer, 1×PCR buffer, 1.5Mmol/LMgCl₂, 200Mmol/L of each deoxyribonucleotide triphosphate, 150ng of genomic DNA, and two units of Taq DNA polymerase (Perkin-Elmer Cetus, Emeryville, CA, USA) in a total volume of 20ML. Thermocycling (OmniGene Thermal Cycler; Hybaid, Ashford, Middlesex, UK) consisted of 10 min at 95°C for initial denaturation, followed by 30 cycles of denaturation at 94°C for 1 min, annealing at 62°C for 1 min, extension at 72°C for 1 min, and a final extension at 72°C for 10 min. The reaction products were fractionated on 2.5% agarose gels. The PCR products were made visible with ethidium bromide. For each assay, we incorporated the following controls: a genomic DNA sample from a normal fertile man; a genomic DNA sample from a normal fertile woman; a PCR mixture containing no DNA (blank control); and clone DNA. PCR amplification failures for these genes were further confirmed by at least two more amplification failures.

2.3 Determination of AZFc deletion junctions

According to the model proposed by Kuroda-Kawaguchi et al. [7], the proximal boundary of AZFc falls between sites sY1197 and sY1192, and the distal boundary of AZFc falls between sites sY1054 and sY1125. To determine the deletion junction, sY1197, sY1192, sY1054, and sY1125 were used. Site sY1196 is a marker proximal to sY1197, site sY1190 is a marker within AZFc, and site sY1201 is a marker distal to sY1125. The latter three markers were used for further confirmation of deletion junctions. The sequences of sequence-tagged site (STS) primers were retrieved from GenBank (http://www.ncbi.nlm.nih.gov/Genbank/). The primer sequences and sizes of the amplified fragments are listed in Table 1. We analyzed the deletion junctions of AZFc in patients with interstitial AZFc deletion, which was defined as deletion of one of BPY2, CDY1 or DAZ genes, or a combined deletion of at least two of these genes. The PCR conditions for STS markers were the same as those for gene-specific markers. Cases with AZFc deletion were also analyzed for the presence of sY159 and sY160 to exclude the possibility of Yq terminal deletion according to methods described previously [5].

3 Results

3.1 Validation of gene-specific primers

The specificity of primers for BPY2, DAZ and CDY1 is demonstrated in Figure 1. Sites sY277 and sY283 were specific to the DAZ gene. By using both primers, DAZ could be amplified in a DAZ-containing clone and genomic DNA from normal men, but not in genomic DNA from female subjects. BPY2 primer amplified a single band from a BPY2-containing clone and genomic DNA from normal men, but could not amplify a BPY1-containing clone, genomic DNA from female subjects. Similarly, CDY1 primer amplified a single band from a CDY1-contaning clone, genomic DNA from normal men, but could not amplify a CDY2-containing clone, genomic DNA from female subjects.

3.2 Uniform AZFc deletions and genotype/phenotype correlation

In this study, we identified 24 men with interstitial AZFc deletion. All of these men had a normal male karyotype. The deletion statuses of 24 men and their corresponding testicular phenotypes are shown in Figure 2. Twenty-three men revealed proximal breakpoints between sY1197 and sY1192 and a distal breakpoint between sY1054 and sY1125. Their testicular phenotypes were oligozoospermia in 11 men and azoospermia in 12 men. The sperm counts for the 11 oligozoospermic men varied from 8.8×10⁶/mL to lower than 0.1×10⁶/mL. Of the 12 men with azoospermia, eight underwent testicular biopsy. Their histologies were hypospermatogenesis in five men and maturation arrest in three men. Testicular histology was not available in the remaining four men. Patient TW158 revealed proximal breakpoints between sY1197 and sY1192 and distal breakpoints between CDY1 and sY1054. His testicular phenotype was oligozoospermia with a sperm count of 2× 10⁶/mL. All 24 men had completely lost the Y-chromosomal BPY2, DAZ and CDY1 genes.

3.3 De novo AZFc deletion

The 24 men were routinely asked to assist in obtaining blood samples from their male relatives in order to determine the origin of genetic defects. The fathers or brothers of six of the 24 men provided their blood samples for PCR analysis. All of them had intact Y chromosome, indicating that these deletions had arisen de novo.

4 Discussion

Deletions of the AZFc region are the most common known cause of spermatogenic defect. Kuroda-Kawaguchi et al. [7] presented strong evidences that most AZFc deletions involve a 3.5Mb segment, bounded by two 229kb direct repeats. It was hypothesized that recurrent deletion of the AZFc region was caused by recombination between two direct repeats, b2 and b4, flanking the AZFc region. By examining the deletion boundaries of 48 infertile men with AZFc deletion, they found identical deletion junctions in 47 cases [7]. In the present study, we also identified a group of infertile men in Taiwan with uniform recurrent AZFc deletion. The proximal breakpoints were clustered between sY1197 and sY1192, and the distal breakpoints clustered between sY1054 and sY1125 in all but one of the 24 men. Both the proximal and distal breakpoints are identical to those described by Kuroda-Kawaguchi et al. [7]. The different distal breakpoint in patient TW158 may be due to simple nucleotide polymorphism; however, we were unable to perform sequence analysis because there was insufficient DNA from this patient.

There have been debates on the various types of AZFc deletions [5, 7, 14]. It is proposed that seven gene families, including BPY2, DAZ, CDY1, CSPG4LY, GOLGA2LY, TTTY3 and TTTY4, are transcribed in the testis and located exclusively within the AZFc region [7]. According to this model, these gene families will be removed en block by a complete AZFc deletion [7]. However, Ferlin et al. [14] reported that some AZFc-deleted cases still retained the CDY1 gene. In our previous report of 12 men with DAZ deletions, four had complete deletions of the DAZ gene cluster but at least one copy of the other two genes in the AZFc region (BPY2 or CDY1) were retained [5]. With the new PCR protocol, BPY2, DAZ and CDY1 genes were absent in all men with complete AZFc deletion, including the 12 men described in our previous report. Therefore, the four men with isolated deletion of the DAZ gene cluster described in our previous report should be re-categorized as complete AZFc deletions. The disparity stems from highly similar nucleotide sequences between the members of the gene families. For example, the coding regions of CDY1 and CDY2 are 99% identical in nucleotide sequences. Such a high degree of nucleotide similarity implies the importance of critical quality control for PCR analysis. The observation that BPY2, CDY1 and DAZ genes are deleted simultaneously in cases with complete AZFc deletion is consistent with the model of Kuroda-Kawaguchi et al. [7]. In light of the uniform deletion pattern observed, other gene families located within the AZFc region, that is, CSPG4LY, GOLGA2LY, TTTY3 and TTTY4, are believed to be deleted in our patients.

The relationship between the AZFc deletion and testicular phenotypes is still not apparent, despite uniform deletion junctions in nearly all patients. Twenty-three men with uniform AZFc deletion junctions possessed different testicular phenotypes, ranging from moderate oligozoospermia (sperm count between 5.0×10⁶/mL and 10.0×10⁶/mL), to severe oligozoospermia (sperm count (5.0×10⁶/mL), to azoospermia with hypospermatogenesis or maturation arrest. This finding is in agreement with previous studies that show that identicalAZFc deletion might be associated with a different impairmentof spermatogenesis and might not exclude the occurrence of spontaneous pregnancy [15, 16]. The implications of this finding are 2-fold. First, the human AZFc genes are not essential for sustained fertility. Some AZFc-deleted men will retain fertility and are capable of complete spermatogenesis. Second, the testicular phenotypes are modified by autosomal genes or other genetic back-grounds. The presence of the 45,X cell line illustrates the interactions between Y-linked sterile genes and other genetic backgrounds of patients. Mosaicism for 45,X cell lines might accentuate the severity of spermatogenic defects in men with AZFc deletions [17]. Autosomal genes have been shown to be associated with impaired production of human sperm [18]. Studies on how Y-linked sterility-associated genes interact with autosomal or X-chromosomal genes will provide further insight into the genetic pathways involved in human spermatogenesis.

The major obstacle in elucidating the roles of sterili-ty-related genes stems from the complex and highly polymorphic genomic organization of the human Y chromo-some. AZFc is almost entirely made up of long direct and inverted repeats (amplicons). Members of each amplicon family are more than 99% identical in genomic sequences, and such genomic structure is especially prone to amplification or deletion. It is highly likely that the amplicons vary in size or copy number within the population. Of the gene families located within the AZFc region, the DAZ gene cluster consists of four copies, the BPY2 gene cluster consists of three copies, and the CDY1 gene cluster consists of two copies [7]. However, the copy number of the DAZ gene may range from 4 to 7 according to different investigators [19, 20]. The copy number of BPY2, CDY1 or other sterility-associated genes located within the AZFc region may vary significantly. It would be highly desirable to study the detailed organization of the AZFc region in different ethnic groups and in patients with spermatogenic defect.

Partial AZFc deletion cannot be detected by the protocol described in this study because PCR analysis only reveals “all or none” results. Partial deletion of the DAZ gene cluster has been reported to account for 5%-10% of cases of oligozoospermia and azoospermia [12, 13]. Likewise, partial deletion of BPY2 or CDY1 may be asso-ciated with various degrees of spermatogenic defect [18]. PCR amplification-restriction digestion assay, fiber fluorescence in situ hybridization, Southern blot analysis, or quantitative PCR will be helpful in detecting the copy numbers of Y-linked sterile genes and to delineate subgroups of patients with spermatogenic defect.

In conclusion, we identified a group of infertile men in Taiwan with complete AZFc deletion and uniform deletion junctions. Both proximal and distal deletion junctions were identical to the previous report by Kuroda-Kawaguchi et al. [7]. Despite a homogeneous genetic defect in the Y chromosome, no clear genotype/phenotype correlation could be demonstrated in patients with complete AZFc deletion.

Acknowledgment

This study was sponsored by research grants from the National Science Council of Taiwan (NSC- 91-2314-B-006-149, NSC-90-2314-B-006-164, NSC-90-2314-B-006-168, and NSC-91-3112-B-006-008) and the Tainan Phoenix Urological Research and Education Foundation (TPUREF 9001).

References

1 Vogt PH, Edelmann A, Kirsch S, Henegariu O, Hirschmann P, Kiesewetter F, et al. Human Y chromosome azoospermia factors (AZF) mapped to different subregions in Yq11. Hum Mol Genet 1996; 5: 933-43.

2 Chiang HS, Yeh SD, Wu CC, Huang BC, Tsai HJ, Fang CL.Clinical and pathological correlation of the microdeletion of Y chromosome for the 30 patients with azoospermia and severe oligoasthenospermia. Asian J Androl 2004; 6: 369-75.

3 El Awady MK, El Shater SF, Ragaa E, Atef K, Shaheen IM, Megiud NA.Molecular study on Y chromosome microdele-tions in Egyptian males with idiopathic infertility. Asian J Androl 2004; 6:53-7.

4 Babu SR, Swarna M, Padmavathi P, Reddy PP.PCR analysis of Yq microdeletions in infertile males, a study from South India. Asian J Androl 2002; 4: 265-8.

5 Lin YM, Lin YH, Teng YN, Hsu CC, Lin JSN, Kuo PL. Gene-based screening for Y chromosome deletions in Taiwanese men presenting with spermatogenic failure. Fertil Steril 2002; 77: 897-903.

6 Dada R, Gupta NP, Kucheria K.AZFmicrodeletions associated with idiopathic and non-idiopathic cases with cryptorchidism and varicocele. Asian J Androl 2002; 4: 259-63.

7 Kuroda-Kawaguchi T, Skaletsky H, Brown LG, Minx PJ, Cordum HS, Waterston RH, et al. The AZFc region of the Y chromosome features massive palindromes and uniform recurrent deletions in infertile men. Nat Genet 2001; 29: 279-86.

8 Skaletsky H, Kuroda-Kawaguchi T, Minx PJ, Cordum HS, Hillier L, Brown LG, et al. The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes. Nature 2003; 423: 825-37.

9 Kamp C, Hirschmann P, Voss H, Huellen K, Vogt PH. Two long homologous retroviral sequence blocks in proximal Yq11 cause AZFa microdeletions as a result of intrachromosomal recombination events. Hum Mol Genet 2000; 9: 2563-72.

10 Repping S, Skaletsky H, Lange J, Silber S, Van Der Veen F, Oates RD, et al. Recombination between palindromes P5 and P1 on the human Y chromosome causes massive deletions and spermatogenic failure. Am J Hum Genet 2002; 71: 906-22.

11 Repping S, Skaletsky H, Brown L, van Daalen SK, Korver CM, Pyntikova T, et al. Polymorphism for a 1.6-Mb deletion of the human Y chromosome persists through balance between recurrent mutation and haploid selection. Nat Genet 2003; 35: 247-51.

12 Repping S, van Daalen SK, Korver CM, Brown LG, Marszalek JD, Gianotten J, et al. A family of human Y chromosomes has dispersed throughout northern Eurasia despite a 1.8-Mb deletion in the azoospermia factor c region. Genomics 2004; 83: 1046-52.

13 Ferlin A, Tessari A, Ganz F, Marchina E, Barlati S, Garolla A, et al. Association of partial AZFc region deletions with spermatogenic impairment and male infertility. J Med Genet 2005; 42: 209-13.

14 Ferlin A, Moro E, Rossi A, Foresta C. CDY1 analysis in infer-tile patients with DAZ deletions. J Endocrinol Invest 2001; 24: RC4-6.

15 Chang PL, Sauer MV, Brown S. Y chromosome microdeletion in a father and his four infertile sons. Hum Reprod 1999; 14: 2689-94.

16 Gatta V, Stuppia L, Calabrese G, Morizio E, Guanciali-Franchi P, Palka G. A new case of Yq microdeletion transmitted from a normal father to two infertile sons. J Med Genet 2002; 39: E27.

17 Jaruzelska J, Korcz A, Wojda A, Jedrzejczak P, Bierla J, Surmacz T, et al. Mosaicism for 45,X cell line may accentuate the severity of spermatogenic defects in men with AZFc deletion. J Med Genet 2001; 38: 798-802.

18 Teng YN, Lin YM, Lin YH, Tsao SY, Hsu CC, Lin JSN, et al. Association of a single nucleotide polymorphism of the deleted-in-azoospermia-like gene with susceptibility to spermatogenic failure. J Clinl Endocrinol Metab 2002; 87: 5258-64.

19 Moro E, Ferlin A, Yen PH, Franchi PG, Palka G, Foresta C. Male infertility caused by a de novo partial deletion of the DAZ cluster on the Y chromosome. J Clinl Endocrinol Metab 2000; 85: 4069-73.

20 Saxena R, de Vries JW, Repping S, Alagappan RK, Skaletsky H, Brown LG, et al. Four DAZ genes in two clusters found in the AZFc region of the human Y chromosome. Genomics 2000; 67: 256-67.