1 Department of Paediatrics, Obstetrics and Reproductive Medicine, Section of Biology, University of Siena, 2 Regional Referral Center for Male Infertility, Azienda Ospedaliera Senese, Siena and 3 Department of Pathological Anatomy and Genetics D.A.P.E.G, University of Bari, Bari, Italy
4 To whom correspondence should be addressed at: Department of Paediatrics, Obstetrics and Reproductive Medicine, Section of Biology, via T. Pendola 62, 53100 Siena, Italy. e-mail: baccetti{at}unisi.it
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Abstract |
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Key words: electron microscopy/fluorescence in-situ hybridization/male infertility/reciprocal translocation/spermatozoa
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Introduction |
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The possible correlation between human male infertility due to impaired spermatogenesis and chromosome anomalies (mainly translocations) was postulated almost 30 years ago (Chandley, 1975; 1976). Likewise, others (Plymate et al., 1976
; Leonard et al., 1979
) found a correlation between derangement of spermatogenesis and autosomal translocations. Recently, the correlation between chromosomal anomalies and human male infertility has become more evident. One group (Pellestor et al., 2001
) reported oligoteratozoospermia in carriers of reciprocal or Robertsonian chromosomal translocation; nevertheless, they found normal sperm number and motility in males with different structural chromosomal anomalies. Other authors (Marmor et al., 1980
; Matsuda et al., 1991
; Testart et al., 1996
), when examining the morphology and motility of human spermatozoa with light microscopy, did not find any correlation between sperm quality and chromosome translocations or inversions.
Electron microscopy enables more detailed evaluation of sperm alterations (Baccetti, 1984; Zamboni, 1987
; Bartoov et al., 1994
; Chemes et al., 1998
), and permits a distinction to be made between phenotypic and genotypic defects (Baccetti, 2000
; Baccetti et al., 2001
). Hereditary male sterility due to genotypic sperm defects is a possibility. The original idea of generic human male infertility correlated to chromosome anomalies could give way to the concept that male infertility is due to particular defects, caused by chromosome anomalies, heralding research into the genes responsible for hereditary sperm characteristics and their mutations. Recently, fibrous sheath dysplasia of stump spermatozoa was associated with pericentric inversion of chromosome 9 (Baccetti et al., 1997
). However, the clearest connection between a sterilizing human sperm defect and a specific chromosome alteration was the discovery of mutations in the DNAI1 gene, mapping to 9 p13-p21, in three Kartageners syndrome patients (Blouin et al., 2000
; Guichard et al., 2001
). In studying the association between chromosome mutations and sperm defects in sterile men, immature sperm were found in a human carrier of Robertsonian translocation 14;22 (Baccetti et al., 2002
). This anomaly was most likely in a chromosome region involved in spermatogenesis.
Herein, peculiar ultrastructural sperm defects are described in a sterile male carrier of a balanced translocation t(10;15) (q26;q12). Fluorescence in-situ hybridization (FISH) was used in decondensed sperm nuclei to evaluate chromosomes 10, 15 segregation and possible interchromosomal effects, detected through an increase in aneuploidy frequencies of chromosomes 18, X, Y that were not involved in the translocation.
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Materials and methods |
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Karyotype
Conventional cytogenetic analysis of 2448 h cultures of blood lymphocytes of the patient and his parents was performed using standard techniques and evaluated by Giemsa-Trypsin-Giemsa (GTG) banding at about the 400 band level according to the 1995 International System for Human Cytogenetic Nomenclature (ISCN, 1995).
Karyotype FISH analysis was performed with a painting probe for chromosome 15, obtained from humanhamster hybrid (GM11418) retaining chromosome 15 as the only human contribution (a kind gift from the Coriell Institute for Medical Research, NJ, USA).
DNA from the hybrid was dual Alu-PCR amplified according to published methods (Liu et al., 1993). The PCR products were biotin-labelled by nick translation and used as probe for FISH experiments on chromosome metaphases of phytohaemagglutinin (PHA)-stimulated peripheral blood lymphocytes of the patient. Chromosome preparations were hybridized in situ essentially as described previously (Lichter et al., 1990
), albeit with minor modifications (Marzella et al., 1997
). In FISH experiments, chromosomes were identified by diamino-phenylindole (DAPI) counterstaining, and digital images obtained using a Leika epifluorescence microscope equipped with a cooled charge-coupled device (CCD) camera. Cy3 (Amersham) and DAPI fluorescence signals were recorded separately as grey-scale images. Pseudocolouring and merging were performed using commercial Adobe Photoshop software.
Light and electron microscopy
Semen samples were obtained by masturbation after 4 days of sexual abstinence and examined after liquefaction for 30 min at 37°C. Volume, pH, concentration and motility were evaluated following published guidelines (World Health Organization, 1999). Semen analysis was performed three times at 6-month intervals.
For electron microscopy, a single sperm sample was fixed in cold Karnovsky fixative and maintained at 4°C for 2 h. Fixed semen was washed in 0.1 mol/l cacodylate buffer (pH 7.2) for 12 h, postfixed for 1 h at 4°C in 1% buffered osmium tetroxide, dehydrated, and embedded in Epon Araldite. Ultra-thin sections were cut with a Supernova ultramicrotome (Reickert Jung, Vienna, Austria), mounted onto copper grids, stained with uranyl acetate and lead citrate, observed and photographed with a Philips CM 10 transmission electron microscope (TEM; Philips Scientifics, Eindhoven, The Netherlands). A total of 300 ultra-thin sperm sections was examined for major submicroscopic characteristics. TEM data were evaluated using a mathematical formula (Baccetti et al., 1995).
An aliquot from the same sperm sample was also processed for scanning electron microscopy (SEM), fixing the spermatozoa as described above and smearing them onto poly-lysine (1%) -coated coverslips. After dehydration, specimens were dried using the critical point technique, coated in gold and examined using a Philips CM 515 scanning electron microscope (Philips Scientifics).
FISH analysis of spermatozoa
An aliquot from the same sperm sample as used for TEM and SEM analyses was washed with 150 mmol/l NaCl and 10 mmol/l TrisHCl (pH 8), smeared onto glass slides and air-dried. Slides were then fixed in methanol:acetic acid (3:1) for 10 min, dehydrated in 70, 80 and 100% cold ethanol, and air-dried. Samples were swell-treated with 0.01 mol/l dithiothreitol (Biorad) in 0.1 mol/l TrisHCl (pH 8), followed by 20 mmol/l 3,5-diiodosalicylic acid, lithium salt (Sigma) in the same buffer, checking sperm head swelling. The slides, rinsed in 2x standard saline citrate (SSC), pH 7, air-dried and then dehydrated and denatured in 70% formamide (Aldrich) 2x SSC at 73° for 4 min. Slides were then quickly dehydrated in a graded ethanol series at 0°C and air-dried. During this last step, chromosome enumeration probes (Vysis, IL, USA), -satellite DNA probes for chromosomes X, Y, 10, 15 and 18 directly labelled with different fluorochromes, were used. Moreover, self-made telomeric probes RP11-10D13 for 10p, RP11-108K14 for 10q and RP11-9B21 for 15q, were used to distinguish alternate and adjacent-1 segregations.
The probe mix was denatured for 5 min at 73°C in a water bath. Hybridization was carried out at 37°C in a moist chamber for 12 h. The slides were then washed with 0.4x SSC0.3% Nonidet P40 (NP40) for 2 min at 73°C, quickly in 2x SSC0.1% NP40 at room temperature, and finally mounted with DAPI 125 ng/ml in antifade solution (Vysis). In total, 3023 spermatozoa were analysed using triple-colour FISH (18, X, Y), 2606 were scored by dual-colour FISH (10, 15), and 2100 sperm cells were examined with telomeric probes.
Scoring criteria
The overall hybridization efficiency was >99%. Sperm nuclei were scored according to published criteria (Martin and Rademaker, 1995). According to these criteria, sperm nuclei are scored only if they are intact, non-overlapping and have a clearly defined border. In the case of aneuploidy, the presence of a sperm tail was confirmed. A spermatozoon was considered disomic if the two fluorescent spots were of the same colour, comparable in size, shape and intensity and positioned inside the edge of the sperm head at least one domain apart. Diploidy was recognized by the presence of two double fluorescent spots, following the above criteria. Observation and scoring was performed on a Leitz Aristoplan Optic Microscope equipped with fluorescence apparatus, with a triple bandpass filter for Aqua, Orange, Green Fluorochromes (Vysis) and a monochrome filter for DAPI.
Controls
Semen samples from seven healthy normal men (age range 2639 years) were collected to constitute a control group. All subjects were of proven fertility and showed normal seminal parameters, according to published guidelines (World Health Organization, 1999). Ultrastructural analysis evaluated by the mathematical formula (Baccetti et al., 1995
) confirmed that sperm quality was in the range of natural fertility.
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Results |
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FISH analysis on chromosomal metaphases from blood lymphocytes using specific painting probes for chromosome 15 showed a reciprocal translocation involving chromosomes 10 and 15 (Figure 1). Chromosome 15 showed the breakpoint at 15q12 and chromosome 10 at 10q26, giving rise to der(10)t(10;15) and der(15)t(10;15).
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Meiotic segregation in the t(10;15) (10q26;15q12) translocation carrier was investigated by FISH. The aneuploidy frequencies of chromosomes 18, X and Y, not involved in the translocation, are summarized in Table II. A very high value of chromosome 18 disomy and diploidies (particularly 1818XX and 1818XY) was found in comparison with values of the control group (Table II). FISH analysis of chromosomes involved in translocation (10;15) showed a very high percentage of chromosome 10 disomy and diploidy (Table III).
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With regard to the meiotic process, by using dual-colour FISH 93.4% of sperm were found with both 10, 15 chromosome signals, indicating an alternate or adjacent-1 segregation pattern. The products of adjacent-2 segregation were 2.8%, and those of 3:1 segregation 2.4%, of total products. By using FISH with telomeric probes for chromosomes 10, 15 it was possible to distinguish alternate segregation (producing balanced gametes) in 32.8% of sperm from other segregation patterns, all of which generated unbalanced gametes in 68.2% of sperm.
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Discussion |
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In infertile men, structural chromosomal anomalies occur more frequently than in the general population (Van Assche et al., 1996; Kalantari et al., 2001
). Semen analysis carried out in a large population of infertile males (Bourrouillou et al., 1997
; Pandiyan and Jequier, 1996
) revealed a strong correlation between the rate of chromosomal anomalies and the severity of oligozoospermia. Other authors (Pellestor et al., 2001
) observed oligoteratozoospermia in carriers of structural chromosomal alterations. Nevertheless, morphological sperm quality is always evaluated with optical microscopy, sometimes applying Krugers strict criteria. Structural sperm anomalies can be highlighted only by the use of electron microscopy, which allows detailed evaluation of inner sperm organelles. By using this method, one group (Quintana de la Rosa et al., 2001
) reported a generalized flagellar abnormality in an infertile man carrier of t (3;22), while others (Baccetti et al., 2002
) observed an unusual structural sperm immaturity in a sterile carrier of t(14;22). In the present report, the electron microscopic analysis of ejaculated spermatozoa from an infertile male carrier of reciprocal translocation 10;15, demonstrated severe ultrastructural sperm alterations, indicating diffuse sperm immaturity. Nevertheless, no particular monomorphic sperm defect was observed which affected the entire sperm population, as reviewed previously (Baccetti et al., 2001
).
Derangement of meiotic segregation is indicated by the abnormal chromosomal constitution of spermatozoa detected using FISH analysis. The high frequency of chromosome 18 disomy could be considered as a positive interchromo somal effect. This effect depends on the type of structural reorganization, the chromosomes involved and the chromosome breakpoints (Blanco et al., 2000; Anton et al., 2002
), and results in a particular meiotic behaviour, namely unsynapsed regions or preferential meiotic configurations that could lead to the observed increase in chromosome 18 disomies.
Moreover, the high frequency of sperm diploidies detected by dual- and triple-colour FISH, using centromeric probes, indicates incomplete meiosis process leading to immature sperm cells with double nuclei, as observed by TEM, or with a double chromosome set. Dual-colour FISH performed in sperm nuclei highlighted the segregation pattern of chromosomes 10 and 15 involved in the translocation. The detection of both signals in 93.4% of sperm indicated alternate or adjacent-1 segregation patterns, producing normal, balanced or unbalanced gametes. The products of adjacent-2 segregation (2.8%) and 3:1 segregation (2.4%) were certainly unbalanced gametes. By using triple-colour FISH and telomeric probes it was shown that 32.8% of sperm were balanced, but 68.2% were unbalanced. These data were in agreement with previous reports of between 19 and 77% of the spermatozoa of reciprocal translocation carriers being chromosomally unbalanced, while about 50% were chromosomally abnormal (Martin and Spriggs, 1995; Shi and Martin, 2001
).
In conclusion, in this male carrier of a reciprocal translocation t(10;15), the existence of a correlation is proposed between these diffuse ultrastructural sperm alterations and the high frequency of sperm aneuploidies. Ultrastructural findings indicated very poor sperm quality incompatible with natural fertility and, as in all cases of immature sperm, the only possibility for fertilization is ICSI. However, the results obtained with karyotyping and FISH analysis in the present patient contraindicate the use of artificial reproduction techniques due to the high risk of imbalances in zygotes or fetus in reciprocal translocation carriers.
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Acknowledgements |
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Submitted on March 13, 2003; resubmitted on June 16, 2003; accepted on July 25, 2003.