An azoospermic man with a double-strand DNA break-processing deficiency in the spermatocyte nuclei: case report

Research progress on the fanconi anemia signaling pathway in non-obstructive azoospermia

Non-obstructive azoospermia (NOA) is a disease characterized by spermatogenesis failure and comprises phenotypes such as hypospermatogenesis, mature arrest, and Sertoli cell-only syndrome. Studies have shown that FA cross-linked anemia (FA) pathway is closely related to the occurrence of NOA. There are FA gene mutations in male NOA patients, which cause significant damage to male germ cells. The FA pathway is activated in the presence of DNA interstrand cross-links; the key step in activating this pathway is the mono-ubiquitination of the FANCD2-FANCI complex, and the activation of the FA pathway can repair DNA damage such as DNA double-strand breaks. Therefore, we believe that the FA pathway affects germ cells during DNA damage repair, resulting in minimal or even disappearance of mature sperm in males. This review summarizes the regulatory mechanisms of FA-related genes in male azoospermia, with the aim of providing a theoretical reference for clinical research and exploration of related genes.

RAD51 and Infertility: A Review and Case-Control Study

RAD51 is a highly conserved recombinase involved in the strand invasion/exchange of double-stranded DNA by homologous single-stranded DNA during homologous recombination repair. Although a majority of existing literature associates RAD51 with the pathogenesis of various types of cancer, recent reports indicate a role of RAD51 in maintenance of fertility. The present study reviews the role of RAD51 and its interacting proteins in spermatogenesis/oogenesis and additionally reports the findings from the molecular genetic screening of RAD51 135 G > C polymorphism in infertile cases and controls. Fifty-nine articles from PubMed and Google Scholar related to the reproductive role of RAD51 were reviewed. For case-control study, the PCR-RFLP method was used to screen the RAD51 135 G > C polymorphism in 201 infertile cases (100 males, 101 females) and 201 age- and gender-matched healthy controls (100 males, 101 females) from Punjab, North-West India. The review of literature shows that RAD51 is indispensable for spermatogenesis and oogenesis in animal models. Reports on the role of RAD51 in human fertility are limited, however it is involved in the pathogenesis of infertility in both males and females. Molecular genetic analyses in the infertile cases and healthy controls showed no statistically significant difference in the genotypic and allelic frequencies for RAD51 135 G > C polymorphism, even after segregation of the cases by type of infertility (primary/secondary). Therefore, the present study concluded that the RAD51 135 G > C polymorphism was neither associated with male nor female infertility in North-West Indians. This is the first report on RAD51 135 G > C polymorphism and infertility.

Therapeutic Dose of Hydroxyurea-Induced Synaptic Abnormalities on the Mouse Spermatocyte

Hydroxyurea (HU) is a widely used pharmacological therapy for sickle cell disease (SCD). However, replication stress caused by HU has been shown to inhibit premeiotic S-phase DNA, leading to reproductive toxicity in germ cells. In this study, we administered the therapeutic doses of HU (i.e., 25 and 50 mg/kg) to male mice to explore whether replication stress by HU affects pachytene spermatocytes and causes the abnormalities of homologous chromosomes pairing and recombination during prophase I of meiosis. In comparison with the control group, the proportions of spermatocyte gaps were significantly different in the experimental groups injected with 25 mg/kg (p < 0.05) and 50 mg/kg of HU (p < 0.05). Moreover, the proportions of unrepaired double-stranded breaks (DSBs) observed by γH2AX staining also corresponded to a higher HU dose with a greater number of breaks. Additionally, a reduction in the counts of recombination foci on the autosomal SCs was observed in the pachytene spermatocytes. Our results reveal that HU has some effects on synaptonemal complex (SC) formation and DSB repair which suggest possible problems in fertility. Therefore, this study provides new evidence of the mechanisms underlying HU reproductive toxicity.

Meiotic Double-Strand Break Processing and Crossover Patterning Are Regulated in a Sex-Specific Manner by BRCA1-BARD1 in Caenorhabditis elegans

Meiosis is regulated in a sex-specific manner to produce two distinct gametes, sperm and oocytes, for sexual reproduction. To determine how meiotic recombination is regulated in spermatogenesis, we analyzed the meiotic phenotypes of mutants in the tumor suppressor E3 ubiquitin ligase BRC-1-BRD-1 complex in Caenorhabditis elegans male meiosis. Unlike in mammals, this complex is not required for meiotic sex chromosome inactivation, the process whereby hemizygous sex chromosomes are transcriptionally silenced. Interestingly, brc-1 and brd-1 mutants show meiotic recombination phenotypes that are largely opposing to those previously reported for female meiosis. Fewer meiotic recombination intermediates marked by the recombinase RAD-51 were observed in brc-1 and brd-1 mutants, and the reduction in RAD-51 foci could be suppressed by mutation of nonhomologous-end-joining proteins. Analysis of GFP::RPA-1 revealed fewer foci in the brc-1brd-1 mutant and concentration of BRC-1-BRD-1 to sites of meiotic recombination was dependent on DNA end resection, suggesting that the complex regulates the processing of meiotic double-strand breaks to promote repair by homologous recombination. Further, BRC-1-BRD-1 is important to promote progeny viability when male meiosis is perturbed by mutations that block the pairing and synapsis of different chromosome pairs, although the complex is not required to stabilize the RAD-51 filament as in female meiosis under the same conditions. Analyses of crossover designation and formation revealed that BRC-1-BRD-1 inhibits supernumerary COs when meiosis is perturbed. Together, our findings suggest that BRC-1-BRD-1 regulates different aspects of meiotic recombination in male and female meiosis.

Meiotic arrest occurs most frequently at metaphase and is often incomplete in azoospermic men

OBJECTIVE

To establish which meiotic checkpoints are activated in males with severe spermatogenic impairment to improve phenotypic characterization of meiotic defects.

DESIGN

Retrospective observational study.

SETTING

University medical center research laboratory and andrology clinic.

PATIENT(S)

Forty-eight patients with confirmed spermatogenic impairment (Johnsen scores 3-6) and 15 controls (Johnsen score 10).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Quantitative assessment of immunofluorescent analyses of specific markers to determine meiotic entry, chromosome pairing, progression of DNA double-strand break repair, crossover formation, formation of meiotic metaphases, metaphase arrest, and spermatid formation, resulting in a novel classification of human meiotic arrest types.

RESULT(S)

Complete metaphase arrest was observed most frequently (27%), and the patients with the highest frequency of apoptotic metaphases also displayed a reduction in crossover number. Incomplete metaphase arrest was observed in 17% of the patients. Only four patients (8%) displayed a failure to complete meiotic chromosome pairing leading to pachytene arrest. Two new types of meiotic arrest were defined: premetaphase and postmetaphase arrest (15% and 13%, respectively).

CONCLUSION(S)

Meiotic arrest in men occurs most frequently at meiotic metaphase. This arrest can be incomplete, resulting in low numbers of spermatids, and often occurs in association with reduced crossover frequency. The phenotyping approach described here provides mechanistic insights to help identify candidate infertility genes and to assess genotype-phenotype correlations in individual cases.

Pseudosynapsis and decreased stringency of meiotic repair pathway choice on the hemizygous sex chromosome of Caenorhabditis elegans males

During meiosis, accurate chromosome segregation relies on homology to mediate chromosome pairing, synapsis, and crossover recombination. Crossovers are dependent upon formation and repair of double-strand breaks (DSBs) by homologous recombination (HR). In males of many species, sex chromosomes are largely hemizygous, yet DSBs are induced along nonhomologous regions. Here we analyzed the genetic requirements for meiotic DSB repair on the completely hemizygous X chromosome of Caenorhabditis elegans males. Our data reveal that the kinetics of DSB formation, chromosome pairing, and synapsis are tightly linked in the male germ line. Moreover, DSB induction on the X is concomitant with a brief period of pseudosynapsis that may allow X sister chromatids to masquerade as homologs. Consistent with this, neither meiotic kleisins nor the SMC-5/6 complex are essential for DSB repair on the X. Furthermore, early processing of X DSBs is dependent on the CtIP/Sae2 homolog COM-1, suggesting that as with paired chromosomes, HR is the preferred pathway. In contrast, the X chromosome is refractory to feedback mechanisms that ensure crossover formation on autosomes. Surprisingly, neither RAD-54 nor BRC-2 are essential for DSB repair on the X, suggesting that unlike autosomes, the X is competent for repair in the absence of HR. When both RAD-54 and the structure-specific nuclease XPF-1 are abrogated, X DSBs persist, suggesting that single-strand annealing is engaged in the absence of HR. Our findings indicate that alteration in sister chromatid interactions and flexibility in DSB repair pathway choice accommodate hemizygosity on sex chromosomes.

History and evolution of cytogenetics

The events that have led to the development of cytogenetics as a specialty within the life sciences are described, with special attention to the early history of human cytogenetics. Improvements in the resolution of chromosome analysis has followed closely the introduction of innovative technology. The review provides a brief account of the structure of somatic and meiotic chromosomes, stressing the high conservation of structure in plants and animals, with emphasis on aspects that require further research. The future of molecular cytogenetics is likely to depend on a better knowledge of chromosome structure and function.

Decreased XY recombination and disturbed meiotic prophase I progression in an infertile 48, XYY, +sSMC man

Small supernumerary marker chromosomes (sSMCs) are structurally abnormal rare chromosomes, difficult to characterize by karyotyping, and have been associated with minor dysmorphic features, azoospermia, and recurrent miscarriages. However, sSMC with a gonosomal trisomy has never been reported. Spermatocyte spreading and immunostaining were applied to detect meiotic prophase I progression, homologous chromosome pairing, synapsis, and recombination. In all the analyzed spermatocytes of the patient, the extra Y chromosome was not detected while the sSMC was present. The recombination frequency on autosomes was not affected, while the recombination frequencies on XY chromosome was significantly lower in the patient than in the controls. The meiotic prophase I progression was disturbed with significantly increased proportion of zygotene and decreased pachytene spermatocytes in the patients as compared with the controls. These findings highlight the importance of studies on meiotic behaviors in patients with an abnormal chromosomal constitution and provide an important framework for future studies, which may elucidate the impairment caused by sSMC in mammalian meiosis and fertility.

Ultrastructural and immunofluorescent methods for the study of the XY body as a biomarker

Structural and immunohistochemical methods have been extremely useful for the characterization of the XY body (the structure formed by the XY pair during meiotic prophase) in Man and in other mammals. These methods are widely used at the present time for the detection of abnormalities leading to human infertility. The basic ultrastructural methods are spreading of pachytene spermatocytes, thin-sectioning techniques with or without 3-D reconstructions, and the monitoring of all specimens with semi-thin sections. Immunofluorescent techniques also use spreading of meiotic cells for the analysis of the XY body, and they can be combined with the fluorescence in situ hybridization (FISH) technique, in the so-called immuno-FISH. Epitope retrieval techniques are also used.

DNA mismatch repair and infertility

PURPOSE OF REVIEW

To highlight the significance of the abnormal DNA repair mechanism in male infertility.

RECENT FINDINGS

DNA repair defects cause a variety of spermatogenic defects in mouse models. Evidence is accumulating to demonstrate the importance of DNA repair defects in human nonobstructive azoospermia. Epigenetic changes may also play a crucial role in infertility.

SUMMARY

The DNA in the cell needs to be constantly repaired to ensure fidelity of DNA replication, to maintain genome stability and to ensure propagation of species. The DNA repair and recombination machineries are highly conserved across the species and inactivation of these pathways may lead to replication and recombination errors. This review summarizes the different types of DNA lesions and DNA repair pathways, particularly focusing on highly conserved meiotic regulators, the DNA mismatch repair proteins. Targeted deletions of some of these proteins result in infertility and predisposes to tumor in mutant mouse models. There is evidence for loss of some of these proteins in human male infertility. Because defective DNA repair is associated with a mutator phenotype, the risk of transmission to the offspring of these otherwise infertile men conceived using an assisted reproductive technology needs further evaluation.

Genetic probing of homologous recombination and non-homologous end joining during meiotic prophase in irradiated mouse spermatocytes

This study was designed to obtain a better insight into the relative contribution of homologous recombination (HR) and non-homologous end joining (NHEJ) to the repair of radiation-induced DNA double-strand breaks (DSBs) at first meiotic prophase. Early and late pachytene and early diplotene spermatocytes that had completed crossing over were sampled. We studied the kinetics of gamma-H2AX chromatin foci removal after irradiation of mice deficient for HR and mice deficient for NHEJ. Analyzing gamma-H2AX signals in unirradiated RAD54/RAD54B deficient spermatocytes indicated incomplete meiotic recombination repair due to the pronounced increase of gamma-H2AX foci in late prophase primary spermatocytes. In these mice, 8h after irradiation, early pachytene spermatocytes showed a reduction of the numbers of gamma-H2AX foci by 52% compared to 82% in the wild type, the difference being significant. However, after crossing over (in late pachytene and early diplotene), no effect of RAD54/RAD54B deficiency on the reduction of irradiation-induced foci was observed. In NHEJ deficient SCID mice, repair kinetics in early spermatocytes were similar to those in wild type mice. However, 1h after irradiation in late pachytene and early diplotene spermatocytes 1.7 times more foci were found than in wild type mice. This difference might be related to the absence of a DNA-PKcs dependent fast repair component in SCID mice. As subsequent repair is normal, HR likely is taking over. Taken together, the results obtained in RAD54/RAD54B deficient mice and in SCID mice indicate that DSB repair in early pachytene spermatocytes is mainly carried out through HR. In late spermatocytes (late pachytenes and early diplotenes) NHEJ is active. However, probably there is an interplay between these repair pathways and when in late spermatocytes the NHEJ pathway is compromised HR may take over.

A high incidence of meiotic silencing of unsynapsed chromatin is not associated with substantial pachytene loss in heterozygous male mice carrying multiple simple robertsonian translocations

Meiosis is a complex type of cell division that involves homologous chromosome pairing, synapsis, recombination, and segregation. When any of these processes is altered, cellular checkpoints arrest meiosis progression and induce cell elimination. Meiotic impairment is particularly frequent in organisms bearing chromosomal translocations. When chromosomal translocations appear in heterozygosis, the chromosomes involved may not correctly complete synapsis, recombination, and/or segregation, thus promoting the activation of checkpoints that lead to the death of the meiocytes. In mammals and other organisms, the unsynapsed chromosomal regions are subject to a process called meiotic silencing of unsynapsed chromatin (MSUC). Different degrees of asynapsis could contribute to disturb the normal loading of MSUC proteins, interfering with autosome and sex chromosome gene expression and triggering a massive pachytene cell death. We report that in mice that are heterozygous for eight multiple simple Robertsonian translocations, most pachytene spermatocytes bear trivalents with unsynapsed regions that incorporate, in a stage-dependent manner, proteins involved in MSUC (e.g., gammaH2AX, ATR, ubiquitinated-H2A, SUMO-1, and XMR). These spermatocytes have a correct MSUC response and are not eliminated during pachytene and most of them proceed into diplotene. However, we found a high incidence of apoptotic spermatocytes at the metaphase stage. These results suggest that in Robertsonian heterozygous mice synapsis defects on most pachytene cells do not trigger a prophase-I checkpoint. Instead, meiotic impairment seems to mainly rely on the action of a checkpoint acting at the metaphase stage. We propose that a low stringency of the pachytene checkpoint could help to increase the chances that spermatocytes with synaptic defects will complete meiotic divisions and differentiate into viable gametes. This scenario, despite a reduction of fertility, allows the spreading of Robertsonian translocations, explaining the multitude of natural Robertsonian populations described in the mouse.

ATR, BRCA1 and gammaH2AX localize to unsynapsed chromosomes at the pachytene stage in human oocytes

Asynapsis of homologous chromosomes at the pachytene stage has been associated with gametogenic failure and infertility, but the cellular mechanisms involved are currently unknown in human meiocytes. In mice, the protein encoded by the breast-cancer susceptibility gene Brca1 has been described to direct kinase ATR (ataxia telangiectasia and Rad3 related) to any unpaired DNA at the pachytene stage, where ATR triggers H2AX phosphorylation, resulting in the silencing of those chromosomes. In this study, the distribution of ATR, BRCA1 and the phosphorylated histone gammaH2AX is assessed by immunofluorescence in human oocytes and it is found that they localize at unpaired chromosomes at the pachytene stage. Evidence is shown to propose that BRCA1, ATR and gammaH2AX in the human may be part of a system such as the one previously described in mouse, which signals unsynapsed chromosomes at pachytene and may lead to their silencing.

Protein immunolocalization supports the presence of identical mechanisms of XY body formation in eutherians and marsupials

The meiotic sex chromosomes of the American marsupials Monodelphis dimidiata and Didelphis albiventris were studied with electron microscopy (EM) and with immunofluorescence localization of meiotic proteins SYCP1 and SYCP3, and proteins essential for meiotic sex chromosome inactivation (MSCI), gamma-H2AX and BRCA1. The chromatin of the non-synaptic X and Y chromosomes contains gamma-H2AX, first as foci and then as homogeneous staining at late stages. The thick and split X and Y axes are labelled with BRCA1 except at one terminus. The bulgings of the axes contain SYCP1 as well as the inner side of the dense plate. The evenly spaced and highly packed chromatin fibres of the conjoined XY body in these species have the same behaviour and the same components (gamma-H2AX in the chromatin, BRCA1 in the axes) as in the XY body of eutherian species. These observations and recent data from the literature suggest that XY body formation is ancestral to the metatherian-eutherian divergence.

Characterization of Spo11-dependent and independent phospho-H2AX foci during meiotic prophase I in the male mouse

Meiotic DNA double strand breaks (DSBs) are indicated at leptotene by the phosphorylated form of histone H2AX (gamma-H2AX). In contrast to previous studies, we identified on both zygotene and pachytene chromosomes two distinct types of gamma-H2AX foci: multiple small (S) foci located along autosomal synaptonemal complexes (SCs) and larger signals on chromatin loops (L-foci). The S-foci number gradually declined throughout pachytene, in parallel with the repair of DSBs monitored by repair proteins suggesting that S-foci mark DSB repair events. We validated this interpretation by showing the absence of S-foci in Spo11(-/-) spermatocytes. By contrast, the L-foci number was very low through pachytene. Based on the analysis of gamma-H2AX labeling after irradiation of spermatocytes, the formation of DSBs clearly induced L-foci formation. Upon DSB repair, these foci appear to be processed and lead to the above mentioned S-foci. The presence of L-foci in wild-type pachytene and diplotene could therefore reflect delayed or unregulated DSB repair events. Interestingly, their distribution was different in Spo11(+/-) spermatocytes compared with Spo11(+/+) spermatocytes, where DSB repair might be differently regulated as a response to homeostatic control of crossing-over. The presence of these L-foci in Spo11(-/-) spermatocytes raises the interesting possibility of yet uncharacterized alterations in DNA or chromosome structure in Spo11(-/-) cells.

Apoptosis and blood–testis barrier during the first spermatogenic wave in the pubertal rat

This research explores the initial assembly of the blood-testis barrier (BTB) during puberty, when a massive physiological apoptosis in the first spermatogenic wave takes place. Fragments of testis from 14- to 20-day-old rats were studied by conventional transmission electron microscopic techniques. Lanthanum hydroxide was used as an intercellular tracer. Light microscopy was used to confirm apoptotic death when paraffin-embedded sections were studied by TUNEL analysis. When the seminiferous cords reached the zygotene-pachytene spermatocyte level, they exhibited abundant apoptotic figures, whereas the remaining segments showed sporadic apoptosis. We found a BTB not yet assembled in the cords with zygotene-pachytene spermatocytes and abundant apoptosis. The observed apoptosis frequency diminished drastically when BTB was organized, as confirmed by the use of the tracer. Our conclusion is that the massive apoptosis found in the zygotene-pachytene spermatocytes between days 14 and 20 coincides with an open BTB. The absence of BTB could be one of the factors causing massive apoptosis of zygotene-pachytene spermatocytes, at least within the time span analyzed. The zygotene-pachytene spermatocytes are left exposed in an open environment instead of being isolated in the adluminal compartment to which they are destined.

The asynaptic chromatin in spermatocytes of translocation carriers contains the histone variant γ-H2AX and associates with the XY body

BACKGROUND

The close apposition of multivalents with the XY body has been repeatedly described in heterozygous carriers of chromosomal rearrangements. Because in many of these carriers spermatogenesis is deeply disturbed at the spermatocyte level, the association of autosomal chromatin with the XY body may impair the spermatocyte life.

METHODS

Testicular biopsies from three men carriers of three different chromosomal rearrangements have been analysed by electron microscopy (EM) and immunolocalization of meiotic proteins.

RESULTS

There is an ordered transition from isolated multivalents at early pachytene to XY body association in late pachytene, as shown in a carrier of a rob t(13;14) translocation by EM and in a reciprocal translocation t(9;14) carrier by immunofluorescence. The non-synapsed ends of the quadrivalent show BRCA1 located on the axes and the variant histone gamma-H2AX located on the chromatin. The area covered by gamma-H2AX increases with the association of the asynaptic ends with the XY body in the t(9;14) carrier, and the area covered with gamma-H2AX in the t(Y;15) carrier is larger than that of the XY body of controls.

CONCLUSIONS

The affinity between the inactive XY body and asynaptic regions of multivalents is given a material basis, and transcriptional inactivation is probably shared by these two chromatin types.