Kinetics of meiosis in azoospermic males: a joint histological and cytological approach

Meiotic Silencing in Pigs: A Case Study in a Translocated Azoospermic Boar

Carriers of balanced constitutional reciprocal translocations usually present a normal phenotype, but often show reproductive disorders. For the first time in pigs, we analyzed the meiotic process of an autosome-autosome translocation associated with azoospermia. Meiotic process analysis revealed the presence of unpaired autosomal segments with histone γH2AX accumulation sometimes associated with the XY body. Additionally, γH2AX signals were observed on apparently synapsed autosomes other than the SSC1 or SSC15, as previously observed in Ataxia with oculomotor apraxia type 2 patients or knock-out mice for the Senataxin gene. Gene expression showed a downregulation of genes selected on chromosomes 1 and 15, but no upregulation of SSCX genes. We hypothesized that the total meiotic arrest observed in this boar might be due to the silencing of crucial autosomal genes by the mechanism referred to as meiotic silencing of unsynapsed chromatin (MSUC).

Disorders of Sex Development-Novel Regulators, Impacts on Fertility, and Options for Fertility Preservation

Disorders (or differences) of sex development (DSD) are a heterogeneous group of congenital conditions with variations in chromosomal, gonadal, or anatomical sex. Impaired gonadal development is central to the pathogenesis of the majority of DSDs and therefore a clear understanding of gonadal development is essential to comprehend the impacts of these disorders on the individual, including impacts on future fertility. Gonadal development was traditionally considered to involve a primary 'male' pathway leading to testicular development as a result of expression of a small number of key testis-determining genes. However, it is increasingly recognized that there are several gene networks involved in the development of the bipotential gonad towards either a testicular or ovarian fate. This includes genes that act antagonistically to regulate gonadal development. This review will highlight some of the novel regulators of gonadal development and how the identification of these has enhanced understanding of gonadal development and the pathogenesis of DSD. We will also describe the impact of DSDs on fertility and options for fertility preservation in this context.

PPP2R3C gene variants cause syndromic 46,XY gonadal dysgenesis and impaired spermatogenesis in humans

Context Most of the knowledge on the factors involved in human sexual development stems from studies of rare cases with disorders of sex development. Here, we have described a novel 46, XY complete gonadal dysgenesis syndrome caused by homozygous variants in PPP2R3C gene. This gene encodes B″gamma regulatory subunit of the protein phosphatase 2A (PP2A), which is a serine/threonine phosphatase involved in the phospho-regulation processes of most mammalian cell types. PPP2R3C gene is most abundantly expressed in testis in humans, while its function was hitherto unknown. Patients and methods Four girls from four unrelated families with 46, XY complete gonadal dysgenesis were studied using exome or Sanger sequencing of PPP2R3C gene. In total, four patients and their heterozygous parents were investigated for clinical, laboratory, immunohistochemical and molecular characteristics. Results We have identified three different homozygous PPP2R3C variants, c.308T>C (p.L103P), c.578T>C (p.L193S) and c.1049T>C (p.F350S), in four girls with 46, XY complete gonadal dysgenesis. Patients also manifested a unique syndrome of extragonadal anomalies, including typical facial gestalt, low birth weight, myopathy, rod and cone dystrophy, anal atresia, omphalocele, sensorineural hearing loss, dry and scaly skin, skeletal abnormalities, renal agenesis and neuromotor delay. We have shown a decreased SOX9-Phospho protein expression in the dysgenetic gonads of the patients with homozygous PPP2R3C variants suggesting impaired SOX9 signaling in the pathogenesis of gonadal dysgenesis. Heterozygous males presented with abnormal sperm morphology and impaired fertility. Conclusion Our findings suggest that PPP2R3C protein is involved in the ontogeny of multiple organs, especially critical for testis development and spermatogenesis. PPPR3C provides insight into pathophysiology, as well as emerging as a potential therapeutic target for male infertility.

Human male meiotic sex chromosome inactivation

In mammalian male gametogenesis the sex chromosomes are distinctive in both gene activity and epigenetic strategy. At first meiotic prophase the heteromorphic X and Y chromosomes are placed in a separate chromatin domain called the XY body. In this process, X,Y chromatin becomes highly phosphorylated at S139 of H2AX leading to the repression of gonosomal genes, a process known as meiotic sex chromosome inactivation (MSCI), which has been studied best in mice. Post-meiotically this repression is largely maintained. Disturbance of MSCI in mice leads to harmful X,Y gene expression, eventuating in spermatocyte death and sperm heterogeneity. Sperm heterogeneity is a characteristic of the human male. For this reason we were interested in the efficiency of MSCI in human primary spermatocytes. We investigated MSCI in pachytene spermatocytes of seven probands: four infertile men and three fertile controls, using direct and indirect in situ methods. A considerable degree of variation in the degree of MSCI was detected, both between and within probands. Moreover, in post-meiotic stages this variation was observed as well, indicating survival of spermatocytes with incompletely inactivated sex chromosomes. Furthermore, we investigated the presence of H3K9me3 posttranslational modifications on the X and Y chromatin. Contrary to constitutive centromeric heterochromatin, this heterochromatin marker did not specifically accumulate on the XY body, with the exception of the heterochromatic part of the Y chromosome. This may reflect the lower degree of MSCI in man compared to mouse. These results point at relaxation of MSCI, which can be explained by genetic changes in sex chromosome composition during evolution and candidates as a mechanism behind human sperm heterogeneity.

Male meiosis: Y keep it silenced?

What drives defective spermatocytes into apoptosis during mid-pachytene? A recent study identifies the first mid-pachytene 'killer' genes: two Y-linked transcription factors, the Zfy1/2 gene pair, must be silenced to avoid apoptosis.

Chromosomal rearrangement interferes with meiotic X chromosome inactivation

Heterozygosity for certain mouse and human chromosomal rearrangements is characterized by the incomplete meiotic synapsis of rearranged chromosomes, by their colocalization with the XY body in primary spermatocytes, and by male-limited sterility. Previously, we argued that such X-autosomal associations could interfere with meiotic sex chromosome inactivation. Recently, supporting evidence has reported modifications of histones in rearranged chromosomes by a process called the meiotic silencing of unsynapsed chromatin (MSUC). Here, we report on the transcriptional down-regulation of genes within the unsynapsed region of the rearranged mouse chromosome 17, and on the subsequent disturbance of X chromosome inactivation. The partial transcriptional suppression of genes in the unsynapsed chromatin was most prominent prior to the mid-pachytene stage of primary spermatocytes. Later, during the mid-late pachytene, the rearranged autosomes colocalized with the XY body, and the X chromosome failed to undergo proper transcriptional silencing. Our findings provide direct evidence on the MSUC acting at the mRNA level, and implicate that autosomal asynapsis in meiosis may cause male sterility by interfering with meiotic sex chromosome inactivation.

Crossover analysis using immunofluorescent detection of MLH1 foci in frozen–thawed testicular tissue

To date, the effects of freezing on spermatogenesis have not yet been fully investigated at a molecular level. Antibody localization studies have identified the MutL homolog 1 (MLH1) protein, a mis-match repair protein, at the prophase I stage of meiosis, which allows the detection of recombination foci during pachytene. This study investigated the effect of long-term testicular tissue cryopreservation on meiotic prophase I, identified by recombination foci frequency and synaptonemal complex (SC) integrity. Frozen-thawed testicular tissues from 12 males who had each fathered a child were used. Because vasectomy or reverse vasectomy procedures are rare in the locale of the investigation, it was not possible to obtain fresh testicular tissue and use the males as their own controls. Immunocytogenetic analysis of 612 spermatocytes at the pachytene stage was performed. The results indicated a mean number of MLH1 foci of 49.2 (SD +/- 5.9), and no correlation was found between the freezing period, the MLH1 frequency and the SC integrity. The results suggest that freezing of testicular tissue taken post-puberty does not appear to be detrimental to the crossover process as identified by occurrence of MLH1 loci.

Meiotic anomalies in infertile men with severe spermatogenic defects

BACKGROUND

This study was aimed at evaluating the rate of pairing failure in pachytene spermatocytes of patients presenting either an obstructive (O) or a non-obstructive (NO) infertility.

METHODS

Forty-one patients and 13 controls underwent testicular biopsy. Among the patients, 19 had an O infertility and 22 a NO infertility. Preparations of all patients and controls were Giemsa-stained, and synaptonemal complexes from nine of these patients and one control were immunostained.

RESULTS

In all, 2931 pachytene nuclei were analysed. The mean rate of asynapsed nuclei from the NO group (25.4%) was significantly higher than that of the O group (9.8%). There was no significant difference between the O group and the controls (10.6%). Immunocytochemistry showed that the number of pachytene nuclei decreased from the early to late pachytene sub-stage in all patients. Two NO patients, one azoospermic and one oligozoospermic, had a high percentage of asynapsed nuclei (86 and 91.8% respectively); one of these patients also presented a precocious localized separation of sister chromatids.

CONCLUSION

high levels of extended asynapsis could arise from a primary meiotic defect which may be responsible for 9% of the NO male infertilities at our centre. The prevalence of early pachytene substages suggests that the pachytene checkpoint is localized at the mid-pachytene stage in humans.

Meiotic studies in two human reciprocal translocations and their association with spermatogenic failure

BACKGROUND

Reciprocal translocations are often associated with infertility in male carriers. However, some carriers present normal semen profiles and are identified because of repetitive pregnancy failures.

METHODS

Here, we report two different cases of reciprocal translocations. The first patient carried a t(10;14) and was normozoospermic. The second patient carried a t(13;20) and was azoospermic. Synaptonemal complexes from both carriers were analysed using immunocytogenetic techniques and multi-centromere fluorescent in situ hybridization (cenM-FISH).

RESULTS

Associations between the quadrivalent and the sex body or other autosomes were seen only in the t(13;20) carrier. Heterosynapsis was observed only in the t(10;14) carrier. Synaptic pairing abnormalities were seen in 71% of the spreads in the t(13;20) carrier and 30% of the spreads in the t(10;14) carrier. Recombination frequency was decreased in the t(13;20) carrier, but not in the t(10;14) carrier.

CONCLUSIONS

By comparing these two different translocation carriers with different fertility outcomes, we discuss the possible mechanisms by which translocations might cause the spermatogenesis process to fail.