Selective advantage of euploid spermatocytes I in an azoospermic 47,XYY man with gonadal mosaicism

Although most XYY men have normal sperm counts and are fertile (supposedly due to the loss of the extra Y before meiosis), there is a minority who are infertile. In these cases, the XYY spermatocytes are able to enter meiosis and form different synaptic configurations. With regard to mosaics, there is scarce well-defined information on the presence of the second Y and its meiotic behaviour. In this study, the chromosome constitution and the synaptic behaviour of pachytene spermatocytes from an azoospermic man with testicular hypotrophy and non-mosaic 47,XYY karyotype were analysed. Furthermore, we determined the chromosome constitution of the somatic Sertoli cells. Five karyotypically normal men with obstructive azoospermia, but having complete spermatogenesis, were included as controls. Immuno-FISH using specific protein markers of synapsis and recombination (SYCP3, SYCP1, BRCA1, MLH1, CREST) and a specific Yq12 DNA probe were used. In addition, we used the newly developed Super-Resolution Structured Illumination Microscopy (SR-SIM) to clearly define the synaptic configurations. FISH analysis was also performed on Sertoli cells. The histopathological analysis showed variable degrees of spermatogenesis development in the testicular tissue of the propositus. Immuno-FISH analysis showed that most of the primary spermatocytes were euploid 46, XY. The use of SR-SIM confirmed the existence of this euploidy. Only a few pachytene spermatocytes showed an aneuploid X + YY constitution. Sertoli cells showed two different populations with one or two Y chromosomes, in similar proportions. Thus an abnormal niche of sex-trisomic Sertoli cells should be also considered when searching for the origin of spermatogenesis failure in XYY men.

The role of asynapsis in human spermatocyte failure

The basic molecular mechanisms by which chromosomal rearrangements in heterozygous state produce spermatogenic disturbances are poorly understood. Testicular biopsies from five patients - one carrier of a Robertsonian translocation rob t(13;14), two carriers of two different Y-autosome translocations, a t(Y;6) and a t(Y;11), one carrier of a reciprocal translocation t(3;13) and one carrier of a heterochromatin duplication in chromosome 9 - were processed for histopathological analysis, electron microscopy and fluorescent immunolocalization of meiotic proteins. In all the patients, the asynaptic regions during pachytene are labelled by BRCA1 and retained RAD51 foci. The variant histone γ-H2AX is located on the chromatin domains of the asynaptic regions and the XY body. In contrast, these meiotic proteins are absent in those chromosomal segments that are non-homologously synapsed. The present observations on five new cases and a review of recent studies show that the common features shared by all these cases are the abnormal location of some meiotic proteins and the presence of transcriptionally silenced chromatin domains on asynaptic regions. The frequent association of these silenced regions with the XY body and the rescue of spermatocyte viability through non-homologous synapsis are also shared by all these carriers. A passive, random mechanism of clustering of asynaptic regions with the XY body is suggested.

Focal spermatogenesis originates in euploid germ cells in classical Klinefelter patients

BACKGROUND

Klinefelter syndrome is the most frequent chromosome abnormality in human males. This paper aims to investigate the ploidy of meiotic and pre-meiotic germ cells found in spermatogenic foci, and furthermore, the sex chromosome constitution of Sertoli cells which surround these germ cells in non-mosaic Klinefelter patients.

METHODS AND RESULTS

A survey of 11 adult patients diagnosed with classical, non-mosaic Klinefelter syndrome who underwent testicular biopsies, showed that six of them had spermatogenesis foci. The topographical study of the biopsies showed that tubuli with germ cells are a minor fraction (8-24%) of all tubuli, although the overwhelming majority is devoid of germ cells. Using fluorescence in situ hybridization (FISH) with probes for the X-centromere and immunolocalization of meiotic proteins, the present work shows that all the 92 meiotic spermatocytes analyzed with FISH were euploid, 46,XY, and thus can form normal, haploid gametes. On the other hand, Sertoli cells show two marks for the X chromosome, meaning that they are 47,XXY.

CONCLUSIONS

These results provide a rationale for the high rate of success in the testicular sperm extraction plus ICSI procedures when applied to Klinefelter patients. It is also in agreement with previous studies in the XXY-mouse model. These spermatogenic foci most probably originate from clones of spermatogonia that have randomly lost one of the X chromosomes, probably during periods of life when high spermatogonial mitotic activity occurs.

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.

Synaptonemal complexes and XY behavior in two species of Argentinian armadillos: Chaetophractus villosus and Dasypus hybridus (Xenarthra, Dasypodidae)

Spermatocytes from the two armadillo species, C. villosus and D. hybridus were studied in microspreads for synaptonemal complexes (SCs) and in thin sections for electron microscopy (EM). The complete SC karyotype generally agrees with previous reports on mitotic chromosomes, except for the sex chromosomes. The X chromosome is submetacentric in both species and the Y is the shortest one in C. villosus and the second shortest in D. hybridus, and an extremely acrocentric one. A SC is formed along the total length of the Y chromosome, and this SC persists along all the pachytene substages. A single recombination nodule (RN) is located in the region of the SC nearest to the attachment to the nuclear envelope. The lateral element (LE) of the X axis in the SC shows a wavy aspect in most of the SC length distant from the nuclear envelope. Nucleoli are attached to acrocentric or submetacentric bivalents, are visibly double in some cells, and in thin sections show an elaborate nucleolonema. Some differences in the XY are species-specific, as the higher degree of tangling and stronger heteropycnosis in D. hybridus. The effective, single crossover of the XY pair is highly localized, despite the permanence of a long tract of SC.

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

BACKGROUND

The mechanisms of meiotic arrest in human spermatogenesis are poorly known.

METHODS AND RESULTS

A testicular biopsy from an azoospermic male showed complete spermatogenesis arrest at the spermatocyte stage, asynapsis, lack of formation of the XY body, partial reversion to a mitotic-like division and cell degeneration both at the prophase and at the abnormal cell divisions. Synaptonemal complex analysis showed minor segments of synapsis and mainly single axes. Fluorescent immunolocalization of meiotic proteins showed normal SYCP3, scarcity of SYCP1, null MLH1 foci, about 10 patches of gamma-H2AX, abnormal presence of BRCA1 among autosomal axes, absence of RAD51 in early and advanced spermatocytes and permanence of gamma-H2AX labelling up to the abnormal spermatocyte divisions that are the most advanced stage reached. There are at least six dominions of evenly packed chromatin resembling that of the normal XY body, but no true XY body.

CONCLUSIONS

The protein phenotype and the fine structure of the nuclei are compatible with a deficiency of the processing of double-strand DNA breaks in the zygotene-like spermatocytes, but the features of this defect do not agree with Spo11, Sycp1, Atm and Dmc1 null mutations, which give absence of XY body, synapsis disturbances and spermatocyte apoptosis in mice.

Changes in crossover distribution along a quadrivalent in a man carrier of a reciprocal translocation t(11;14)

A testicular biopsy from an infertile man carrying a heterozygous chromosome translocation t(11;14) was studied with synaptonemal complex analysis and immunolocalization of the protein MLH1 for crossover detection. A full blockage of spermatogenesis at the spermatocyte stage was related to the presence of the translocation quadrivalents at pachytene. Only 2% of the quadrivalents showed full synapsis. Most of the spermatocytes showed asynaptic free ends that frequently mingled with the XY pair. The average number of crossovers per cell was diminished from a mean of 52.7 in controls to a mean of 48 in the patient. The difference between the number of crossovers in the quadrivalent and the normal bivalents was highly significant. The distribution of crossovers over the segment of the quadrivalent corresponding to bivalent #14 was also very different from that of the control. It is concluded that in this translocation, the pattern of crossovers is changed, mainly due to a synaptic hindrance in the quadrivalent, and that the spermatogenesis arrest is mainly due to the quadrivalents that interact with the XY pair.