Synaptic configuration of quadrivalents and their association with the XY bivalent in spermatocytes of Robertsonian heterozygotes of Mus domesticus

BACKGROUND: The nuclear architecture of meiotic prophase spermatocytes is based on higher-order patterns of spatial associations among chromosomal domains and consequently is prone to modification by chromosomal rearrangements. We have shown that nuclear architecture is modified in spermatocytes of Robertsonian (Rb) homozygotes of Mus domesticus. In this study we analyse the synaptic configuration of the quadrivalents formed in the meiotic pro- phase of spermatocytes of mice double heterozygotes for the dependent Rb chromosomes: Rbs 11.16 and 16.17. RESULTS: Electron microscope spreads of 60 pachytene spermatocytes from four animals of Mus domesticus 2n = 38 were studied and their respective quadrivalents analysed in detail. Normal synaptonemal complex was found between arms 16 of the Rb metacentric chromosomes, telocentrics 11 and 17 and homologous arms of the Rb metacentric chromosomes. About 43% of the quadrivalents formed a synaptonemal complex between the heterologous short arms of chromosomes 11 and 17. This synaptonemal complex is bound to the nuclear envelope through a fourth synapsed telomere, thus dragging the entire quadrivalent to the nuclear envelope. About 57% of quadrivalents showed unsynapsed single axes in the short arms of the telocentric chromosomes. About 90% of these unsynapsed quadrivalents also showed a telomere-to-telomere association between one of the single axes of the telocentric chromosome 11 or 17 and the X chromosome single axis, which was otherwise normally paired with the Y chromosome. Nucleolar material was associated with two bivalents and with the quadrivalent. CONCLUSIONS: The spermatocytes of heterozygotes for dependent Rb chromosomes formed a quadrivalent where four chromosomes are synapsed together and bound to the nuclear envelope through four telomeres. The nuclear configuration is determined by the fourth shortest telomere, which drags the centromere regions and heterochromatin of all the chromosomes towards the nuclear envelope, favouring the reiterated encounter and eventual rearrangement between the heterologous chromosomes. The unsynapsed regions of quadrivalents are frequently bound to the single axis of the X chromosome, possibly perturbing chromatin condensation and gene expression.

Expression of synaptonemal complex protein 3 [SYCP3] m RNAin the testis: a molecular marker for spermatogenesis in azoospermic men

Men with unexplained infertility and azoospermia are often observed in the context of genetic defects. The expression of a wide variety of genes is developmentally regulated during human meiosis. Synaptonemal Protein 3 [SYCP3] gene, located on chromosome 12, encodes a DNA-binding protein as the structural component of the synaptonemal complex,which mediates the synopsis or homologous pairing of chromosomes during meiosis. Absence of SYCP3 in mice may lead to male infertility as well as female sub-fertility. SYCP3 expression analysis could be a tool for the prediction of human spermatogenesis progression, especially in infertile men. SYCP3 mRNA expression in testicular samples of 110 patients with non-obstructive azoospermia were studied in Avesina Infertility Clinic in Tehran, Iran during 2005 and early 2006. Semi-quantitative nested reverse transcriptase-PCR was employed in order to find the strength of gene expression. Using histopathological scoring for all samples, the expression level of SYCP3 during spermatogenesis was also evaluated. Testicular SYCP3 mRNA expression was observed in 67 patients [60.9%]. The expression level correlated with the degree of spermatogenic failure [p<0.0001]. While this gene had been expressed in patients with hypo-spermatogenesis and maturation arrest, a lack of expression was seen in those with spermatogonial arrest, Sertoli cell-only syndrome and testicular atrophy. These data indicate that SYCP3 is expressed in the human testis and it is restricted to germ cells. Our findings, in association with those obtained in experimental animals, show that lack of SYCP3 expression may have negative effects on spermatogenesis and male fertility. SYCP3 gene expression may help detect specific spermatogenesis stages in conjunction with histopathological findings