Meiotic pairing and gene expression disturbance in germ cells from an infertile boar with a balanced reciprocal autosome-autosome translocation

Heat shock factor 5 establishes the male germ-line meiotic sex chromosome inactivation through regulation of Smarca4

Meiotic sex chromosome inactivation is an essential event in male germ cell development, which is directed by DNA damage response signaling independent of Xist RNA to silence the transcription activity of the sex chromosomes. However, the specific mechanism of establishment and maintenance of meiotic chromosome silencing is still unclear. Here we identify the HSF5 as a testicular specific protein and the expression of which was at the onset of meiosis pachytene stage to round sperm. When the function of the HSF5 was lost, meiosis sex chromosome remodeling and silencing fail, followed by activation of CHK2 checkpoint leads to germ cell apoptosis. Furthermore, we found that SMARCA4 in the linking the HSF5 to MSCI and uncover additional factors with meiotic sex chromosome remodeling. Together, our results demonstrate a requirement for HSF5 activity in spermatogenesis and suggest a role for the mammalian HSF5-SMARCA4 in programmed meiotic sex chromosome remodeling and silencing events that take place during meiosis.

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).

Cytogenetic Screening in Couples with Recurrent Pregnancy Loss: A Single-Center Study and Review of Literature

Context:

Recurrent pregnancy loss (RPL) is a devastating reproductive problem that affects more than 2% of couples who are trying to conceive. Chromosomal rearrangements in either carrier are a major cause of clinically recognized abortion.

Aims:

The purpose of this study is to report the prevalence of chromosome abnormalities in RPL and provide clinical characteristics of couples with two and more miscarriages.

Settings and Design:

Genetic counseling in laboratory of histology housed in a Faculty of Medicine of Sfax.

Materials and Methods:

Karyotype was generated from the peripheral blood lymphocyte cultures and the cytogenetic analysis was performed using R-bands after heat denaturation and Giemsa (RHG) banding. A multiplex polymerase chain reaction wherever necessary was done.

Statistical Analysis Used:

SPSS version 17.

Results:

A total of 104 couples with RPL were carried out in this study. The frequency of chromosomal rearrangements was 11.5%, three times more prevalent in men than women (P = 0.08). In addition, the prevalence of chromosomal anomalies increases according to the number of miscarriages (from 4.8% to 7.6%, with 2 or ≥3 miscarriages, respectively; P = 0.9). Finally, a particular familial adverse reproductive background was found in these carriers (P = 0.03).

Conclusions:

These data highlight that an RPL evaluation is appropriate after the second miscarriage and that cytogenetic evaluation is necessary for an accurate approach to elucidate the causes of RPL. Moreover, familial adverse reproductive backgrounds have an impact of being carrier of chromosome abnormalities and a larger study is mandatory to define reproductive characteristics of carriers.

Breeding and Economic Aspects of Cytogenetic Screening Studies of Pigs Qualified for Reproduction

Cytogenetic monitoring allows the identification and early removal of pigs affected by inherited karyotype defects from breeding herds. These abnormalities cause developmental anomalies, considerably reducing the fertility (by several dozen to 100%) and performance parameters of breeding herds, resulting in substantial financial losses. This mainly concerns reciprocal translocations, typical of pigs, which are highly prevalent (about 0.46%), generally occur de novo, and normally result in low breeding soundness of the carriers. Due to the potential spontaneous occurrence of chromosomal aberrations and the rapid spread of these genetic defects in the population, especially under artificial insemination conditions, it is necessary to perform routine karyotype screening of animals qualified for reproduction. The cytogenetic screening program for young boars, carried out using continually refined diagnostic techniques, permits a precise and reliable karyotype assessment, identification of chromosomal abnormalities, and formulation of specific selection guidelines.

Genetic defects in human azoospermia

As with many other diseases, genetic testing in human azoospermia was initially restricted to karyotype analyses (leading to diagnostic chromosome rearrangement tests for Klinefelter and other syndromes). With the advent of molecular biology in the 1980s, genetic screening was broadened to analyses of Y chromosome microdeletions and the gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR). Decades later, the emergence of whole-genome techniques has led to the identification of other genetic defects associated with human azoospermia. Although TEX11 and ADGRG2 defects are frequently described in men with azoospermia, most of the causal gene defects found to date are private (i.e. identified in a small number of consanguineous families).

Here, we provide an up-to-date overview of all the types of genetic defects known to be linked to human azoospermia and try to give clinical practice guidelines according to azoospermia phenotype. Along with homozygous mutations, polymorphisms and epigenetic defects are also briefly discussed. However, as these variations predispose to azoospermia, a specific review will be needed to compile data on all the particular genetic variations reported in the literature.

Meiotic behavior of a complex hexavalent in heterozygous mice for Robertsonian translocations: insights for synapsis dynamics

Natural populations of the house mouse Mus musculus domesticus show great diversity in chromosomal number due to the presence of chromosomal rearrangements, mainly Robertsonian translocations. Breeding between two populations with different chromosomal configurations generates subfertile or sterile hybrid individuals due to impaired meiotic development. In this study, we have analyzed prophase-I spermatocytes of hybrids formed by crossing mice from Vulcano and Lipari island populations. Both populations have a 2n = 26 karyotype but different combinations of Robertsonian translocations. We studied the progress of synapsis, recombination, and meiotic silencing of unsynapsed chromosomes during prophase-I through the immunolocalization of the proteins SYCP3, SYCP1, γH2AX, RAD51, and MLH1. In these hybrids, a hexavalent is formed that, depending on the degree of synapsis between chromosomes, can adopt an open chain, a ring, or a closed configuration. The frequency of these configurations varies throughout meiosis, with the maximum degree of synapsis occurring at mid pachytene. In addition, we observed the appearance of heterologous synapsis between telocentric and metacentric chromosomes; however, this synapsis seems to be transient and unstable and unsynapsed regions are frequently observed in mid-late pachytene. Interestingly, we found that chiasmata are frequently located at the boundaries of unsynapsed chromosomal regions in the hexavalent during late pachytene. These results provide new clues about synapsis dynamics during meiosis. We propose that mechanical forces generated along chromosomes may induce premature desynapsis, which, in turn, might be counteracted by the location of chiasmata. Despite these and additional meiotic features, such as the accumulation of γH2AX on unsynapsed chromosome regions, we observed a large number of cells that progressed to late stages of prophase-I, indicating that synapsis defects may not trigger a meiotic crisis in these hybrids.