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

Nicolas Mary,Harmonie Barasc,Nathalie Bonnet,Alain Ducos,Alain Pinton,Anne Calgaro,Stéphane Ferchaud,Isabelle Raymond-Letron

doi:10.3390/genes12081137

Abstract

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).

Highlights

It is well known that abnormalities in chromosome pairing during the first meiotic division are associated with reduced fertility, in male mammals [1,2]
This meiotic silencing of unsynapsed chromatin (MSUC) [8] is characterized by the accumulation of BRCA1 and ATR recruited by SYCP3 and HORMAD1/2 on asynapsed regions, the spreading of ATR into the associated chromatin loops, and the phosphorylation of H2AX [4,5]
Results obtained for the more distal Bacterial Artificial Chromosome (BAC) probe located on the SSC1 (SBAB-91F6: 274,154,166–274,274,406 bp on the Sscrofa11.1) revealed that the breakpoint was located between the end of the BAC and the end of the chromosome (Figure 1b)

Summary

Introduction

It is well known that abnormalities in chromosome pairing during the first meiotic division (asynapsis) are associated with reduced fertility, in male mammals [1,2]. As proposed by Turner [7], this meiotic silencing consists of a chromatin remodeling process in which genes located along unsynapsed chromosomes are transcriptionally silenced during meiotic prophase I This meiotic silencing of unsynapsed chromatin (MSUC) [8] is characterized by the accumulation of BRCA1 and ATR recruited by SYCP3 and HORMAD1/2 on asynapsed regions, the spreading of ATR into the associated chromatin loops, and the phosphorylation of H2AX [4,5]. This phenomenon results from the signaling of asynapsis by some sensors (SYCP3, SMC1b, CDK2 HORMAD 1 and 2 and components of the BRCA1-A complex) and the genic inactivation by some effectors (e.g., MDC1, Senataxin AGO4, RAD18, HR6B and the variant histone H2AX) (Tuner, 2015). A DNA/RNA helicase involved in transcription regulation, RNA processing, and protection of the genome against oxidative damage, is essential for male meiosis, implicated in the process of meiotic sex chromosome inactivation (MSCI)

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