Deficiency of the multi-copy mouse Y gene Sly causes sperm DNA damage and abnormal chromatin packaging

Abstract

SummaryIn mouse and man Y chromosome deletions are frequently associated with spermatogenic defects. Mice with extensive deletions of nonpairing Y chromosome long arm (NPYq) are infertile and produce sperm with grossly misshapen heads, abnormal chromatin packaging and DNA damage. The NPYq-encoded multi-copy gene Sly controls the expression of sex chromosome genes after meiosis and Sly deficiency results in a remarkable upregulation of sex chromosome genes. Sly deficiency has been shown to be the underlying cause of the sperm head anomalies and infertility associated with NPYq gene loss, but it was not known whether it recapitulates sperm DNA damage phenotype. We produced and examined mice with transgenically (RNAi) silenced Sly and demonstrated that these mice have increased incidence of sperm with DNA damage and poorly condensed and insufficiently protaminated chromatin. We also investigated the contribution of each of the two Sly-encoded transcript variants and noted that the phenotype was only observed when both variants were knocked down, and that the phenotype was intermediate in severity compared with mice with severe NPYq deficiency. Our data demonstrate that Sly deficiency is responsible for the sperm DNA damage/chromatin packaging defects observed in mice with NPYq deletions and point to SLY proteins involvement in chromatin reprogramming during spermiogenesis, probably through their effect on the post-meiotic expression of spermiogenic genes. Considering the importance of the sperm epigenome for embryonic and fetal development and the possibility of its inter-generational transmission, our results are important for future investigations of the molecular mechanisms of this biologically and clinically important process.

Functional significance of the sex chromosomes during spermatogenesis

“…With the exception of the male sex-determining gene, Sry , surviving ancestral Y-linked single-copy genes are broadly expressed, both in the adult and throughout development (Bellott, et al 2014). In contrast, ampliconic/multi-copy genes on the sex chromosomes tend to be expressed specifically in male germ cells, with potential roles in postmeiotic spermatids (Cocquet, et al 2010, Comptour, et al 2014, Mueller, et al 2008, Mueller, et al 2013, Reynard, et al 2009, Riel, et al 2013, Sin, et al 2012b). In this section, we provide examples of single-copy and ampliconic/multi-copy genes from mouse genetic studies in the regulation of spermatogenesis.…”

“…Its long arm contains the highly amplified germ cell-specific gene families Sly , Srsy , and Ssty , all of which were acquired during the evolution of the rodent lineage (Soh, et al 2014). Mice lacking part or all of the long-arm genes show mild-to-severe defects in sperm morphology, fertilization, and fertility (Burgoyne, et al 1992, Conway, et al 1994, Riel, et al 2013, Suh, et al 1989, Toure, et al 2004b). On the short arm, Eif2s3y is the sole factor essential for spermatogonial proliferation (Mazeyrat, et al 2001).…”

“…Using a shRNA transgene to knock down Sly , mice exhibited sperm head abnormalities and reduced fertility (Cocquet, et al 2009). In addition, knockdown of Sly also leads to sperm DNA damage and defective chromatin packaging (Riel, et al 2013). Interestingly, SLY protein accumulates on PMSC, and Sly knockdown causes derepression of sex-linked genes in spermatids, suggesting that Sly escapes postmeiotic silencing to regulate PMSC (Cocquet, et al 2009).…”

Differential sperm motility mediates the sex ratio drive shaping mouse sex chromosome evolution

“…As yet, the root cause of the skewing remains unknown. However, it is known to be regulated by a conflict between the sex-linked ampliconic transcriptional regulators Slx and Sly in haploid spermatids [8][9][10][11][12]. The prevailing model is that one or more X-linked genes acts post-meiotically to favour the production of female offspring, and that these genes in turn are repressed by (Y-linked) Sly and activated by (X-linked) Slx.…”

SSTY proteins co‐localize with the post‐meiotic sex chromatin and interact with regulators of its expression

“…Importantly, males without the MSYq region exhibit more severe sperm defects than Sly-deficient males, associated with a higher de-repression of XY genes and loss of additional epigenetic marks [24][25][26][27]. This difference may be due to insufficient knockdown of Sly, but we have observed that limited SLY protein remains in Sly-deficient males [25] (J.C. MAW, unpublished data); it is therefore more likely that another MSYq gene contributes to the regulation of post-meiotic sex chromosome gene expression.…”