Paternally inherited H3K27me3 affects chromatin accessibility in mouse embryos produced by round spermatid injection

Abstract

Round spermatid injection (ROSI) results in a lower birth rate than intracytoplasmic sperm injection, which has hampered its clinical application. Inefficient development of ROSI-embryos has been attributed to epigenetic abnormalities. However, the chromatin-based mechanism that underpins the low birth rate in ROSI remains to be determined. Here, we show that a repressive histone mark H3K27me3 persists from mouse round spermatids into zygotes in ROSI and that round spermatid-derived H3K27me3 is associated with less accessible chromatin and impaired gene expression in ROSI-embryos. These loci are initially marked by H3K27me3 but undergo histone modification remodelling in spermiogenesis, resulting in reduced H3K27me3 in normal spermatozoa. Therefore, the absence of the epigenetic remodelling, presumably mediated by histone turnover during spermiogenesis, leads to dysregulation of chromatin accessibility and transcription in ROSI-embryos. Thus, our results unveil a molecular logic, in which chromatin states in round spermatids impinge on chromatin accessibility and transcription in ROSI-embryos, highlighting the importance of epigenetic remodelling during spermiogenesis in successful reproduction.

Nucleosomes in mammalian sperm: conveying paternal epigenetic inheritance or subject to reprogramming between generations?

“…Intriguingly, mouse embryos generated by injecting nuclei of round spermatids into oocytes (ROSI) have lower developmental rates than those injected with mature sperm nuclei (ICSI) [110] . ROSI-derived zygotes fail to demethylate paternal DNA and abnormally stain with H3K9me2/3 at paternal PCH 111 , 112 , 113•• . Moreover, sustained repression of certain genes in ROSI-derived 2-cell embryos correlates with higher promoter H3K27me3 in round spermatids compared to sperm [113] .…”

“…ROSI-derived zygotes fail to demethylate paternal DNA and abnormally stain with H3K9me2/3 at paternal PCH 111 , 112 , 113•• . Moreover, sustained repression of certain genes in ROSI-derived 2-cell embryos correlates with higher promoter H3K27me3 in round spermatids compared to sperm [113] . This finding possibly argues for round spermatid-derived H3K27me3 suppressing embryonic transcription and preventing the recruitment of epigenetic machineries normally reprogramming the paternal genome.…”

Estrogens alter epigenetic profile during male germ cell differentiation and histone-to-protamine exchange in mice

“…On the other hand, the overall impact of the sperm nucleus increased histone retention on sperm physiology, post-fertilization pronuclear formation/fusion, and early embryonic development may re ect the core histones and their PTMs total abundancies. At the same time it may also re ect a location among higher order nuclear architecture rather than their sequence-speci c genomic localization [38,41]. Therefore, the discovery and quantitative representation of the increased histone retention in the basal part of the sperm nucleus is critical output of this study (Fig.…”

Production of mouse offspring from zygotes fertilized with freeze-dried spermatids

“…Notably, although spermatids cannot fertilize oocytes by themselves, when spermatids are artificially injected into oocytes, healthy offspring can be obtained 13 , 14 . Despite the lower birth rates when this method is used than when mature spermatozoa are used 14 , 15 , spermatids are considered important components for preserving the genetic material of infertile or immature male animals 16 .…”