Epigenetic abnormalities of the mouse paternal zygotic genome associated with microinsemination of round spermatids.

Although round spermatid injection can be used to create progeny for males who do not produce mature sperm, the rate of successful embryogenesis after such procedures is significantly lower than that for similar procedures using mature spermatozoa. The mechanisms underlying this difference are unknown. In this study, we demonstrate that, unlike the normal paternal genome, the paternal zygotic genome derived from a round spermatid is highly remethylated before first mitosis after demethylation. Genomes from elongated spermatids exhibited an intermediate level of DNA methylation, between those of round spermatids and mature spermatozoa, suggesting that the male germ cell acquires the ability to maintain its undermethylated state in the paternal zygotic genome during this phase of spermiogenesis. In addition, treatment of zygotes with trichostatin A led to a significant reduction in DNA methylation, specifically in the spermatid-derived paternal genome, except for the pericentromeric regions enriched by trimethylation of Lys9 of histone H3. These data provide insight into epigenetic errors that may be associated with the poor development of embryos generated from immature spermatozoa.