Dynamic Change of R-Loop Implicates in the Regulation of Zygotic Genome Activation in Mouse.

In mice, zygotic genome activation (ZGA) occurs in two steps: minor ZGA at the one-cell stage and major ZGA at the two-cell stage. Regarding the regulation of gene transcription, minor ZGA is known to have unique features, including a transcriptionally permissive state of chromatin and insufficient splicing processes. The molecular characteristics may originate from extremely open chromatin states in the one-cell stage zygotes, yet the precise underlying mechanism has not been well studied. Recently, the R-loop, a triple-stranded nucleic acid structure of the DNA/RNA hybrid, has been implicated in gene transcription and DNA replication. Therefore, in the present study, we examined the changes in R-loop dynamics during mouse zygotic development, and its roles in zygotic transcription or DNA replication. Our analysis revealed that R-loops persist in the genome of metaphase II oocytes and preimplantation embryos from the zygote to the blastocyst stage. In particular, zygotic R-loop levels dynamically change as development proceeds, showing that R-loop levels decrease as pronucleus maturation occurs. Mechanistically, R-loop dynamics are likely linked to ZGA, as inhibition of either DNA replication or transcription at the time of minor ZGA decreases R-loop levels in the pronuclei of zygotes. However, the induction of DNA damage by treatment with anticancer agents, including cisplatin or doxorubicin, does not elicit genome-wide changes in zygotic R-loop levels. Therefore, our study suggests that R-loop formation is mechanistically associated with the regulation of mouse ZGA, especially minor ZGA, by modulating gene transcription and DNA replication.

RNA sequencing data of mouse 2-cell embryos treated with DMSO.

To understand the effect of DMSO in preimplantation embryos, we have treated mouse 1 cell zygotes with DMSO and found that DMSO treatment caused 2 or 4 cell embryonic arrest and altered the acetylation levels of mouse preimplantation embryos To illustrate the mechanism of DMSO in mouse preimplantation embryos, fertilized zygotes have been treated with 2% of DMSO and then performed RNA-seq analyses. Differentially expressed genes were identified using DESeq2 after adjustment for false discovery rate (FDR q value < 0.05). Gene Set Enrichment Analysis (GSEA) was also performed to identify biological pathways significantly modulated by DMSO. Raw and processed RNA-seq data were deposited and made publicly available on the Gene Expression Omnibus (GEO; GSE124598). The data presented in this article are related to the research paper entitled "DMSO impairs the transcriptional program for maternal-to-embryonic transition by altering histone acetylation", available in Biomaterials [1].

DMSO impairs the transcriptional program for maternal-to-embryonic transition by altering histone acetylation.

Dimethyl sulfoxide (DMSO) is widely used in basic and clinical research, yet its toxicity and biocompatibility properties remain elusive. Here, we report that exposure of mouse zygotes to 2% DMSO perturbed the transcriptional program, critical for maternal-to-embryonic transition and provoked developmental arrest at the 2- or 4-cell stage. Mechanistically, DMSO decreased total protein acetylation in the 2-cell embryos but increased histone H3 and H4 acetylations, as well as p53, H3K9, and H3K27 acetylations. The epigenetic changes led to an altered expression pattern of 16.26% of total valid genes in DMSO-exposed embryos. Among the affected genes, expression of maternal and minor zygotic gene activation (ZGA) genes was enhanced, whereas the ubiquitin-proteasome system, major ZGA transcripts, embryonic gene activation, the cell cycle, and ribosomal biogenesis genes were suppressed. Therefore, we conclude that DMSO causes developmental arrest by disrupting maternal-to-embryonic transition; hence, caution should be exerted when using it as a solvent.