Histone methylation regulates gene expression in the round spermatids to set the RNA payloads of sperm

Gene expression during spermatogenesis undergoes significant changes due to a demanding sequence of mitosis, meiosis and differentiation. Round spermatids have to prepare for DNA condensation as well as synthesize transcripts of genes required for the differentiation process. However, the mechanisms of gene activation and silencing in round spermatids remain largely unknown. We employed ChIP-seq to figure out the correlation of H3K4me3 and H3K9me3 marks with transcriptional activation and silencing in round spermatids. Out of about 2800 genes identified by H3K4me3 chipseq, transcriptome sequencing in purified round spermatids showed the presence of transcripts corresponding to about 64% of the genes. On the other hand, only about 25% of H3K9me3 enriched genes showed transcription in round spermatids, that too at very low levels. In conclusion, H3K4me3 enrichment in round spermatids correlates significantly with gene expression and H3K9me3 correlates with gene silencing, both of which are equally important for successful spermatogenesis.精子发生过程中的基因表达会发生显著动态变化，这源于其包含一系列严苛有序的有丝分裂、减数分裂与分化过程。圆形精子细胞需要为DNA浓缩做好准备，同时合成分化过程所需基因的转录本。然而，目前圆形精子细胞中基因激活与沉默的调控机制仍未完全明确。本研究采用染色质免疫共沉淀测序（ChIP-seq）技术，探究了圆形精子细胞中组蛋白H3赖氨酸4三甲基化（H3K4me3）与组蛋白H3赖氨酸9三甲基化（H3K9me3）修饰与转录激活、沉默之间的关联。在通过H3K4me3 ChIP-seq鉴定得到的约2800个基因中，对纯化后的圆形精子细胞进行转录组测序后发现，其中约64%的基因存在对应转录本。与之相对，富集H3K9me3修饰的基因中，仅有约25%在圆形精子细胞中存在转录现象，且其转录水平极低。综上，圆形精子细胞中H3K4me3富集与基因表达显著相关，而H3K9me3则与基因沉默密切相关，二者对于精子发生的顺利完成均具有同等重要的作用。