（通讯员 刘鑫 布国伟）近日，我校动物科学技术学院、动物医学院苗义良教授动物克隆与干细胞研究团队研究成果以“Coordination of zygotic genome activation entry and exit by H3K4me3 and H3K27me3 in porcine early embryos”在Genome Research发表。研究全面揭示了H3K4me3和H3K27me3在猪卵母细胞和受精胚胎发育过程中的动态分布规律，并首次证实了H3K4me3和H3K27me3参与调控猪受精胚胎合子基因组激活（ZGA）发生和退出的机制。
ZGA是动物早期胚胎发育过程中的核心事件，是实现母源-合子转换的关键，且不同物种ZGA的发生时期也有所不同。先前的研究已发现多个基因调控该事件的发生，而组蛋白修饰在该过程中同样发挥了重要的作用。
H3K4me3和H3K27me3在猪受精胚胎发育中的动态变化和功能研究
研究人员首先发现猪卵母细胞中的H3K4me3在ZGA基因启动子处呈现窄峰，受精后转变为宽峰，4细胞期后又转变为窄峰。在受精卵中同时敲低KDM5B和KDM5C（H3K4去甲基化酶基因）可在ZGA基因启动子上维持H3K4me3的宽峰分布，使ZGA基因无法激活表达，这说明H3K4me3在4细胞期的峰型转换调控着ZGA发生。
其次，研究人员还发现桑椹胚期重新建立的H3K27me3也会在ZGA基因启动子处富集，并与H3K4me3形成二元共价修饰。通过在胚胎培养液中添加GSK126（EZH2抑制剂）阻断H3K27me3的重建，发现ZGA基因在囊胚期的表达异常升高，这说明H3K4me3/H3K27me3共价状态在后期的建立有利于ZGA的退出。
最后，该团队还分析了猪体细胞克隆胚胎中H3K4me3和H3K27me3的分布情况，发现相比于受精胚胎，两种修饰在克隆胚胎4细胞期均存在严重的异常富集，而在囊胚期的富集差异较小，表明ZGA阶段组蛋白修饰的异常重编程仍是影响猪克隆胚胎发育的关键因素。
我校动物科学技术学院、动物医学院苗义良教授为论文的通讯作者，布国伟博士生、祝为博士后和刘鑫副研究员为论文的共同第一作者。该研究受到国家重点研发计划、国家自然科学基金、湖北省重点研发计划、湖北洪山实验室项目、华中农大校创基金等项目的资助。
【英文摘要】
Histone modifications are critical epigenetic indicators of chromatin state associated with gene expression. Although the reprogramming patterns of H3K4me3 and H3K27me3 have been elucidated in mouse and human preimplantation embryos, the relationship between these marks and zygotic genome activation (ZGA) remains poorly understood. By ultra-low-input native chromatin immunoprecipitation and sequencing, we profiled global H3K4me3 and H3K27me3 in porcine oocytes and in vitro fertilized (IVF) embryos. We found that promoters of ZGA genes occupied sharp H3K4me3 peaks in oocytes, and these peaks became broader after fertilization, and reshaped into sharp again during ZGA. By simultaneous depletion of H3K4me3 demethylase KDM5B and KDM5C, we determined that broad H3K4me3 domain maintenance impaired ZGA gene expression, suggesting its function to prevent premature ZGA entry. By contrast, broad H3K27me3 domains underwent global removal upon fertilization, followed by a re-establishment for H3K4me3/H3K27me3 bivalency in morulae. We also found that bivalent marks were deposited at promoters of ZGA genes, and inhibiting this deposition was correlated with the activation of ZGA genes. It suggests that promoter bivalency contributes to ZGA exit in porcine embryos. Moreover, we demonstrated that aberrant reprogramming of H3K4me3 and H3K27me3 triggered ZGA dysregulation in somatic cell nuclear transfer (SCNT) embryos, whereas H3K27me3-mediated imprinting did not exist in porcine IVF and SCNT embryos. Our findings highlight two previously unknown epigenetic reprogramming modes coordinated with ZGA in porcine preimplantation embryos. Finally, the similarities observed between porcine and human histone modification dynamics suggest that the porcine embryo may also be a useful model for human embryo research.
论文链接：https://genome.cshlp.org/content/early/2022/07/22/gr.276207.121
