牛早期胚胎发育期间CHD1作用的分子机制

Decreasing fertility in dairy cows is one of the major challenges impacting the sustainable development of the dairy cow industry. Early embryo loss is one of the major factors results in infertility in dairy cows. During early embryonic development, various developmental events are reprogrammed to ensure the successful embryonic development, including chromatin remodeling. However, it remains largely unknown regarding the regulatory mechanisms of these critical developmental events. Previously, we identified that knockdown of CHD1 (Chromodomain Helicase DNA Binding Protein 1) reduced developmental potential of bovine early embryos and decreased the deposition of the critical histone variant H3.3 in bovine early embryos. However, the molecular mechanism underlying the CHD1’s effects in bovine early embryos is yet to be defined. The proposed studies will address 1) the intrinsic role of CHD1 and the underlying mechanism in chromatin remodeling and epigenetic reprogramming after fertilization, 2) if CHD1 regulates H3.3 deposition by modulating HIRA complex and 3) the role of CHD1, as a candidate reprogramming factor, in the development of somatic cell nuclear transfer embryos. The proposed research will increase our understanding of the molecular control of bovine early embryonic development and serve as the foundation on which future studies may be built to develop solutions to reduce early embryo loss or improving pregnancy rate in dairy cows.

奶牛繁殖率下降是影响奶牛养殖业平稳和可持续发展的主要问题之一。统计数据显示早期胚胎死亡是造成奶牛不孕的一个主要原因。早期胚胎发育阶段伴随着一系列重要的发育生物学事件的发生，如染色质重构等，但这些事件的调控机制尚未阐明。我们的前期研究发现染色质重构因子CHD1的缺失不仅造成牛早期胚胎发育率降低，还导致早期胚胎中重要的组蛋白变体H3.3的含量显著下降，但是其作用机制还不清楚。因此，本项目拟通过体外受精、显微注射siRNA等技术研究CHD1的缺失对牛早期胚胎中染色质组分、表观遗传修饰和H3.3伴侣蛋白HIRA复合物相关基因和蛋白的影响，揭示CHD1影响早期胚胎发育及调控H3.3的分子机制，并进一步探讨CHD1作为潜在的重编程因子在牛克隆胚胎发育过程中的作用和机制。本项目的研究将进一步加强我们对牛早期胚胎发育过程调控机制的理解，有助于采取相关措施提高奶牛早期胚胎的发育率，进而提高奶牛繁殖率。

奶牛繁殖率低一直是全球奶牛养殖业面临的严峻挑战之一。母牛每次发情后，第一次人工授精后的怀孕率约为40%，而高产奶牛的怀孕率更低。早期胚胎死亡是引起奶牛不孕的主要原因之一。近年来的研究显示约50%的胚胎死亡发生在受精后1个月内。而且，着床前后胚胎的死亡率高也是辅助生殖技术（例如：体外胚胎生产和体细胞克隆）效率低的原因之一。早期胚胎发育阶段发生一系列重要的发育生物学事件，如染色质重编程等，但这些生物学事件的调控机制尚未阐明。我们的前期研究发现染色质重构因子CHD1的缺失不仅造成牛早期胚胎发育率降低，还导致早期胚胎中重要的组蛋白变体H3.3的含量显著下降，但是其作用机制还不清楚。本项目以牛等哺乳动物早期胚胎为研究对象，系统研究了表观遗传调控因子CHD1及其相关因子在早期胚胎发育过程中的功能和机制，取得了以下主要成果：①揭示了CHD1和H3.3可能通过调控H3K36me2和H1的含量影响牛早期胚胎发育效率；②阐明了HIRA的敲低并不影响牛早期胚胎发育；③利用低细胞起始量ChIP-seq技术检测了H3K4me3在牛早期胚胎中的分布，并发现组蛋白甲基化修饰H3K4me3在多个物种胚胎基因组激活后剧烈下调；④发现了WDR5抑制早期胚胎中H3K4me3的建立；⑤建立了哺乳动物早期胚胎中RNA-seq体系，为CHD1的功能机制分析奠定基础；⑥建立了大动物基因编辑技术体系，为CHD1的功能分析提供候选手段，与Prather实验室同期在国际上率先获得抗传染性胃肠炎病毒基因编辑猪；⑦建立了早期胚胎中低细胞起始量的ChIP-seq技术体系，为下一步进行CHD1的分子机制研究奠定了基础。在The FASEB Journal、Biology of Reproduction、Epigenetics等主流SCI杂志发表论文6篇；培养博士生6名，硕士生3名。