克隆胚胎早期发育过程中，染色质去凝集不彻底，来自体细胞的表观遗传修饰H3K9me3等擦除不完全，抑制胚胎基因组激活，导致克隆胚胎发育失败。分析高通量数据发现组蛋白伴侣CAF-1的亚基CHAF1b在牛和人克隆胚胎上异常高表达。而在诱导多能性干细胞上的研究显示CAF-1调控染色质凝集并阻遏重编程。我们前期研究发现敲降CHAF1b可提高组蛋白H3.3含量，降低染色质凝集状态的标志修饰H3K9me3的丰度，并提高牛克隆胚胎发育率，但其作用机制尚不清楚。本项目将通过体细胞核移植和显微注射等技术研究CHAF1b对牛克隆胚胎染色质组分、表观遗传修饰、染色质凝集状态、组蛋白H3.1-3.3置换、胚胎基因组激活和胚胎发育的影响，来探讨CHAF1b作为潜在的重编程抑制因子在牛克隆胚胎发育过程中的作用和机制。本项目的实施将为阐明体细胞克隆胚胎异常重编程的形成机制以及提高家畜克隆效率提供依据。

During early development of cloned embryos, chromatin disaggregation was incomplete, embryonic genome activation was suppressed by persisting epigenetic modification (E.g H3K9me3) of donor cell genome, which impeded embryonic development following somatic cell nuclear transfer (SCNT). Our and other recent study revealed that the expression level of histone chaperone chromatin assembly factor 1 (CAF-1) subunit CHAF1b in bovine and human nuclear transfer embryos was significantly higher than in vitro fertilization embryos. It has been reported that histone chaperone CAF-1 involves in chromatin condensation and safeguards somatic cell identity, which is an important obstacle to somatic reprogramming. CAF-1 markedly suppressed iPS cell formation. We found that knockdown of CHAF1b could increased the abundance of histone H3.3, decreased the abundance of histone H3K9me3, and increased the development rate of bovine SCNT blastocysts. However, the molecular mechanism underlying the CHAF1b's effects during reprogramming of bovine SCNT embryo remain incompletely understood. The proposed studies will address the role of CHAF1b and the mechanism regulating in chromatin remodeling and epigenetic reprogramming, chromatin agglutination, replacement of histone variant H3.1-3.3, embryonic genome activation, and embryonic development of the bovine SCNT embryos. This proposed research will provide new insights into revealing the mechanisms of aberrant reprogramming during SCNT and the cause of low cloning efficiency.