利用PRD-like同源域转录因子改善猪体细胞克隆胚异常基因组激活的研究

The low cloning efficiency limits the applications of somatic cell nuclear transfer technique in molecular breeding of the pig. Unfaithful zygotic genome activation (ZGA) in cloned embryos is one of the reasons for this deficiency. Recently, cloned embryo development has been improved in many species by the elimination of aberrant H3K9me3 deposition. However, we found that this method may not efficiently activate the zygotic genome in human and pig cloned embryos. Thus, we speculated that the insufficient expression of transcription factors was also responsible for the defects of ZGA initiation. In our RNA sequencing data, we found that PRD-like homeobox proteins were ZGA-related transcription factors with incomplete activation in cloned embryos. To detect the ZGA initiation in cloned embryos, we intend to utilize the DNA binding motif of PRD-like homeobox proteins to construct the ZGA reporter system, and insert this system in donor cell genome by CRISPR/Cas9 technique. Meanwhile, based on this system, we intend to use XIST knockout donor cell, remove H3K9me3 modification and supply PRD-like homeobox proteins in porcine cloned embryos, and evaluate the effect of these methods on ZGA initiation and embryo development. This research will advance the understanding of abnormal cloned ZGA from the point of internal defective transcription factors, and provide a more accurate approach to promoting cloned pig procreation.

克隆效率低下严重制约着体细胞克隆技术在猪分子育种领域的规模化应用，其原因之一是克隆胚存在异常的合子基因组激活（ZGA）。目前，已有研究通过清除H3K9me3修饰提高了多个物种的克隆效率，但我们发现该方法对人和猪克隆胚ZGA的调整作用有限，推测仍有缺失的关键转录因子致使ZGA出现启动异常。为此，项目前期从转录组数据里挖掘到克隆胚中表达不足的ZGA相关转录因子——PRD-like同源域家族蛋白，随后拟以其DNA结合基序构建报告系统，并通过CRISPR/Cas9技术将该系统插入供体细胞基因组，以此检测猪克隆胚ZGA的开启程度。另外，利用上述报告系统，项目拟进一步探索敲除XIST基因、清除H3K9me3修饰和补充PRD-like同源域转录因子对克隆胚ZGA启动及体内外发育的作用。本研究将从内源缺乏的转录因子这一角度丰富克隆胚ZGA异常的理论知识，同时为突破克隆猪的生产瓶颈提供改进方案。

克隆效率低下严重制约着体细胞克隆技术在分子设计育种和种质资源保存等生猪种业领域的规模化应用，其原因之一是克隆胚胎存在异常的合子基因组激活（ZGA），直接导致克隆胚胎在附植前发育阶段出现较高的发育阻滞率。项目前期推测仍有缺失的关键转录因子致使ZGA出现启动异常，并从转录组数据里挖掘到克隆胚胎中表达不足的ZGA相关转录因子——PRD-like同源域家族蛋白。基于该家族转录因子的DNA结合基序构建合子激活报告系统，申请人通过细胞转染实验鉴定到一个激活型的转录因子——LEUTX，并在克隆胚胎中显微注射其mRNA，最终发现注射LEUTX mRNA可以显著提高猪克隆胚胎的体外囊胚发育率近20%，并将克隆猪的出生效率由1.25%提高至4.42%，提升超过3.5倍。申请人还利用低细胞量的高通量测序技术，解析了LEUTX在胚胎ZGA阶段结合基因组的靶位点，确定LEUTX通过其C端招募组蛋白乙酰化转移酶，在靶位点建立组蛋白乙酰化H3K9ac、H3K18ac和H3K27ac等表观遗传修饰，最终促进胚胎ZGA正常启动。最后，申请人利用CRISPR/Cas9技术将上述合子激活报告系统插入供体细胞基因组Rosa26位点，以此细胞构建的克隆胚胎将能实时检测胚胎ZGA的开启程度并提前预知胚胎的发育命运，实现对猪优质克隆胚胎的早期筛选和精准移植。本研究从内源缺乏的转录因子这一角度丰富了克隆胚胎ZGA异常的理论知识，同时为突破克隆猪的生产瓶颈提供了切实有效的改进方案和细胞工具。