猪母源关键多能因子的鉴定及其在体细胞重编程中的作用

Porcine iPS cell lines derived from the defined transcription factors (4-6) plus small molecular inhibitors and miRNA have been reported recently. However, the known porcine iPS cells were still not in the "Naive" stage, in which the gene epigenetic modifications were incomplete, and the porcine maternal pluripotency factors and signal pathways that maitained the pig iPS cell self-renewal were still unclear. The initial research showed that the key genes of Klf4 and Tbx2 from LIF pathway in mouse iPS cells were not up-regulated significantly in pig iPS cells, suggesting that the time and tissue specific expressions of pluripotent transcriptional factors were different among the animal species. The aims of this project are to screen the porcine specific pluripotency factors from GV stage oocytes and 4/8-cell stage embryos by the high-throughput sequencing, bioinformatics analysis, and gene expression and regulation analysis in vitro and in vivo. Through setting up a porcine early stage embryo transcriptome database, we expect to find out the key porcine transcriptional factors and the related signaling pathway, and apply the new porcine specific factor for the cell reprogramming to generate the naive type porcine iPS cell line. This investigation may provide novel means to conduct the application of iPS technology in animal cell reprogramming studies.

已报道的猪iPS细胞与"原始态（Naive）"的多能干细胞仍有一定差距，其中原因之一是调控猪体细胞重编程的关键多能因子和维持猪iPS细胞自我更新的调控网络仍不清楚。例如，我们发现在小鼠iPS细胞起关键作用的LIF通路中的Klf4和Tbx2基因，在猪iPS细胞中没有显著上调，表明不同物种间多能转录因子的时空表达和调控存在差异。卵母细胞携带大量母源性转录因子，对激活和维持多能干细胞自我更新能力起着重要调控作用。本研究拟通过高通量测序、生物信息分析、基因表达和调控等相关技术手段，对猪成熟卵母细胞（MII期）基因转录组进行测定，鉴定猪母源关键多能转录因子，探明其表观遗传修饰和信号通路的调控规律。对新发现的因子进行体内外功能验证，并用新因子辅助猪iPS细胞的诱导，从而促进建立Naive 状态猪iPS细胞系的效率，使iPS技术能够有效用于哺乳动物细胞重编程研究。

目前报道的猪iPS细胞与始发态（Naïve）多能干细胞仍有一定差距，其中原因之一是调控猪体细胞重编程的关键多能因子和维持猪iPS细胞自我更新的调控网络仍不清楚。因此，本课题对猪多能干细胞和早期胚胎进行测序，建立猪卵母细胞转录组数据库，并对mRNAs和miRNAs组学进行分析和注释。系统分析了母源因子OCT4、SOX2、NANOG和合子激活因子ESRRB、SALL4、EpCAM、OTX2等基因的表达调控特性，及其在猪细胞重编程过程中的作用。通过揭示猪多能性因子与维持胚层分化信号（包括LIF、bFGF、BMP、TGF-beta、Wnt/EpCAM等）通路之间的相互调节关系，发现在猪细胞重编程的诱导起始阶段，LIF和b-FGF信号通路是必须的，但是，在维持细胞多能性阶段可以不依赖于LIF和b-FGF，这两个信号通路可以被小分子抑制剂替代。我们据此提出了全新的两步法诱导猪细胞重编程策略。我们还通过筛选，建立了全新的3i培养体系。猪DOX-iPS细胞在不添加Dox的3i培养液中可以长期传代，并保持多能性状态，将3i培养体系用于培养不同实验室来源的猪iPS和ES细胞，都获得了较好的效果。配合两步法诱导策略，用新的3i培养体系和多能因子进行猪iPS细胞的诱导，从而达到促进建立Naïve 状态猪iPS细胞建系的效率。