体外重编程会造成DNA双链断裂，因此诱导型多功能干细胞（iPSC）的基因组中会发生高频率的简单核苷酸变异（SNVs）。我们前期发现重编程可激活Δ133p53表达，Δ133p53通过抑制细胞凋亡来提高重编程频率，同时又可以通过促进DNA双链断裂修复来维持遗传稳定性。近期我们将过表达Δ133p53所获得的iPSC克隆进行全基因组测序意外发现，Δ133p53特异性显著降低全基因组的编码区SNVs。鉴于编码区的重要性，那么体内是否存在着编码区DNA双链断裂优先采用同源重组修复（HR）呢？此研究将阐明：.1. 编码区和非编码区DNA双链断裂是否存在着HR修复的差异；.2. ∆133p53特异性降低iPSC编码区SNVs的分子机制；.3. 有机体水平上，探讨斑马鱼∆113p53以及参与选择性修复的基因在维持编码区稳定性中的作用。

Induced Pluripotent Stem cells (iPSCs) have great potential in regenerative medicine, but this depends on the integrity of their genomes. A number of studies have shown that the reprogramming process can induce genetic abnormalities in human iPSCs. The most possible reason for generation of genetic variants in iPSCs is that early reprogramming of iPSCs generates DNA double-stand breaks (DSBs). DNA DSBs are the most catastrophic forms of genotoxic insult a cell can encounter. Improper repair of such damage results in genomic instability which predisposes an organism to immunodeficiency, neurological damage and cancer. As such, organisms have evolved three efficient systems to repair such damage. They are Homologous Recombination (HR), Non-Homologous End Joining (NHEJ) and Single Strand Annealing (SSA) pathways. While NHEJ and SSA promote the potentially inaccurate relegation of DSBs, HR precisely restores the genomic sequence of the broken DNA ends by utilizing sister chromatids as template for repair..A central part of the DNA damage response is the activation of the tumour repressor p53 resulting in cell cycle arrest, DNA damage repair, apoptosis, or senescense to provide genome stability. p53 has been reported to inhibit DNA double-strand break (DSB) repair pathways. However, Δ133p53, an N-terminal truncated isoform of p53, a p53 target gene, not only functions to inhibit p53 apoptotic activity, but also promotes DNA DSB repair pathways to protect cells from death and DNA damages upon DNA DSBs..p53 plays a dual role in iPSC reprogramming. The DNA damage response in early reprogramming activates p53. The activated p53 prevents the reprogramming of cells carrying various types of DNA damage by promoting apoptosis and senescence of these cells. Although the knockdown of p53 allows high reprogramming efficiency, the generated iPSCs have a high risk of carrying DNA aberrations. .Our recent study demonstrates that Δ133p53 is also induced in iPSC reprogramming. The expression of Δ133p53 during reprogramming not only increases reprogramming efficiency by its anti-apoptotic activity, but also reduces the chromosomal aberrations by promoting DNA DSB repair. To further investigate whether the overexpression of Δ133p53 can improve the genetic quality of the resultant iPSCs, a whole-genome sequencing approach was applied. A total of ten independent reprogrammed iPSC clones at passage four (including 5 iPSC lines induced by 4 Yamanaka factors and five iPSC lines induced by the co-expression of 4 Yamanaka factors and Δ133p53) and the parental CDD-1079sk cell line have been subjected to whole-genome sequencing with an Illumina Hiseq Xten sequencer. When compared to the human reference genome sequence (hg19), we identified approximately 3.0-4.2 million Single nucleotide variants (SNVs including SNPs and Indels) in each of the iPSC lines as well as in their parental CDD-1079sk cells. The total and de novo SNVs were only slightly decreased in the iPSCs with overexpression of Δ133p53, compared to the iPSCs induced with Yamanaka 4 factors only. Strikingly, the total and de novo SNVs in coding region were significantly reduced by the expression of Δ133p53. .Single SNV in coding regions may lead complete loss of function in the encoded protein. However, the chance for SNVs in non-coding regions to completely change the gene function is not as high as those in coding regions. Thus, it raises an important scientific question: does Δ133p53 promote cell to preferentially repair DNA DSBs in coding region with HR pathway? The aims of this project are as follow: .1. To determine whether HR pathway is encoded for preferentially repairing DNA DSBs in coding region; .2. To explore the molecular mechanisms for Δ133p53 to specifically reduce the SNVs in coding region of iPSCs;.3. At organism level, to investigate the roles of Δ113p53 and genes related for recruitment of HR to coding region on zebrafish genetic stability.