Rad51 is a key component of homologous recombination (HR) to repair DNA double-strand breaks and it forms Rad51 recombinase filaments of broken single-stranded DNA to promote HR. In addition to its role in DNA repair and cell cycle progression, Rad51 contributes to the reprogramming process during the generation of induced pluripotent stem cells. In light of this, we performed reprogramming experiments to examine the effect of co-expression of Rad51 and four reprogramming factors, Oct4, Sox2, Klf4, and c-Myc, on the reprogramming efficiency. Co-expression of Rad51 significantly increased the numbers of alkaline phosphatase-positive colonies and embryonic stem cell-like colonies during the process of reprogramming. Co-expression ofRad51 significantly increased the expression of epithelial markers at an early stage of reprogramming compared with control cells. Phosphorylated histone H2AX (γH2AX), which initiates the DNA double-strand break repair system, was highly accumulated in reprogramming intermediates upon co-expression of Rad51. This study identified a novel role of Rad51 in enhancing the reprogramming efficiency, possibly by facilitating mesenchymal-to-epithelial transition and by regulating a DNA damage repair pathway during the early phase of the reprogramming process.

INTRODUCTION
 MATERIALS AND METHODS
  1. Reprogramming of MEFs
  2. RNA extraction and real-time RT-PCR
  3. Protein extraction and immunoblotting
  4. Statistical analysis
 RESULTS AND DISCUSSION
 REFERENCES

• Jae-Young Lee(Dept. of Biomedical Science, College of Life Science, CHA University)
• Dae-Kwan Kim(Dept. of Biomedical Science, College of Life Science, CHA University)
• Jeong-Jae Ko(Dept. of Biomedical Science, College of Life Science, CHA University)
• Keun Pil Kim(Dept. of Life Science, Chung-Ang University) Corresponding Author
• Kyung-Soon Park(Dept. of Biomedical Science, College of Life Science, CHA University) Corresponding Author