1. Stem Cell Niche Division, Research Institute, Modern Cell and Tissue Technologies, Gongneung2dong, Nowon-gu, Seoul 139-743, Korea
2. Research Institute of Molecular Genetics, School of Life Sciences and Biotechnology, Korea University, Anam-Dong, Seoungbuk-Gu, Seoul 136-710, Korea
3. Department of Pediatric dentistry, College of Dentistry, Won-kwang University 1142 San-bon Dong, Gun-po city, Kyung-gi Do 435-040, Korea
4. Bute Medical School, University of St Andrews, Westburn Lane, St Andrews, Fife, KY16 9TS, UK
5. Laboratory of Stem Cell Research, CEFO Co. Ltd, 46-21 Susongdong, Jongno-gu, Seoul 110-140, South Korea