An oligonucleotide containing a stem-loop structure targeting the Oct-4 gene was designed using the RNAi program (http://athena. bioc.uvic.ca/). The targeted sequence was GCGAACCAGTATC-GAGAAC in the Oct-4/POU5F1 gene (515,534 nt; accession no. NM_203289). This sequence was first cloned into a pBS/U6 vector. Then the U6-RNAi cassette was subcloned into a lentiviral vector, pFUGW [26] , and the sequences were verified by DNA sequencing. 