The pLVRNAi vector and pCDH-MCS1-EF1-copGFP vector were purchased from Biosettia Inc. (Biosettia, San Diego, CA). The method of cloning the double-stranded shRNA sequence is described in the manufacturer's protocol. The siRNA oligonucleotide 59-CCGGCCCTCACTTCACTGCACTGTACTCGAGTA-CAGTGC AGTGAAGTGAGGGTTTTT-39 targeting human Oct-4 (NM_002701, nt 1035-1055) was synthesized and cloned into pLVRNAi to generate a lentiviral expression vector. The Oct-4 cDNA was amplified and purified by RT-PCR and cloned into a pCDH-MCS1-EF1-copGFP vector. Lentiviral production was done by transfection of 293T cells using Lipofectamine 2000 (LF2000, Invitrogen). Supernatants were collected 48 hours after transfection and then were filtered; the viral titers were then determined by FACS at 48 hours post-transduction. Subconfluent cells were infected with lentivirus at a multiplicity of infection of 5 in the presence of 8 ìg/ml polybrene (Sigma-Aldrich).