Mus musculus
MEFs were prepared from 3 independent mouse embryos of C57BL/6 mice at day 13.5 post coitum (E13.5). MEFs were co-transduced at passage-3 with a polycistronic vector expressing the 4 Yamanaka factors (Oct4, Sox2, Klf4, c-Myc and an mCherry reporter, Sommer et al., 2009) and the above-mentioned RNAi library co-expressing GFP. Four days after infection, double positive (GFP+/mCherry+) MEFs were FACS sorted and were reprogrammed for another 14 days towards the generation of iPSCs. Reprogrammed iPSCs that have silenced the transgene expression (mCherry-negative) and expressed SSEA1 (Expanded View 1A), which is a marker for pluripotent cells were considered for the study. To identify shRNAs that enhanced the reprogramming process we sorted reprogrammed cells (SSEA1+, mCherry-) as well as non-reprogrammed cells (SSEA1-, mCherry+).