HeLa, HEK293T and NIH3T3 cells were cultured in DMEM with 10% inactivated FBS, 1% Penn/Strep, 1% Glutamine, 1% non-essential amino acids. Transfection was done using Fugene HD (Promega) using a 2:6 ratio (a total DNA amount of 2 μg and 6 μl of Fugene HD reagent) in 6-well plates. For TetO::tdTomato experiment, 2 μg of the chimeric vector was used. For endogenous gene activation experiments, the U6 promoter-sgRNA-terminator sequence was amplified from the PBneo-sgRNA plasmids, purified by PCR purification kit (QIAGEN), and transfected as linear DNA (1 μg Total sgRNA expressing DNA) with 1 μg of pmax-dCas9VP160 plasmid. When there are multiple sgRNAs for multiple genes, the amount per sgRNA was evenly divided among genes first, then among the sgRNAs targeting each gene.