Es grade fbs

The murine G1ER cell line was kindly provided by Drs. Mitchell Weiss and Stuart Orkin.^{38 (link)–40 (link)} Cells were maintained between 1 × 10⁵ and 2 × 10⁶ cells/mL by dilution into fresh medium or by centrifuging the cells at 125 g × 5 min and resuspending in fresh medium. G1ER cells were cultured in media containing 500 mL Iscove’s MDM (Gibco, 12440053), 75 mL ES-grade FBS (Gibco, 16141079), 10 mL penicillin/streptomycin stock (Gibco 15140122), 6.2 μL monothioglycerol (MTG) (Sigma, M6145), 100 μL erythropoietin (Procrit, 10,000 U/mL stock), and 50 μL puromycin (InvivoGen, ant-pr; ~1 μg/mL). Fresh mouse stem cell factor was added when passaging cells at 20 ng / mL with a 1000X dilution (Sigma S9915, resuspended in 0.8X PBS).

E14 ESCs were cultured in DMEM with 15% ES-grade FBS (Gibco) and 1000 U/mL LIF (Millipore) or under standard 2i conditions. NIH3T3 cells were cultured in DMEM with 10% FBS. For colony formation assay, cells were seeded at a density of 1 × 10³ cells per 10-cm plate. Colonies were fixed and stained with 0.02% Crystal violet. Stained colonies were first photographed and then extracted in 1% SDS solution and quantified at 570 nm. For the cell viability assay (MTT), cells were seeded in 96-well plates at a density of 3000 cells per well. MTT solution was added to the cells at a final concentration of 0.5 mg/mL, and cells were incubated at 37°C before quantification.