Murine embryonic fibroblasts (MEFs) were isolated from mouse embryos of CF-1 strain (Harlan Laboratories, Inc.) harvested at 12.5–13.5 postcoitum (p.c.). Briefly, embryos were dissected out of terminally anesthetized mice. The head and internal organs were removed, and the remaining carcasses were finely minced, trypsinized into single-cell suspensions, and plated onto T75 flasks. The cultured MEFs (P0) were frozen or expanded for up to 3 times (P3) before they were used for experiments.
