Rat Embryonic Fibroblasts (REF) are used to support the growth of rat and human pluripotent stem cells. REF not only provide a substrate for pluripotent stem cells to grow on, but also secrete critical growth factors to maintain stem cell pluripotency. REF are isolated from rat embryos and used at early passages. To serve as feeder cells, REF must be treated with mitomycin C or by irradiation to prevent cell proliferation. The treated cells can also be used to generate conditioned medium for feeder-free culture of pluripotent stem cells. REF from ScienCell Research Laboratories are isolated from embryonic day 14 CD® IGS rat embryos. These cells are cryopreserved at P0 and delivered frozen. Each vial contains 1 x 106 cells in 1 ml volume. REF are characterized by immunofluorescence with antibody specific to fibronectin. REF are negative for mycoplasma, bacteria, yeast, and fungi. REF are guaranteed to further expand for 5 population doublings under the conditions provided by ScienCell Research Laboratories. Recommended Medium It is recommended to use DMEM (Cat. #09221) supplemented with 10% fetal bovine serum (FBS, Cat. #0500) for culturing REF in vitro.