See ref. 1 for other necessary materials, such as cells, vectors and reagents.

Since the first report of mouse induced pluripotent stem (iPS) cells in 2006, questions have been raised regarding the method of retroviral transduction and the necessity of antibiotic selection, and various refinements have been made to the method of induction. The pluripotency of Nanog-GFP+ mouse iPS cells has been demonstrated to be sufficient to contribute to the germline in chimeric mice. Modification of plating density has also made it possible to induce iPS cells from wildtype mouse cells in the absence of antibiotic selection as well as by using only three factors, without t the oncogene c-Myc. In this protocol, we describe a method for the induction of pluripotency by gene transfection into mouse fibroblasts, as was previously detailed in ref. 1, with refinements to the previously published protocol shown in red letters