Variations in cell morphology forming colonies 10–12 d after inducing reprogramming of mouse embryonic fibroblasts (MEFs). (A) Initial MEFs at the time of transfection. Note the cell density. (B) ES cell-like primary colony before picking. (C) The iPS cell culture after several passagings of clone in B. (D–I) Different non-ES cell-like colonies. After doxycycline withdrawal, they may stop growing or change to more ES cell-like morphology.