Fig. S2.

Erk signaling is essential for the self-renewal of ESCs, demonstrated by an independent cell line, iErk2; Erk KO. (A) Experimental outline for the construction of iErk2; Erk KO ESCs. (B) Western blots demonstrate the diminishment of Erk expression and the expression dynamics of pluripotency factors in iErk2; Erk KO ESCs after Dox withdrawal. (C) Colony morphology change upon Erk KO. iErk2; Erk KO ESCs were continuously cultured in the absence of Dox for three passages. Phase-contrast images of ESC colonies at each passage are shown. (D) Reduced proliferation of ESCs after Erk KO. iErk2; Erk KO ESCs were cultured in serum/LIF medium with or without Dox. The cell numbers were counted every passage, and equal amounts of ESCs were plated onto tissue-culture dishes. (E and F) Expression dynamics of pluripotency (E) and differentiation markers (F) after Erk KO. iErk2; Erk KO ESCs were cultured as described in C. *P < 0.05; **P < 0.01. Error bars are SDs.