Fig. 4.

Loss of Erk signaling leads to G1 cell-cycle arrest and apoptosis of ESCs. (A) Cell-cycle analysis of iErk1; Erk KO ESCs at different passages after Dox withdrawal. (B) p38 is activated upon Erk KO. The expression of p38 and p-p38 in iErk1; Erk KO ESCs at different passages after Dox withdrawal was determined by Western blot. (C and D) Inhibition of p38 suppresses ESC apoptosis induced by Erk KO. iErk1; Erk KO ESCs were cultured in the absence of Dox for two passages, with or without the p38 inhibitor SB203580. (C) Expression of p38 and p-p38 in Erk KO ESCs treated with or without SB203580 (SB). (D) Cell-cycle analysis was performed with these cells. (A and D) Percentages of sub-G1 cells in total cells (in bold and underlined) and percentages of G1, S, and G2/M cells in nonapoptotic cells are shown.