Figure 5. ERK is activated during the first 4 hrs and is required for cardiogenesis over the same period.

(A) ERK is activated for at least 4 hours after conjugation of animal cap and anterior endoderm. Animal cap, anterior endoderm or AC/AE explants were collected at indicated times after conjugation and were subjected to Western analysis for doubly-phosphorylated ERK (dpERK) and total ERK. The latest time-point (St. 14) corresponds to 8–10 hours after conjugation. (B) U0126 treatment for the first 2 or 4 hours after conjugation effectively blocks ERK activation. (C) ERK activity is required during at least first four hours after conjugation for efficient cardiogenesis.