Figure 1.

Differentiation of MEKK1−/− ES cells into cardiac myocytes. (a) Hoechst 33258 DNA staining of the cluster of MEKK1−/− ESCM after Zeocin selection (Left). Anti-sarcomeric myosin immunofluorescence with MF 20 of the same field (Right). (b) Ultrastructural analysis of selected MEKK1−/− ESCM. S, sarcomere; I, intercalated disc; G, gap junction. (c) Changes in contracting rate of ESCM in response to isoproterenol. Open and solid bars indicate wild-type and MEKK1−/− ESCM (n = 10, each), respectively. * and # indicate significant differences (P < 0.05) from the values at corresponding control and at treatment with 0.1 μM isoproterenol, respectively.