Figure 7: Suppression of MAP kinase signalling in miR-21 morphants and BDM-treated hearts.

(a–c) In the WT beating hearts, a phosphorylated form of Erk1/2 (pErk1/2) was stained in the cuboidal endocardial cells at the AV junction (yellow arrowheads in a). The entire endocardial cells were labelled by GFP, which expression was driven by the fli1 promoter (b,c). (d–f) In the miR-21 morphants, the pErk1/2 staining was week and the cells were flat. (g–i) When the heartbeat was stopped by BDM, phosphorylation of Erk1/2 was also suppressed, leaving only faint staining in the apical surface of flattened endocardial cells. (j–o) Injection of the miR-21 target protection MO and the U0126 treatment gave the same results on pErk1/s staining. A, atrium; V, ventricle. Scale bars, 20 μm.