Fig. 2. Whole-mount in situ hybridization of embryonic hearts with antisense riboprobe for VMHC1 (A-D), ET_A (E-I), ET_B (J-N) and ET_B2 (O-T), and with sense probe (insets in F-I). Whole embryos at E3-E3.5 (A,E,J,O) and whole hearts cut frontally into half at E6 (B,F,K,P), E10 (C,G,L,Q), E15 (H,M,S) and E18 (D,I,N) were examined. Purple staining represents positive hybridization signals. (R,T) High power views of the boxed area in Q and S, respectively. Arrows indicate ET_B2-signals in valve leaflets. ht, heart tube; at, atrium; rv, right ventricle; lv, left ventricle.