Fig. 4

Fig. 4. Ctr9, Cdc73, and Paf1 are required for AV boundary specification. (A–D) Cardiac expression of vmhc in 48 hpf embryos. In wild type (A), ctr9^LA961 mutant (B), cdc73 morphant (C), and paf1 morphant (D) embryos, vmhc expression is detected primarily in the ventricle. (E–H) Cardiac expression of amhc in 48 hpf embryos. In wild type (E), ctr9^LA961 mutant (F), cdc73 morphant (G), and paf1 morphant (H) embryos, amhc expression is detected primarily in the atrium. (I–L) Cardiac expression of bmp4 in 48 hpf embryos. In wild type embryos (I), bmp4 expression is detected in the myocardium of the ventricle, sinus venosus, and AV boundary (arrow). Ctr9^LA961 mutant (J), cdc73 morphant (K), and paf1 morphant (L) embryos display ventricular expression of bmp4, but have no discernable AV boundary expression. (M–P) Cardiac expression of tbx2b in 48 hpf embryos. In wild type embryos, tbx2b is expressed by the myocardium of the AV boundary (arrow, M). Ctr9^LA961 mutant (N), cdc73 morphant (O), and paf1 morphant (P) embryos instead aberrantly express tbx2b throughout the heart. (Q–T) Cardiac expression of notch1b in 48 hpf embryos. Notch1b is expressed by the AV boundary endocardium in wild type embryos (arrow, Q), but is not expressed in the hearts of ctr9^LA961 mutants (R), cdc73 morphants (S), and paf1 morphants (T).