Figure 7.
Mutation of tmem2 causes ectopic AVC differentiation. (A–C, E–G) Whole-mount in situ hybridization indicates expression of AVC differentiation markers at 48 hpf. White dots outline the atrium (A) and ventricle (V). (A–C) Frontal views of wild-type embryos depict the restricted expression of the AVC endocardial marker notch1b (A) and the AVC myocardial markers bmp4 (B) and versican (C). (E–G) In contrast, tmem2 mutant embryos exhibit expanded expression of all three markers. (D,H) Immunofluorescence reveals localization of the endocardial cushion marker Dm-grasp at 48 hpf. (D) In wild-type embryos, Dm-grasp is found throughout the myocardium (outer layer), but is only found in the endocardium at the AVC (arrowheads). (H) In tmem2 mutants, Dm-grasp is found at the AVC (arrowheads), as well as throughout the ventricular endocardium. Adapted from Totong et al. (2011).