Fig. 8. Restoring wild-type endoderm in cas mutants allows heart fusion. (A-C) nkx2.5 and fkd7 expression were detected by in situ hybridisation in 24 hpf embryos. (A) Wild-type embryo, (B) control cas embryo, (C) and cas embryo grafted with wild-type activated cells. Arrowheads indicate the heart in wild-type embryos, hemicardia in cas and fused hemicardia in grafted cas embryos. (D-F) Transverse sections through the heart region of 24 hpf embryos stained for nkx2.5 expression. (D) Wild-type embryo with a single heart. (E) Control cas embryo with two hemicardia in lateral position. (F) cas embryo grafted with wild-type activated cells. The two hemicardia have fused at the midline. The inset is a close-up view of the heart region showing that grafted cells (brown nuclei) are not incorporated into the heart but are endodermal derivatives overlaying it. (G-H) cas embryos grafted with wild-type activated cells exhibiting an axis duplication. Arrowheads point to the unfused hemicardia in the primary axis (H) and the arrow indicates the heart in the secondary axis (G, H). (G) Lateral view of a live embryo, anterior left. (H) Ventral view, following staining for nkx2.5 expression. nt, nerve tube.
