tbx5a and tbx5b expression during early zebrafish development. tbx5b (A–H) is co-expressed with tbx5a in the developing eyes and heart whereas pectoral fin cells are uniquely labelled by tbx5a expression (A′–H′). Lateral views from the left side with anterior to the left are shown for 14 hpf (A–A′), 17 hpf (B–B′), 18 hpf (C–C′), 20 hpf (D–D′), 24 hpf (F–F′) and 27 hpf (G–G′) embryos. Dorsal views with anterior to the top are shown for 20 hpf embryos (E–E′), where expression of tbx5b (E) and tbx5a (E′) in the heart cone is better observed. Higher magnification of rostro-lateral views from the left of 27 hpf embryos (H–H′) are shown to emphasize the posterior-to-anterior gradient of expression pattern that tbx5b (H) and tbx5a (H′) exhibit. e, eye; h, heart; lpm, lateral plate mesoderm; pf, pectoral fin.

tbx5a and tbx5b expression during later stages of zebrafish development. tbx5b (A–L) is mainly co-expressed with tbx5a in the developing eyes and heart whereas pectoral fin cells only express tbx5a (A′–L′). Lateral views from the left side with anterior to the left are shown for 36 hpf (A–A′), 42 hpf (C–C′), 48 hpf (E–E′), 60 hpf (G–G′), 3 dpf (I–I′) and 4 dpf (K–K′) embryos. Detailed heart expression is better observed in ventral views with anterior to the top of 36 hpf (B–B′), 42 hpf (D–D′), 48 hpf (F–F′), 60 hpf (H–H′), 3 dpf (J–J′) and 4 dpf (L–L′) embryos. a, atrium; e, eye; pf, pectoral fin; v, ventricle.