Fig. 6.

Dorsal GATA4-expressing transplants show a Dkk-1 sensitive delay of cardiogenesis. (A, A′) Control transplants of GATA4-injected reaggregates (CAG-GFP) showed cardiac differentiation by GFP expression at stage 37 as indicated by the arrows. (B, B′) In contrast, transplants placed in the dorsal side of the host (position 6 in Fig. 5A) were negative for GFP expression at stage 37 (100%; n = 20), but 50% were positive after stage 39 (C, C′). No beating activity was detected in these reaggregates. (D, D′) Double-WMISH showed that 20% (n = 94) of dorsal transplants express myl7 alone (white arrowhead) and only a small group of cells express both myl7 and myl3 (black arrowhead). (E–F′) Both control and dorsal transplants of reaggregates (CAG-GFP) co-injected with GATA4 and Dkk-1 showed evidence of cardiac differentiation (GFP activity) at stage 37. (G, G′) Cardiac expression is maintained in dorsal transplants at stage 40. Beating activity was never detected in dorsal transplants. (H, H′) Double WMISH shows overlapping expression between myl7 and myl3 (black arrowhead) and regions of myl7 expression alone (white arrowhead) in 35% of dorsal transplants (n = 84; the remaining transplants were negative for cardiac gene expression). a, atrium; ih, interhyoid muscle of the jaw; t, transplant; v, ventricle. The scale bar corresponds to 100 μm.