Fig. 4

FGF signaling stepwise regulates the formation of the mesoderm-derived structures. (A1-A5) Panels show the morphology of wild type embryos at the time points indicated by the solid yellow circles. Treatments were performed at the same time points, and embryos were observed at the time points indicated by the blue circles. (B1-B6) Phenotypes of the tornaria larvae treated with DMSO (B1) or PD173074. PD173074 was applied at different stages of development, indicated by the yellow circles on the left (B2-B6). (C1-D4) The tornaria larvae (73 hpf) treated with PD173074 (C2-C6) or bFGF (D2-D4) at different developmental stages were stained with Phalloidin (green). The penetrance of the drug effects was high (> 99%) when treated at either 18 or 40 hpf. When treated at 23, 26 or 31 hpf, ~ 70% of the larvae did not exhibit a muscle string. The efficiency of bFGF protein was consistently high (> 99%) for all the treatments. The larvae were counterstained with Hoechst 33,342 for nuclei (blue). e Illustration of a tornaria larva with mesodermal structures in red. The pharyngeal muscle, the muscle string and the hydroporic canal are indicated. The scale bar in A1 is shown for panels A1-B6, and the scale bar in C1 is shown for panels C1-D4. Abbreviations: ms, muscle string; pm, pharyngeal muscle; hc, hydroporic canal