Continual and direct requirement for Hedgehog signaling in caudal fin development. A-D, Schematic representation of the time span of the experiment (black stripe), cyclopamine treatment (red stripe) and time of analysis of embryos (green arrow) are shown on the left. Tail of zebrafish embryos at the time of analysis are shown on the right. Bright field (top panels in A) and fluorescence signals (lower panel in A and B-D) of representative samples of zebrafish embryos are shown. A, No GFP expression in the fin fold mesenchyme in cyclopamine treated embryos (cyclop, arrow) in comparison to control ethanol treated embryos (EtOH, arrow). B-D: Cyclopamine treatment from 24 to 48 h results in reduction of GFP expression. E-M: Cell autonomous and non-autonomous requirement for smu in development of caudal fin primordium. E-G: transplantation of wild type transgenic cells targeted in the ACFP results in donor cells in the fin fold mesenchyme (arrows in F) with activated GFP (arrows in E, G). H-J: Transplantation of smu-/- transgenic cells into wild type embryos results in rhodamine labeled cells in the fin fold mesenchyme (arrow in I) but these cells do not express GFP (arrows in H, J). K: smu-/- transgenic cells in the floor plate activate gfp expression (arrow). L, M: Transplantation of wt transgenic cells into smu-/- non-transgenic embryos results in rhodamine labeled cells excluded from the fin fold mesenchyme (arrows). Tail region of 72 hpf embryos are shown anterior to the left. Abbreviation: n, notochord.