The enamel knot appears de novo at the tip of the incisor bud. Live imaging was used to study the spatiotemporal dynamics of the early and late signaling centers using Tcf/Lef:H2B-GFP and Fucci G1 reporters. (A) The explant was live imaged from E13.0 + 14 h. In still images of the time lapse with 3D surface rendering, GFP (bright green) was initially seen in the labial part of the growing bud in the same area with the G1 early signaling center (red). At E13.0 + 6 h, new GFP-positive cells appeared at the tip of the bud (light yellow), and consecutively G1 cells appeared (magenta) in the area forming the EK. The G1 early signaling center is marked with an arrowhead and the EK with an asterisk. Bar, 50 µm. (B) Quantification of representative live imaging samples. GFP-positive and G1 cells showed initially the same number, but there was a higher increase in the number of GFP-positive cells (nbuds = 3; data shown are means ± SD).
