Fig. 4

Expression of GFP in the regenerating caudal fin of BRE1189 and BRE510 zebrafish suggested that the blastema, osteoblasts of bony rays, and blood vessels were Bmp-responsive. There was no detectable expression of GFP in the regenerating BRE1189 fin blastema at 1dpa (A,A′), although strong GFP expression was observed in some amputated bony rays. GFP expression in scattered cells that were in line with amputated bony rays expanded in the regenerating fin from 2dpa (B,B′) to 3dpa (C,C′). By 4dpa (D,D′), two domains of GFP expression in regenerating BRE1189 fins became evident: a distal domain of scattered cells and a proximal domain of aggregated cells. (E-G′) From 6dpa to 10dpa, these two GFP expression domains were retained, with the proximal domain growing in size and being continuous with the amputated bony ray. By 20dpa (H,H′), GFP expression was greatly reduced in the regenerating BRE1189 fin. In the regenerating BRE510 caudal fin, very few GFP positive cells were observed at 1dpa (I,I′) and 3dpa (J,J′), but strong GFP expression was present in branching patterns along the amputated bony ray. By 4dpa (K,K′), GFP expression was seen in scattered cells at the proximal side of the fin regenerate along the same trajectory as the amputated bony rays. From 6dpa (L,L′) to 8dpa (M,M′) to 10dpa (N,N′), the distal domain of scattered GFP-positive cells extended gradually towards the distal tip of the BRE510 fin regenerate, and the proximal domain assumed a branching morphology that was continuous with the amputated bony rays. Panels A′-N′ are higher-magnification views of regions identified by the yellow boxes in panels A–N, respectively, and the dashed white line represents the site of amputation. n = 3 for each genetic group at each timepoint. Scale bars: A-N = 250 μm. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)