Fig. 3

Fig. 3 fa93e10 expression delimits cycles of cell proliferation. (A) A diagrammatic representation of a longitudinal section through a zebrafish caudal fin. Two hemirays are seen enclosing the intraray fin mesenchyme. The mesenchymal compartment is surrounded by a basement membrane and an epithelium, fa93e10 is expressed in the basal layer of the epidermis, illustrated in dark blue. For the purposes of counting proliferating cells (see F), the intraray mesenchyme was divided into a distal portion (distal most 250 µm, equivalent to one segment length) and a proximal portion (everything proximal to the distal portion). (B–E) Brightfield and fluorescence microscopy of longitudinal sections through a fa93e10-positive (B, C) and a fa93e10-negative (D, E) fin ray. (B) Brightfield illumination demonstrates fa93e10 expression in the basal layer of the epithelium (black arrowheads). (C) Fluorescence illumination of the same section (B) demonstrates 6 BrdU-labeled cells in the distal intraray fin mesenchyme (white arrowheads). Six epithelial cells are also highlighted (white arrows). (D) A representative fa93e10-negative section. (E) Fluorescence illumination of the same section (D) illustrates 3 BrdU-labeled cells in the epithelium (white arrows) but none in the mesenchyme. (F) Fifty contiguous longitudinal sections were cut from 6-month-old fa93e10-positive (n = 4) and fa93e10-negative (n = 5) fins that had been in vivo labeled with BrdU. Following BrdU immunohistochemistry, labeled cells in the distal intraray mesenchyme were counted. Labeled cells in the proximal intraray mesenchyme and epithelium were excluded. Values represent the mean number of BrdU labeled cells per 50 sections ± SD.