Fig. 1

Stickleback pharyngeal tooth morphogenesis. All images show sagittal or transverse sections from sticklebacks (20–40 mm standard length). The basalmost layer of epithelium is outlined with yellow dashed lines in all panels, the mesenchyme is outlined in red. During late bell stages (e, k), the epithelium towards the apex of the forming tooth becomes thickened, no longer presents a clear bilayer, and will eventually be punctured during tooth eruption (gray outlines). a–f Staging series of hematoxylin and eosin-stained transverse sections through stickleback pharyngeal tooth germs at the stages indicated. Epithelium (“epi”) and mesenchyme (“mes”) are labeled in a. g–l Staging series of DAPI-stained sagittal sections through stickleback pharyngeal tooth germs at the stages indicated. Gray portions of dotted epithelium lines in J indicate the epithelium/tooth connection that was present on an adjacent section. Bone matrix is false-colored red in k and l. Scale bars = 20 μm