A comparison of zebrafish and stickleback pharyngeal tooth replacement. a, b Zebrafish and stickleback first tooth replacement events, respectively. Alizarin stained and dissected ceratobranchial 5 elements and their teeth from both species at 4 dpf zebrafish (a) and 30 dpf stickleback (b). Anterior to top. Arrows indicate first replacement tooth germs (bilaterally paired). Note that the zebrafish germs form on the ventral/medial side of the predecessor pioneer tooth (which in this case is the middle of 3 the ankylosed teeth on each side, tooth 4v1). Inset box in b magnified in b’ shows first replacement tooth. c, d Replacement histology on the coronal (d) and oblique coronal (c) axes (see Methods). Arrowheads mark the putative successional dental epithelium (SDE) in each image. In zebrafish, this tissue takes the form of a true successional dental lamina (SDL). In sticklebacks, there is only a subtle, non-elongated epithelial thickening that surrounds the tooth shaft like a collar, immediately beneath the rest of the nearby epithelial tissues (see Additional file 1: Fig. S1 for sagittal view). Arrows mark tooth germs at the stages indicated. A bracket marks the tight epithelial association between an early tooth germ and the position of the presumed SDE. Scale bars in a and b = 100 μm; c and d = 20 μm
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