Morphological and gene expression changes induced by TZ exposure. Whole body morphology is similar between embryos exposed to exogenous RA and to TZ starting at 24 hpf (A and B). Expression levels of a RARE reporter (C and D), hoxb5a (E and F), and cyp26a1 (G and H) are all increase after TZ treatment. Brightfield images (I and J) and expression of pitx2 (K–N) highlight the relatively posterior position of the mouth after TZ is applied. The black box in I, J, M, and N denotes the position of the developing mouth.

TZ exposure changes the position of the mouth and induces oral tooth formation in zebrafish. TZ treatment starting at 24 hpf results in a posteriorly positioned mouth by 78 hpf (surface staining A and B; shh^KI reporter C and D). Tooth germs are seen surrounding the mouth as visualized by the sp7 dental mesenchyme marker (GFP reporter E and F; mRNA ISH G and H) and dental epithelium marker dlx2b (mRNA ISH I and J; GFP reporter K and L). By 128 hpf, compared with a control lacking oral tooth germs (M), a TZ-exposed larva exhibits oral dental epithelial reporter expression as well as partial mineralization seen with alizarin red S staining (N and N’). By 150 hpf, compared with a control lacking oral tooth germs (O and P), a TZ-exposed larva exhibits oral dental epithelial reporter expression in a more anteriorly positioned mouth (Q and R). However, at this stage, we detect no evidence of partial mineralization. Boxed region in N is zoomed in for N’. Abbreviations: cb: ceratobranchial, m = mouth, mc = Meckel’s cartilage, mx = maxilla, op = opercle, ot = oral tooth germs/teeth, pt = pharyngeal tooth germs/teeth.