Figure 3.

Reduced mesenchymal and expanded epithelial expression of freshwater enhancer relative to marine enhancer in developing ventral pharyngeal teeth. Ventral pharyngeal tooth plates from fish doubly transgenic for two alleles of the Bmp6 intron 4 enhancer driving two different reporter genes (A, D): the marine enhancer driving mCh with the freshwater enhancer driving eGFP (B, C) and the marine enhancer driving eGFP with the freshwater enhancing driving mCh (E, F). Bilateral ventral pharyngeal tooth plates (B, E) are shown, next to representative teeth from three stages (C, F): early (early bell), middle (late bell), and late (functional) highlighted by white boxes in B, E. (C, F) Early: freshwater and marine enhancer drove expression in the epithelium (black arrowheads), with concentrated expression in the tip (asterisk), and more overall epithelial expression from the freshwater enhancer. Both enhancers also drove expression in the mesenchyme (solid white arrowhead) with a larger expression domain of the marine allele (yellow dotted line) compared to the freshwater allele (orange dotted line) seen in both genotypes. Middle: freshwater allele still drove expression in the epithelium while marine allele had reduced or undetectable expression outside concentrated tip. The marine allele drove more robust mesenchymal expression compared to the freshwater allele. Late: marine allele drove robust expression in the mesenchyme compared to freshwater allele in mineralized tooth (dashed line). Diagram: summary of tooth epithelial and mesenchymal domains. The relative sizes of green and magenta hatched lines correspond to the approximate relative strength of expression in the epithelium. Overlapping mesenchyme domain is gray, and expanded marine mesenchyme is marked with white arrowhead. Scale bars=100 µm (B, E), 50 µm (C, F). n=3 fish per genotype (6 total fish), >25 teeth per fish (304 total teeth).