Reducing Nr2f Gene Dosage Can Fully Rescue the Lower Jaw in edn1 Mutants
(A–E) Facial skeletons of fish carrying nr2f and/or edn1 mutations, schematized in (A′–E′). Compared to the control (A), nr2f2; nr2f5 mutants (B) have a thickened upper jaw (double arrowhead), while edn1 mutants (C) have a much reduced lower jaw. Reducing Nr2f alleles in edn1 mutants (D and E) can rescue the jaw joint (black arrows) and Meckel's cartilage (compare C with D–E). The upper jaw is still enlarged in nr2f2; nr2f5; edn1 combinatorial mutants (E, double arrowhead). M, Meckel's cartilage; Ptp, pterygoid process; jj, jaw joint. Scale bar in (E) 50 μm.
(F and G) Quantification of jaw joint (F) and Meckel's rescue (G) across different summed nr2f; edn1 genotypes. One or both jaw joints were rescued in 12/106 mutants lacking three to six Nr2f alleles. See Figure S6 for Meckel's scoring system. n = 16, 29, 30, 53, 42, 10, and 2 for edn1 mutants with zero to six mutant Nr2f alleles, respectively. Error bars are the SEM. Scores in (G) were non-evenly distributed across genotype classes (p < 0.0001, chi-squared).
(H–J) dlx5a (H), dlx6a (I), and hand2 (J) (magenta) are expanded in nr2f2; nr2f5 mutants (white arrowheads), reduced in edn1 mutants, and restored in the first arch of nr2f5; edn1 mutants (nr2f1b/nr2f2 genotypes indicated). Some ectopic expansion into maxillary cells was still evident in the combinatorial mutants (white arrowheads), yet second-arch expression was not restored (double arrowheads). dlx2a (green) labels arch NCCs, and dashed lines in (J) indicate arch boundaries.
(K) Ectopic ventral expression of jag1b (magenta) and prrx1b (green) in edn1 mutants (white arrows) is reversed in the mandibular (asterisk) but not hyoid (double arrowheads) domains of nr2f1b; nr2f2; nr2f5; edn1 mutants. White outlines depict the first endodermal pouch.
Scale bars in (E) 50 μm, (H–K) 20 μm.