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Fig. 6. Gene expression in the intramandibular and primary jaw joint. Lateral views (A–C), dorsal views (I–M), and sections (E–G) are all shown with anterior to the left. Anterior views in (D and H). All black arrows mark the primary jaw joint, and all black arrowheads mark the intramandibular joint. (A–C) lateral views of whole-mount ISH for (A) nkx3-2-b, (B) nkx3-3, and (C) gdf5 at st. 41. Red lines depict the plane of section in the corresponding panel below each whole-mount photo, black arrows mark the future primary jaw joint, and the black arrowhead marks the future intramandibular joint. (D) Anterior view of whole-mount ISH for gdf5 at st. 45. (E–G) Sections of st. 41 larvae showing expressions in the future intramandibular and primary jaw joints. (E) nkx3-2-b is expressed in a broad domain surrounding the nascent primary jaw joint (black arrow), and also medially in the future infrarostral (white arrowhead) and future basihyal (white arrow). (F) nkx3-3 expression is found in the primary jaw joint (black arrow). (G) gdf5 expression is found in the nascent intramandibular joints (black arrowheads), and primary jaw joint (black arrow). (H) st. 45 whole-mount ISH for nkx3-2-a, shows expression in the primary jaw joint (black arrow). (I–L) dorsal views of st. 45 whole-mount ISH showing mandibular expression of (I) hand1, (J) barx1, (K) hand2-a+barx1 (double ISH; see Methods section), and (L) gdf5. Black arrowheads mark the future intramandibular joints. (M) Dorsal view with a ventral focal plane of a st. 48 X. laevis larva stained with alcian blue. Black arrowheads mark the intramandibular joints, black arrow marks the right primary jaw joint. (N and O) schematics of expressions showing hand2 (red), barx1 (green), and nkx3.2 (blue) in the mandibular arch. (N) wt and barx1 mutant zebrafish mandibular expression (adapted from Fig. 9B of Nichols et al., 2013). (O) st. 41 and st. 45 X. laevis mandible expression. The barx1 mutant zebrafish takes on a larval morphology strikingly similar to that of an anuran, with an extra joint forming within Meckel’s cartilage. Black arrowhead indicates the position of the future intramandibular joint. ir, infrarostral; mc, Meckel’s cartilage; pq, palatoquadrate. |
