Fig. 7

Scxa;scxb double mutants have a jaw phenotype and severe musculoskeletal defects. A–C′) Live transmitted light and red fluorescent images in lateral view, anterior to left of genotyped scxa^−/−;scxb^−/− double mutants (A′–C′) compared with siblings (A–C, shown is scxa^+/−scxb^+/−). Mutants show a hanging open jaw. The col2a1:mCherrytransgene (B) shows the dropping Meckel’s cartilage (mc). At 13 dpf, fish are much smaller than siblings (whole-fish insets in C). D) Confocal stacks of immunodetection of MyHC (A4.1025) and Tsp4b in 4 dpf embryos of scxa^−/− scxb^−/− showing normal distribution of Tsp4b and normal muscle structure (compare with Fig. 6C). E–G′) AB/AR staining for cartilage and bone for scxa^−/−scxb^−/− (E′–G′) and sibling from the same cross (E–G) shown in lateral (E) and ventral (F, G) views that show the hanging jaw phenotype. The magnified area from mc shows many less differentiated rounded cells at its most anterior tip, near the joint (arrow, G′) compared with elongated mature cells in sibling (arrow, G). H–I′) Confocal stacks showing immunodetection of cranial muscles (MyHC, A4.1025) and tendons (Tsp4b) of 4 dpf embryos of scxa^+/−; scxb^+/− incross in ventral view. Tsp4b is highly reduced in tendons and ligaments of double mutants as shown for mandibulohyoid junction (mhj) (magnified area, II′). Many muscle fibers in scxa^−/−; scxb^−/− extend the length of the intermandibularis posterior (imp) and the interhyoideus (ih) (yellow arrowheads, I′), whereas others extend far beyond their normal end at the mhj until their meeting point (white arrowheads, I′). All scale bars, 100 µm. Hhj, hyohyoideus junction; ih, interhyoides; ima, intermandibularis anterior; imt, intermandibularis tendon; mat, Meckel’s adductor tendon; mc, Meckel’s cartilage; pq, palatoquadrate cartilage; sh, sternohyoideus; sht, sternohyoideus tendon.