Fig. 3

stm^hy024 mutants show myogenic defects specifically in opercular muscles. (A-H) In situ hybridisation with tbx1 (A,B) and capsulin (C,D) probes reveals that muscle specification is unaffected in the pharyngeal arch muscle precursors of stm^hy024. However, both myf5 (E,F) and myod (G,H) expression are reduced in stm^hy024 relative to wild type (WT). Arrowheads indicate muscle primordia. (I-L) Fluorescent in situ reveals that myod expression is reduced specifically in the precursors of the lo and ao at 52 hours post-fertilisation (hpf; I,J) but is unaffected in the adjacent ah. At later stages, there are fewer En2-expressing (En2⁺) muscle cells specifically in the do but not the lap of stm^hy024 (K,L). Brackets indicate do muscle cell nuclei. (M) Quantification of En2⁺ muscle precursors in stm^hy024 (blue) and WT (red) at 48, 52 and 56 hpf reveals that stm^hy024 mutants have fewer muscle precursor cells than WT in the lap or do primordia from 56 hpf (mean ± s.e.m.). Pharyngeal arches 1-7 are shown by numbering in A-F. ah, adductor hyoideous; ao, adductor operculi; do, dilator operculi; e, eye; lap, levator arcus palatini; lo, levator operculi. Scale bars: 50 μm in A-H,K-L; 20 μm in I,J.