Fig. 4

Myod^fh261 mutants lack head muscles and have defects in cartilage morphogenesis. In situ RNA hybridisation for miR-206 (A), myog (B), myhz1 (C,E) and klf2b (E) or immunodetection of MyHC (MF20, D; A4.1025, F). Ventral (A,D and left panels of B and C), lateral (F, right panels of B and C) or dorsal (E) views, anterior to left. A. Myod morphant and myod^fh261 mutant have similar loss of most cranial muscles except sternohyoideus (yellow arrows). B–D. In myod^fh261 mutants, myog and myhz1 mRNAs and MyHC are lost from many cranial muscles (blue arrows). Expression remains in sternohyoideus (yellow arrows). Weak myog mRNA is detected in adductor mandibulae (B, black arrows) and occasional fibres differentiate in adductor mandibulae. Hypaxial muscles (C, green arrows) seem unaffected and pectoral fin muscles (B–F, white arrows, dotted area in F) are variably reduced. E. In myod^fh261 mutants, most head muscles are consistently missing, even though sternohyoid (yellow arrows) and cartilage precursors expressing klf2b are present, Pectoral fin muscle is variably reduced (white arrows). F. Higher magnification shows that levator and adductor operculi are partially spared in myod^fh261 mutants, whereas pectoral fin and other muscles are missing, revealing the underlying somitic muscle (s). do, dilatator operculi; ah, adductor hyomandibulae; lo, levator operculi; ao, adductor operculi; l–5, levator 5; pp, protractor pectoralis. Bars = 100 μm.