Fig. 5

Inner ear and pharyngeal arch defects in val- larvae. (A,B) Horizontal sections of 5-day wild-type (A) and val^b337 (B) larvae showing complete fusion of the developing semi-circular canals in the mutant. Anterior is to the top. This phenotype was observed with varying severity in 21/22 val^b337 larvae examined, and 13 of these 22 mutant larvae circled in response to a gentle touch to the side of the head rather than swimming away in a straight line (1/50 wild-type larvae exhibited this behaviour). a and p indicate anterior and posterior semi-circular canals, respectively. (C-G) Alcian-blue stained pharyngeal arch-derived cartilages of 7- day wild-type (C, D) and val^b337 (E-G) larvae. (C) The ventral cartilages of pharyngeal arches 2-7 in ventral view with anterior to the top. The second (hyoid) arch elements include paired ceratohyals (ch) and interhyals (ih). Medially, ch overlies the unpaired median basihyal (bh). The third through seventh (gill-bearing) arches each include paired ceratobranchials (cb1-5) and hypobranchials (hb1 labelled) which are adjacent to the unpaired median basibranchial (bb). (D) The third arch-derived cartilages of a wild-type embryo, dissected away from the surrounding tissue. Abbreviations are as for C. Note that cb1 is a tapering element, one cell wide through most of its length, and that it is separated from the median bb by hb1. (E-G) Third arch-derived cartilage elements of three val^b337 larvae, with abnormalities including variable thickening and truncation (E,F); ectopic interhyal-like elements that are partially fused to (F; arrowhead) or separate from (G; arrowhead) cb1; and medial extensions of cb1 such that cb1 overlies bb (F; arrow). Scale bars in A-C = 100 μm D-G = 50 μm.