hand2 is required for ventral pharyngeal cartilage and the jaw joint but not for the second arch joint. (A,B) Lateral views of wholemount 4-day old wild type (A) and hand2 mutant (B) larvae stained with Alcian Green, revealing severe loss of ventral pharyngeal cartilage in the mutant. (C-I) Flat-mounted pharyngeal cartilages from wild type (C,F) and hand2 mutants (D,E,G-I). (C-E) Flat-mounted pharyngeal cartilages from the first six arches in wild type (C), and the entire pharynx in two different hand2 mutants (D,E). In hand2 mutants, ventral cartilages (arrowheads) are severely reduced. The two upper jaws are connected by a continuous cartilaginous bridge (asterisk), although some hints of partial jaw joint formation are evident (see Table 2). Branchial cartilages are also absent in hand2 mutants. The upper hyomandibular region of the hyosymplectic in E was slightly nicked during dissection and resembled the contralateral counterpart. (F-I) Flat-mounted pharyngeal cartilages from one side of the first and second arches. The prominent ventral cartilages (M, ch) present in wild type (F) are absent in hand2 mutants, although a small jumbled mass of ventral second arch cartilage is invariably present (arrowheads, see Table 2). (G-I). The dorsal cartilages are relatively well patterned with distinctive PTP and SY elements visible. The second arch joint (arrows) is present in hand2 mutants. Because of the highly penetrant jaw joint loss (see Table 2), the hand2 mutants in G-I were cut during dissection in order to flat-mount; the line indicates the plane of cutting and where the upper jaw was fused to its contralateral counterpart (asterisk in D,E). bh, basihyal; cb1-4, ceratobranchial 1-4; ch, ceratohyal; hm, hyomandibula; hs, hyosymplectic; ih, interhyal; M, Meckel′s; pq, palatoquadrate; ptp, pterygoid process of palatoquadrate; sy, symplectic. Scale bars: 100 μm in A-E, 50 μm in F-I.
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