Pharyngeal endoderm and cranial NCC defects in animals lacking Fgf8 and Fgf3. nkx2.7 (A-D) and axial (E-H) label pharyngeal endoderm during early pouch morphogenesis stages (18 hpf). nkx2.7 and axial are in blue, and, in E-H, krox-20 in red labels R3 and R5. In wildtype animals (A,E), the first pouch (p1: arrows) has formed anterior to R3, and a more posterior endodermal mass that will give rise to the remaining pouches (black lines) is situated adjacent to R4-R6 territory. The first pouch is variably lost in fgf8– animals (asterisk in B, question mark in F). Whereas pharyngeal endoderm develops normally in fgf3-MO animals (C,G), in fgf8–; fgf3-MO animals (D,H) pharyngeal endoderm is present as a single anterior mass (black line) and no pouches are evident. (I-P) dlx2, in blue, labels cranial NCC; in red (I-L), pax2a labels the MHB and krox-20 labels R3 and R5. (I) In 18 hpf wild-type animals, mandibular (1), hyoid (2), and branchial (3) NCC streams give rise to seven pharyngeal arches. (M) At 33 hpf, the third branchial stream has generated arches 3-5 and arches 6 and 7 have yet to separate. In fgf8– (J,N) and fgf3-MO (K,O) animals, the migration and coalescence of NCC to form the pharyngeal arches is largely normal. In fgf8–; fgf3-MO animals, the mandibular (1) stream is disorganized and hyoid and branchial streams are fused together (2/3) at 18 hpf (L). By 33 hpf (P), nearly all hyoid and branchial NCC are absent, and mandibular (1) NCC are present but reduced. Anterior is to the left in all panels. A-D are dorsal views, and E-P are lateral views. R3 and R5, rhombomeres 3 and 5; MHB, midbrain-hindbrain boundary; p1, first pouch. Scale bar: 50 µm.
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