Differential phenotypes observed in fin differentiation for tbx5a mutants versus tbx5b morphants. A-J: Embryos at (A-C) 36 hpf; (D-F) 42 hpf; (G-I) 46 hpf; (J) 36 hpf. A: hand2 is expressed in mesenchyme of the wild-type fin bud. B: In tbx5a mutants, no pectoral fins develop; hand2 expression was absent in presumptive fin buds (brackets indicate region of expected expression) although present in pharyngeal arches. C: In tbx5b morphants, fin buds expressed hand2 in the mesenchyme in proportion to fin size. D: vcana expression in apical fold (AF) and otic placode (o). E: vcana expression missing in region of expected fin buds. F: vcana expression missing or barely detectable (*) in fin buds. G: bmp4 expression in eye, otic placode and AF of pectoral fin. H: No bmp4 expression in fin bud region. I: bmp4 expression can occur in AF (arrow); and was robustly detected in the mesenchyme of the fin bud. J: In younger embryos bmp4 was similarly detectable in mesenchyme and AF as it begins to form. AF, apical fold; e, eye; o, otic placode; p, pharyngeal arches; arrowhead, fin bud mesenchyme; arrow, AF; * barely detectable AF/mesenchyme expression; brackets, region of expected fin bud formation.
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