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Fig. 5 Elimination of han expression sites in the pharyngeal area does not influence thyroid development. Labelling is as in Fig. 1. (A-D) In edn1 morphants (B), han (hand2) expression in the first (1) and third branchial arches is eliminated. In tfap2a(low, lockjaw) morphants (C), hand2 expression in the second branchial arch (2) is missing. In double morphants (D), hand2-expressing cells are only present in arch-associated cells (arrowheads), as well as some weak expression in the endoderm (confirmed on sections, data not shown). (E) The thyroid (arrow) appears normal in edn1/tfap2a double morphants. (F) In foxi1 morphants, hand2 expression in arch-associated cells (arrowhead) is specifically ablated. (G) Normal expression of nk2.1a in foxi1 morphants (arrow). h, heart.