Fig. 1

Early development of the pharyngeal arches in chicken. a HH16 TFAP2α (brown staining) present in NCC, the negative core of pharyngeal arches is indicated (arrows). b, c HH22, Isl1 positive core of the pharyngeal arch (bold arrow); the NCC area of the arch and the arterial wall are negative (thin arrows). d–f HH27 from distal (d) to proximal (f), WT1 in the coelomic lining (arrowhead) and the mesenchyme are positive (arrowheads). Note NCC-derived arterial walls and condensed mesenchyme (* in f) are WT1 negative. Numbers 3, 4 and 6 indicate the various PAAs