Pharyngeal arch primordia are mispatterned in response to changes in Zic2a levels. (A–H) Embryos stained by ISH for dlx2a. (A) Four streams of NC cells that populate the pharyngeal arches express dlx2a (42/44, 3 exp.). (B) The dlx2a domain is reduced in PA1 and 2 of zic2a morphants (13/30, 3 exp.). (C) Zic2b knockdown has no effect on dlx2a expression in the PAs (40/44, 3 exp.). (D) The first two pharyngeal arches are reduced in some double morphants (15/46, 3 exp.), while other embryos have a reduction of dlx2a in PA3 and PA4 (11/46, 3 exp., shown in D) or all four PAs (10/46, 3 exp.). (E,F) After HS induction at 10 hpf, some Zic2aYFP-positive embryos are wild-type (13/64 embryos, 3 exp.), some have an elongated PA1 (21/64, see arrow in F) and some have reduced dlx2a staining in the arches (28/64). (G,H) Dlx2a expression remains unchanged after Zic2aYFP induction at 14 hpf (15/17, 1 exp.). (I–L) Transplant host embryos stained for biotin and alcian blue at 4 dpf. (I,J) Transplanted control morphant cells incorporated in the pterygoid process, palatoquadrate, and ethmoid plate of control morphant embryos (see arrowheads). (K,L) Transplanted Zic2a-deficient cells incorporated into the hyoid arch and the ethmoid plate of control morphant embryos. (L) Some control morphant host embryos develop with abnormal trabecular cartilages (see asterisks). (A–H) are dorsal views with anterior to the left. I–L are dissected pharyngeal and neurocranial cartilages. (I′,J′,K′ and L′) are close-up views of (I–L). Abbreviations: ep—ethmoid plate, h—hyoid, m—mandibular, pp—pterygoid process, pq—palatoquadrate.
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