Fig. 1. The phenotype of tfap2a mutant embryos. (A) Live wild-type and (B) tfap2a mutant embryos at 4 dpf. Jaw defects, a slightly smaller head and reduced pigmentation in the tail characterize mob mutant embryos. (C-J) Detection of th expression in zebrafish embryos at 54 hpf by whole-mount in situ hybridization. (C,E) th expression is normal in the forebrain of tfap2a mutant embryos. (D,F,G,I) At 54 hpf, no th expression is detectable (white arrows) in the hindbrain of tfap2a mutant embryos. (H,J) th expression cannot be detected in tfap2a mutant embryos in the region where sympathetic ganglia form in wild-type. (K-P) Detection of dbh expression in zebrafish embryos at 4 dpf by whole-mount in situ hybridization. (K,M,N) At 4 dpf, dbh expression can be detected in the wild type in the locus coeruleus, the medulla oblongata/area postrema, sympathetic neurons as well as a group of arch associated neurons that may later contribute to the carotid body. (L,O,P) In tfap2a/mob^m819mutant embryos, the arch associated NA neurons develop normally, but cells of the locus coeruleus and sympathicus do not express dbh. A small number of cells starts to express dbh in the medulla oblongata/area postrema: both the number of cells and the expression level of dbh are severely reduced when compared with wild type. (Q-T) Immunohistochemistry with anti-serotonin antibodies reveals that the development of serotonergic neurons in the forebrain (Q,S) and hindbrain (R,T) is not affected in tfap2a mutant embryos. (A-T) anterior towards the left; (A-C,E,K,L) lateral views; (D,F-J,M-T) dorsal views. (A,C,D,G,H,K,M,N,Q,R) Wild-type; (B,E,F,I,J,L,O,P,S,T) tfap2a/mob^m819 mutant embryo. AAC, arch associated cluster (carotid body); DDC, ventral diencephalic dopaminergic cluster; LC, locus coeruleus; MC, medulla oblongata noradrenergic cluster; ObC, olfactory bulb dopaminergic cluster; s, somite; symp, sympathetic neurons.

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