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Fig. 5 Fgf and RA signaling regulate prdm1a expression in the pharyngeal arches. A,B: Embryos treated with DMSO, as a vehicle control, showing prdm1a expression at 35 hpf. C,D: Treatment with 20 μM SU5402 from 29-35 hpf shows reduced expression of prdm1a in the arches, otic vesicle (arrow), and fin bud. Expression remained in the hatching gland and cloaca (not shown). E,F: Treatment with 50 μM DEAB from 29-35-hpf shows reduced prdm1a expression in the posterior arches (par) and mildly in the fin bud (fb). G,H: Treatment with 0.1 μM RA from 29-35-hpf dramatically increased prdm1a expression in the arches and slightly in the fin bud. prdm1a expansion appears to be endoderm/arch-specific as staining does not cross into the dorsal midline/medial endoderm. All embryos were fixed after treatment and in situ hybridization performed at 35 hpf. A,C,E,G: Lateral views; dorsal to the top, anterior to the left. B,D,F,H: Dorsal views, anterior to the left. e, eye; fb, fin bud; ov, otic vesicle; par, pharyngeal arch region. Bracket in G indicates extent of prdm1a expansion.