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Fig. 3 sspo mutants show loss of urp gene expression from CSF-cNs. (A) A wild-type embryo, showing urp1 expression in CSF-cNs (arrows). (B) An sspo-mutant embryo, showing reduction in levels of urp1 expression from CSF-cNs (arrows). (C) A wild-type embryo, showing urp2 expression in CSF-cNs (arrows). (D) An sspo-mutant embryo, showing almost complete lack of urp2 expression from CSF-cNs (arrows). Embryos shown in A–D are representative of a minimum of 25 embryos analysed for each genotype for each urp gene. (E) A wild-type embryo, showing urp1 expression in CSF-cNs after exposure to epinephrine (arrows). (F) An sspo-mutant embryo, showing urp1 expression in CSF-cNs after exposure to epinephrine (arrows). Note that expression level is indistinguishable from wild type. Embryos from mating of sspo-heterozygous fish were exposed to epinephrine in two independent experiments (25 embryos each). Since all embryos showed similar levels of urp1 expression, 13 embryos were randomly genotyped after in situ hybridisation from the second experiment, of which three were mutants. (G) A wild-type embryo, showing urp2 expression in CSF-cNs after exposure to epinephrine (arrows). (H) An sspo-mutant embryo, showing restoration of urp2 expression in CSF-cNs after exposure to epinephrine (arrows). Embryos from mating of sspo-heterozygous fish were exposed to epinephrine in two independent experiments (25 embryos each). 16 embryos from the second experiment, with urp2 expression in the spinal cord, were genotyped after in situ hybridisation, of which five were mutants. All embryos depicted in A–H were at 26 hpf. Scale bars: 100 μm.