Fig. 4. Comparison of serotonergic cells in segment A8 from wild-type and numb¹ mutant embryos. (A,D) Ddc immunoreactivity of stage 17 embryos showing the entire ventral cord and demonstrating that A8 cells are not absent in numb¹ embryos. T1-T3 are thoracic segments. A1-A8 are abdominal segments. E is the embryonic posterior Ddc cluster that is only visible during embryogenesis. (B,E) A magnification of A8 from the same CNS as in A,D, showing immunoreactivity of Ddc (red), Zfh-2 (green) and Hb (blue). The single Ddc-expressing cell in A8 shows Zfh-2 expression in wild-type and Hb expression in numb¹ embryos. (C,F) Stage 15 embryos immunostained with Eg (red), Zfh-2 (green) and Hb (blue). (C) A wild-type A8 hemisegment shows three Eg cells, two are Hb positive and one is Zfh-2 positive. (D) A numb¹ A8 hemisegment shows that Eg and Hb expression are unaltered, but Zfh-2 expression is reduced. Scale bars: in D, 15µm for A,D; in E, 10 µm for B,E; in F, 5 µm for C,F.