Fig. 2. Regulation of hb within the NB7-3 lineage. Embryos double labelled for the NB7-3 lineage marker Eg (magenta) and Hb (green). Midline is towards the left. Insets show Eg expression separately. (A-C) Hb expression during normal NB7-3 lineage development. At late stage 11 the NB has divided once to generate the Hb⁺ GMC7-3a (A). After hb downregulation the NB has divided again, and Hb is only detectable in GMC7-3a (B). At stage 14 the progeny of GMC7-3a (GW and EW1) express Hb, whereas the progeny of GMC7-3b (EW2) and GMC7-3c (EW3) are Hb^- (C). (D-F) Hb expression in svp^e22. Even after the generation of the second GMC, the NB has not yet downregulated Hb (E). At stage 14, three instead of two Hb⁺ neurons can be detected in many cases (F). Note that not all NB7-3-derived cells express Hb. (G-I) Hb expression in pros^C7. In pros^C7, the NB generates a Hb⁺ GMCa as normal (G) but the expression is not maintained (H,I). (J-L) Hb expression in svp^e22, pros^C7. After the first division Hb has not been downregulated in the NB (K), which results in a svp-like phenotype at stage 14 (L). (M) Scheme of normal NB7-3 lineage development, with markers used in our analysis. (N) Continuous expression of Pros within the NB inhibits the downregulation of Hb. All cells of the NB7-3 cluster are Hb⁺. (O) pros^C7/Df(3L)H99 double mutant. There are no NB7-3-derived Hb⁺ cells present in the absence of apoptosis. Scale bar: 20 µm.