Figure 2. Hb does not directly activate hb transcription, but is required within the neuroblast for subsequent expression of HA:Hb in neuronal progeny born during the competence window.
(A) Prolonged Hb expression in NB7-1 results in all Eve+ neurons being Hb+, but only ~5 Eve+ neurons are HA:Hb+. Stage 14 embryo (en-gal4 UAS-hb HA:hb).
(B) Only ~5 Eve+ neurons are HA:Hb+ (blue) in 2nd instar larvae (en-gal4 UAS-hb HA:hb).
(C) Ectopic Hb protein in post-mitotic neurons (green) does not induce HA:Hb expression (blue). Only early-born U1/U2 neurons express HA:Hb. Ventral view, stage 16 (eve-gal4 UAS-hb HA:hb).
(D) Ectopic Hb protein in neuroblasts (green; NBs, arrows) does not induce expression of HA:Hb expression (blue) within neuroblasts. Lateral view, stage 11 (insc-gal4 UAS-hb HA:hb). Also see Figure S1.
(E) Schematic summary. Blue indicates endogenous HA:Hb, whereas green indicates Hb protein generated from UAS-hb ectopic overexpression. Blue bar at the bottom indicates active hb transcription in the neuroblast; white bar indicates the NB7-1 early competence window, when ectopic Hb in the neuroblast can induce HA:Hb expression in neuronal progeny.