Figure 1.

Development of the posterior sternopleural bristle in the third leg ceases after proneural cluster initiation—no precursor segregation takes place. (A) Summary table. Sternopleural proneural clusters were identified as cells staining for GFP expressed with the sca-Gal4 line. (B–E) Leg imaginal discs of two individuals from the time interval 25–16 h BPF during which the cluster (triangle) emerges in T2 and T3 and also disappears in T3. One individual shows a few GFP positive cells in the dorsal outer ring in the second (B) and the third leg (C). The other individual shows several GFP positive cells in the dorsal outer ring only in the second leg (D), not in the third leg (E). (F,G) Sensory organ precursors at the white prepupa stage. A sternopleural bristle precursor is found in the second leg (triangle) but not the third leg. Discs of the neuralized-lacZ line were stained with anti-β-galactosidase (green) and with anti-Pox-neuro (red). In the second leg disc (F), the sternopleural bristle precursor (triangle) is located in the outer ring of the disc dorsal to the large femoral chordotonal organ (asterisk).