Figure 4.

Second-order precursors for both the apical and the preapical bristle form on all three legs. The apical bristle precursors on T3 lose their neural markers but survive. (A–E) Leg imaginal discs of the neu-lacZ line 4–4.5 h APF stained with anti-β-galactosidase (green), with anti-Pox-neuro (red) and with anti-Cut (blue). Mechanosensory bristles appear blue-green. (A) First leg. The inset frames the distal tibia and is magnified in B. (B–E) Close-up of the distal tibia in the three legs. Second-order precursors for the preapical (arrowhead) and the apical bristle (double arrowhead) are found in all three legs. Preapical bristle precursors are in close proximity to the tibial chordotonal organ precursors (asterisk). (F–I) Leg discs from a white prepupa of the neu-lacZ line, 4.5 h APF stained with anti-β-galactosidase (green) and anti-Cut (red). Sensory organs are marked as above. Insets show Cut expression of the precursors. (F) Preapical and (G) apical bristle precursors of the second leg; (H) preapical and (I) apical bristle precursors of the third leg. Cut expression has faded from the apical bristle precursors in the third leg, while anti-β-galactosidase expression still marks the cells (I).