Fig. 1. Development of the GF system. (A) GF development. The timing of events is based on the work presented in the present paper as well as the dye injection work of Jacobs et al. (Jacobs et al., 2000). The time line is recorded as percent of pupal development with time zero according to Bainbridge and Bounds (Bainbridge and Bounds, 1981). The phases indicated below the time line were determined experimentally in the present work. The time of dye coupling was determined by Jacobs et al. (Jacobs et al., 2000). t1, t2 and t3: first, second and third thoracic neuromere. (B) Expression patterns of the three Gal4 constructs. (B1) Simultaneous staining of the GF (with c17) and the TTMn (with shakB-Gal4) at 33% of pupal development. In this particular specimen, the left GF has reached the TTMn and the right GF has not. (B2) When driven by shakB-Gal4, lacZ is expressed in the postsynaptic motoneurons and TTMn exhibits the strongest staining. (B3) The P[Gal4]a307 enhancer is expressed strongly in the GF and more weakly in the postsynaptic cells. In this specimen both GFs are labeled and the dendrites of the left TTMn are revealed. (B4) The P[Gal4]-c17 enhancer is expressed in the GF but not in the motoneurons. The developmental stage of each specimen is indicated in the lower right of each panel. Scale bar: 20 µm.