Figure 1 legend:

The GAL4-UAS binary system of Drosophila melanogatser (Brand and Perrimon, 1991) allows cell lineages to be identified by expression of green fluorescent protein (GFP). With this system, cell-specific expression of the yeast GAL4 protein induces transcription of GFP when it binds to GAL4 binding sites (UAS, Upstream Activation Sequence) in the promoter region of the GFP gene. We have used the 201 Y-GAL4 line to label a subset of mushroom body neurons in culture (Yang et al., 1995) by expressing either GFP or n-syb-GFP (a fusion construct containing the neurons form of synaptobrevin and GFP, Estes et al., 1999).

Green Fluorescent protein (GFP) expression does not interfere with the fura-2 signal evoked by high K+ depolarization. (A) A phase-contrast image of a GFP expressing giant neuron is shown including the zone (red square) where [Ca2+] was quantified. (B) Psuedocolor images of basal and peak Ca2+ were taken on the GFP and fura-2 channels upon high K+ depolarization (see color scale bar in C for Ca2+ levels). Ca2+ measurements from each channel are quantified in (C). Black bar in C indicates the duration of stimulation by 60 mM K+ -containing saline.