We have used the green fluorescent protein (GFP) from the jellyfish Aequorea victoria as a vital marker/reporter in Drosophila melanogaster. Transgenic flies were generated in which GFP was expressed under the transcriptional control of the yeast upstream activating sequence that is recognized by GAL4. These flies were crossed to several GAL4 enhancer trap lines, and expression of GFP was monitored in a variety of tissues during development using confocal microscopy. Here, we show that GFP could be detected in freshly dissected ovaries, imaginal discs, and the larval nervous system without prior fixation or the addition of substrates or antibodies. We also show that expression of GFP could be monitored in intact living embryos and larvae and in cultured egg chambers, allowing us to visualize dynamic changes in gene expression during real time.

To identify genes that are expressed in specific cell types or tissues during development, we generated enhancer-trap lines in which the yeast transcriptional activator, GAL4, was mobilized throughout the Drosophila genome. The GAL4 lines are part of a two-part system involving GAL4 and its target, the upstream activating sequence (UAS). Detection of GAL4 expression patterns was achieved by crossing individual GAL4 lines with flies carrying the reporter gene lacZ under the transcriptional control of the UAS followed by histochemical and immunocytochemical staining. Here, we present the results of this screen and the characterization of GAL4 lines that show distinct patterns of gene expression during Drosophila development, including embryogenesis, oogenesis, and imaginal disc development. However, we were unable to identify GAL4 lines that were expressed within the germ line or during early embryogenesis. Furthermore, consistent with previous results, we found that the GAL4 enhancer trap technique had a much lower frequency of transposition than has been reported for lacZ enhancer trap screens. Taken together, these results demonstrate both the strengths and weaknesses of the GAL4 enhancer trap technique for identifying unique patterns of gene expression during development.

No abstract