DISTINCT EXPRESSION PATTERNS DETECTED WITHIN INDIVIDUAL TISSUES BY THE GAL4 ENHANCER TRAP TECHNIQUE

To identify genes that are expressed in specific cell types or tissues during development, we generated enhancer-trap lines in which the yea st transcriptional activator, GAL4, was mobilized throughout the Droso phila genome. The GAL4 lines are part of a two-part system involving G AL4 and its target, the upstream activating sequence (UAS). Detection of GAL4 expression patterns was achieved by crossing individual GAL4 l ines with flies carrying the reporter gene lacZ under the transcriptio nal control of the UAS followed by histochemical and immunocytochemica l staining. Here, we present the results of this screen and the charac terization of GAL4 lines that show distinct patterns of gene expressio n during Drosophila development, including embryogenesis, oogenesis, a nd imaginal disc development. However, we were unable to identify GAL4 lines that were expressed within the germ line or during early embryo genesis. Furthermore, consistent with previous results, we found that the GAL4 enhancer trap technique had a much lower frequency of transpo sition than has been reported for lacZ enhancer trap screens. Taken to gether, these results demonstrate both the strengths and weaknesses of the GAL4 enhancer trap technique for identifying unique patterns of g ene expression during development.