A transient expression assay for tissue-specific gene expression of alcohol dehydrogenase in Drosophila.

The regulation of expression of the alcohol dehydrogenase gene of Drosophila was examined by injecting plasmids containing the gene directly into preblastoderm embryos and subsequently staining for alcohol dehydrogenase activity in somatic cells of larvae and adults. The alcohol dehydrogenase genes introduced in this manner were expressed normally in both adults and larvae; i.e., alcohol dehydrogenase activity was found exclusively in tissues where it would normally be expressed. Activity was found in some cells in more than 90% of all surviving third instar larvae, but not all cells which would normally express the enzyme were positive, presumably due to the random distribution of the injected DNA to the cells of the embryo. Regulated expression was not dependent on the vector used: tissue-specific expression was obtained from alcohol dehydrogenase genes inserted in the P-element vector, Carnegie-4; in pBR322; in pUC18; or in bacteriophage lambda. The bulk of the injected DNA was not integrated into the chromosome and appeared to persist throughout development as supercoiled and nicked circles. Using the procedure and in vitro mutagenesis, we were able to show that the alcohol dehydrogenase gene was expressed in a normal tissue-specific manner in larvae if there were 777 nucleotides of upstream information present.