Detection in situ of genomic regulatory elements in Drosophila.

We have developed an approach for the in situ detection of genomic elements that regulate transcription zin Drosophila melanogaster. The approach is analogous to a powerful method of bacterial genetics, the random generation of operon fusions, that enables the isolation and characterization of genes simply by knowing or postulating their pattern of expression; it is not necessary initially to screen for mutant phenotypes. To apply this approach to Drosophila, we have used the expression of the lacZ gene of Escherichia coli from the P-element promoter in germ-line transformant flies to screen for chromosomal elements that can act at a distance to stimulate expression from this apparently weak promoter. Of 49 transformed fly lines obtained, approximately 70% show some type of spatially regulated expression of the lacZ gene in embryos; many of these express lacZ specifically in the nervous system. The P-lacZ fusion gene is, therefore, an efficient tool for the recovery of elements that may regulate gene expression in Drosophila and for the generation of a wide variety of cell-type-specific markers.