A P-element vector has been constructed and used to generate lines of flies with single autosomal P-element insertions. The lines were analyzed in two ways: (1) the identification of cis-acting patterning information within the Drosophila genome, as revealed by a lacZ reporter gene within the P element, and (2) the isolation of lethal mutations. We examined 3768 independent lines for the expression of lacZ in embryos and looked among these lines for lethal mutations affecting embryonic neurogenesis. This type of screen appears to be an effective way to find new loci that may play a role in the development of the Drosophila nervous system.[Key Words: P element; lacZ; mutagenesis; cell market; Drosophila; pattern]Received May 30, 1989; revised version accepted July 11, 1989. One approach to studying development is to obtain genetic variants that are defective in some crucial step. This type of genetic analysis has been very successful in identifying virtually all of the zygotic loci required for the early stages of segmentation during embryogenesis in Drosophila melanogaster Niisslein-Volhard et al. 1984;Wieschaus et al. 1984). Besides chemical mutagenesis, transposon tagging has been used as a mutagen and allows rapid cloning of genes of interest (Bingham et al. 1981;Kidwell 1986).Recently, a scheme wherein single P elements are mobilized to new chromosomal locations has been implemented successfully (Cooley et al. 1988). The essential nature of this approach is to use two separate P elements to provide the two functions necessary for transposition. The first is a genetically marked P element that is defective in production of transposase but contains the ends required for its own transposition. The second is a P element with functional transposase activity but a much reduced likelihood for its own transposition (Robertson et al. 1988). Transposition of the marked P element then is initiated by crossing flies that carry only the marked P element to those that harbor only transposase. Insertions generated by this scheme are recovered in flies lacking tranposase activity and are therefore genetically stable.P-element vectors also have been used recently to search for cis-acting sequences which confer tissue-specific expression of a p-galactosidase [lacZ] fusion gene driven by the weak promoter of the P-element transpoPresent addresses:

We have identified ecdysone-response elements (EcREs) by studying regulation of the steroid-responsive Drosophila Eip28/29 gene. First, functional assays of deletion mutants identified large sequence regions required for the response; then a blotting method using the specifically labeled steroid receptor as probe