A technique used in Drosophila to demonstrate the occurrence of enhancers that switch on genes in specific groups of cells during certain developmental periods. A reporter gene (q.v.) is used, which has a promoter that requires the assistance of an enhancer to be activated. The reporter gene, together with its “weak” promotor, is spliced into a transposable element (q.v.). In Drosophila, P elements (q.v.) are used, and these insert themselves at various chromosomal sites. When insertion occurs near an enhancer that normally activates genes in specific areas of a developing embryo, the reporter gene intercepts the signal and reports the position of the cells by its activity. In cases where the reporter is lacZ, blue pigment appears in specific cells; for example, in localized regions of the developing central nervous system. Once insertions that generate interesting staining patterns are identified, stable strains of flies carrying the insertions can be produced. Such lines are called transposants. Cytological mapping has shown that insertions occur throughout the genome. Since the enhancers are generally positioned within a few hundred base pairs of the start site of their target genes, these can be subsequently cloned and sequenced. See Chronology, 1987, O'Kane and Gehring.
Subjects: Genetics and Genomics.