Enhancer trap
The enhancer trap method is a molecular biological method to generate transgenic organisms that express a transgene only in certain cells without it being necessary to know promoters that are specific for this cell type. For this purpose, a GAL4 construct is introduced into the genome of the target organism at a random location with the help of a transposable element (enhancer trap element) . If it jumps into the vicinity of the enhancer region of a gene, the enhancer activates both this gene and the GAL4 gene. Since the specificity of the gene expression can depend on the enhancer, different transgenic lines are obtained with GAL4 expression in different cell lines.
The functional GAL4 / UAS system can then be generated by additionally introducing a reporter gene with the UAS element in the promoter or by crossing two strains. One strain contains the GAL4 construct (driver line), a second strain contains the UAS sequence (responder line). The progeny contain the GAL4 and UAS sequences in all cells, the gene downstream of the UAS being expressed only in cells in which GAL4 is also active. The advantage of the system lies in the combination of a large number of known GAL4 lines with UAS-coupled gene constructs. The GAL4 driver line determines the location of the expression, while the UAS line determines the product.
The enhancer trap element contains the inverted repeats of the P element, the GAL4 gene, a marker gene such as e.g. B. the white gene, to identify the transformants, a polylinker sequence (contains various restriction sites) and an E. coli plasmid, for cloning of flanking genomic DNA. The plasmid contains an ORI (origin of replication) and an ampicillin resistance cassette.