Enhancer Trap

The enhancer trap method is a molecular biological method to produce transgenic organisms which express a transgene only in particular cell without it thereby being necessary to know promoters which would be specific for this cell type. For this purpose, a GAL4 construct is introduced by means of a transposable element (enhancer - trap member) at a random position into the genome of the target organism. Thereby it jumps in the vicinity of the enhancer region of a gene, both of this gene and the GAL4 gene is activated by the enhancer. Since the specificity of the gene expression may be dependent upon the enhancer, obtained as different transgenic lines with a GAL4 expression in various cell lines.

The functional GAL4/UAS-System can then be generated by the additional introduction of a reporter gene to the UAS element in the promoter or the intersection of two tribes. A strain in this case contains the GAL4 construct ( line driver ), a second strain contains the UAS sequence ( responder line). The progeny contain in all cells and the GAL4 UAS sequences, wherein the said UAS downstream gene is expressed only in cells in which GAL4 is also active. The advantage of the system lies in the combinatorics of a large number of known GAL4 lines with UAS -linked gene constructs. The GAL4 driver line determines the location of the expression, while the UAS line defines the product.

The enhancer trap element contains inverted repeats of the P- element, the GAL4 gene, a marker gene, such as the white gene, used to identify the transformants, a polylinker sequence ( containing a variety of 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.