Application of Cre/loxP in Drosophila: Site-Specific Recombination and Transgene Coplacement

The use of site-specific recombinases has revolutionized the genetic analysis of development and has made possible the precise engineering of genomes (1 ,2 ). In Drosophila , the FLP/FRT system, introduced by Golic and Lindquist (3 ), has been used (1) to generate genetic mosaics by mitotic recombination as well as by “flip-outs”(3 -5 ), and (2) to generate defined chromosomal rearrangements (6 ,7 ). In yeast and mammalian cells, site-specific recombination has also been used to mediate targeting of exogenous DNA to genomic docking sites (8 ). Although such targeted integration is by nature an inefficient process-as a result of the favoring of intramolecular over intermolecular recombination-this limitation has been overcome in these systems by the ability to introduce DNA into a large number of cells simultaneously and to select for rare integration events by chemical means. In Drosophila , such an approach is not currently available, although an approximation of targeted integration of exogenous DNA has been used, with varying efficiency, to mobilize FRT-flanked DNA already in the genome to a specific FRT target site elsewhere (9 ).