ΦC31 integrase mediates efficient cassette exchange in the zebrafish germline.

Site-specific recombinases (SSRs) are powerful tools for genome manipulation, used in diverse organisms including Drosophila melanogaster, mouse, Arabidopsis, zebrafish, and human cultured cells. The integrase from the bacteriophage ΦC31 belongs to the large serine family of integrases, and in contrast to other widely used SSRs such as Cre and Flp, recombination is directional and therefore irreversible. We have developed a vector system for recombinase-mediated cassette exchange (RMCE) in the zebrafish, allowing swapping of the coding sequence in an integrated transgene. Utilizing codon-optimized ΦC31 integrase RNA bearing the 3'UTR from the nanos1 gene, we replaced the egfp coding sequence of an integrated reporter transgene with mCherry coding sequence. Recombination was achieved at high efficiency in both somatic cells and in the germline. We demonstrate an effective approach to RMCE, increasing the repertoire of tools available to manipulate the zebrafish genome.