Split-Creert2: Temporal Control Of Dna Recombination Mediated By Split-Cre Protein Fragment Complementation

Background: DNA recombination technologies such as the Cre/LoxP system advance modern biological research by allowing conditional gene regulation in vivo. However, the precise targeting of a particular cell type at a given time point has remained challenging since spatial specificity has so far depended exclusively on the promoter driving Cre recombinase expression. We have recently established split-Cre that allows DNA recombination to be controlled by coincidental activity of two promoters, thereby increasing spatial specificity of Cre-mediated DNA recombination. To allow temporal control of split-Cre-mediated DNA recombination we have now extended split-Cre by fusing split-Cre proteins with the tamoxifen inducible ERT2 domain derived from CreERT2.Methodology/Principal Findings: In the split-CreERT2 system, Cre-mediated DNA recombination is controlled by two expression cassettes as well as the time of tamoxifen application. By using two independent Cre-dependent reporters in cultured cells, the combination of NCre-ERT2+ERT2-CCre was identified as having the most favorable properties of all constructs tested, showing an induction ratio of about 10 and EC50-values for 4-hydroxy-tamoxifen of 10 nM to 70 nM.Conclusions/Significance: These characteristics of split-CreERT2 in vitro indicate that split-CreERT2 will be well suited for inducing DNA recombination in living mice harboring LoxP-flanked alleles. In this way, split-CreERT2 will provide a new tool of modern genetics allowing spatial and temporal precise genetic access to cell populations defined by the simultaneous activity of two promoters.