Figure 6.

Binary Co-Driver and Co-InCre recombinase systems for sequential and coincidental conditional transgenesis. The binary recombinase components are expressed using two promoters with distinct expression profiles (red and cyan arrows, top right). Hypothetical temporal sequences of promoter activities within two distinct developmental stages of a cell lineage are shown on the left. Once activated, Cre recombinase processes a generic loxP-flanked responder sequence (dark gray box, processing is indicated by a linear and a circular reaction product), which could either represent a floxed exon leading to gene ablation or a floxed STOP cassette resulting in expression of a transgene. Non-overlapping expression patterns (A, B) result in recombination of loxP sites by Co-Driver only when Dre is expressed first (A). Both Co-Driver and Co-InCre yield recombination of loxP sites in the case of coincidental promoter activation with similar (C) or different (D, E) durations of transcription from the individual promoters.