A. The mouse Dbp locus was modified by CRISPR-mediated insertion of the donor construct shown. The construct contained homology arms from the Dbp locus (gray and black) and inserted the reporter sequences with a T2A-encoding sequence (orange) between DBP and the reporter. Destabilized EGFP (d2EGFP) with a bovine growth hormone polyadenylation site (PA) was flanked by loxP sites (red). Downstream of GFP is a luciferase (Luc2) reporter gene. Without recombination Dbp and GFP are expressed as a single transcript from the conditional (DbpKI allele).
B. With Cre-mediated recombination, GFP-encoding sequences are excised and Dbp and luciferase are expressed as a single transcript. The T2A sequence generates separate proteins from these bifunctional transcripts. Cre-mediated germline recombination led to mice expressing luciferase non-conditionally from the DbpLuc allele.