The transgenic construct contains a codon-optimized flp recombinase followed by a bGH polyadenylation (polyA) sequence under the direction of the murine heat shock response element (Hspa1b, formerly Hsp70-1) promoter/enhancer sequences .Founder line A4 was then selected for consistent expression. Analysis using shallow whole-genome sequencing suggests that the transgene integrated into an intronic region of the Tcerg locus on chromosome 18, and in the opposite orientation to the surrounding region.