Fig. 1 In vivo FLPe-mediated target gene excision. a, b, The ACTB: FLPe transgene contains a 3.9-kb ACTB fragment inserted into a FLPe expression vector. The indicator transgene Hmgcr: FRTZ contains a 4.5-kb fragment from pHMG∆ H3 (ref. 8) inserted into pFRT2neo. lacZ (ref. 7). Rectangles, exons; heavy lines, introns and flanking regulatory sequences; arrows, translational start sites; half arrows, primers. c–f, PCR amplification detects recombination in DNA isolates from ACTB: FLPe; Hmgcr: FRTZ double-transgenic embryos (10.5 dpc). Lanes 1–7, amplification from F1 embryo DNA; lanes 8, 9, parental tail DNA. Primer pairs are indicated to the right and illustrated in (b). c, Detection of unrecombined Hmgcr: FRTZ. d, Unrecombined Hmgcr: FRTZ (top band) and recombined