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Fig. 4 Molecular evidences of Cre-mediated recombination. A: Schematic representation of Tg(zlmo2:loxP-DsRed-loxP-EGFP) and Tg(zlmo2:Cre) transgenic lines used to test Cre activity. In the presence of Cre expression, DsRed is excised and expression of EGFP is initiated in double transgenic embryos. Arrows denote the positions of primers designed to detect genomic recombination by PCR. B: Detection of Cre-mediated recombination by genomic PCR. An expected 0.6-kb recombinant fragment is amplified after Cre-mediated excision using primer p1 and p2. A 0.5-kb unrecombinant fragment was also amplified using primer p1 and p3 (arrows). C,D: Sequence of the unrecombined 1.8-kb product (C) and recombined 0.6-kb product (D). Shown are sequences from around 30 bp upstream of the first loxP site to around 30 bp downstream of the ATG start codon of EGFP (circle). Dashed line between the loxP sites denotes the open reading frame of DsRed; black boxes denote the ATG start codon of DsRed; and black lines indicate the loxP sites.