Gene targeting of the Gtl2 upstream region. A) Schematic representation of the Gtl2 upstream region and the Gtl2Δ5'Neo and Gtl2Δ5' targeted loci. The targeting event replaces a 2.8-kb region of Gtl2 upstream sequence with the Neo gene (Gtl2Δ5'Neo allele). Cre-mediated excision removes the Neo gene, leaving a single loxP site in the locus (Gtl2Δ5' allele). The black boxes represent the Gtl2 exons (only exons 1–5 are shown), the gold box represents the Gtl2 DMR, the green box represents the Neo gene, the purple boxes represent highly conserved regions across species and the vertical arrow indicates the position of the Gtl2lacZ integration. B) Growth curves of Gtl2Δ5'NeoPat129 mice in comparison to wild type littermates (WT, n = 4, Gtl2Δ5'NeoPat129, n = 8). C) Growth curves of Gtl2Δ5'NeoPatB 6mice in comparison to wild type littermates (WT, n = 11, Gtl2Δ5'NeoPatB 6, n = 5). In all graphs the solid line represents wild type animals and the dashed line represents Gtl2Δ5'Neo animals.