Fig. 1

Experimental design. A Structure of the mouse Igf2/H19 locus. The expression of paternal Igf2 and maternal H19 genes depends on the shared 3′ enhancer. The H19 ICR, located approximately at − 4 to − 2 kb relative to the transcription start site of H19 gene is contained within a 2.9-kb SacI (Sa)-BamHI (B) fragment. Dots (1–4) and a filled box in H19 ICR indicate CTCF-binding sites and the “b” region, respectively. G; BglII site. B Structure of the 150-kb human β-globin locus YAC. The LCR and β-like globin genes are denoted as gray and filled boxes, respectively. The H19 ICR (2.9-kb H19 ICR, 2.4-kb ICR’ and ICR4321S) or lambda (lambda, LCb and LCb478) fragments were introduced 3′ to the LCR. Their methylation states after paternal (pat.) or maternal (mat.) transmission determined in our previous studies [16, 17, 20, 23] are summarized on the right. YAC–TgM carrying the LCb/LCb478 fragments were generated in this study. The different pairs of loxP sites (loxP [gray]/loxP5171 [solid]/loxP2272 [open]) are shown as triangles. C Long-range structural analysis of the LCb–LCb478 YAC transgene. The expected SfiI restriction enzyme fragments (thick lines) and probes (filled rectangles) are shown. The enlarged map shows tandemly arrayed LCb and LCb478 fragments, inserted 3′ to the LCR for employing co-placement strategy [24]. DNA from thymus cells was digested with SfiI in agarose plugs and separated by pulsed-field gel electrophoresis, and Southern blots were hybridized separately to probes. D In vivo Cre-loxP recombination to derive LCb or LCb478 TgM. Recombination between two loxP5171 sites (solid) in the parental LCb–LCb478 transgene, for example, would generate LCb478 allele, during which one of the loxP2272 sites (open) is concomitantly removed to prevent further recombination. Tail DNA from parental and daughter YAC–TgM sublines was digested with NcoI and analyzed by Southern blotting using the probe