Fig. 2. Generation of mouse models for ICF syndrome. (A) Maps of the Dnmt3b genomic locus, targeting vector, targeted locus, and recombined locus after exposure to Cre. The vertical bars represent the exons; arrowheads indicate the ICF mutations introduced. B, BamHI; E5, EcoRV; S1, SacI; Xb, XbaI; Sal, SalI; Sm, SmaI. (B) Maps of Dnmt3b wild-type and mutant (n=3) alleles used in this study. (C) Southern blot analysis of the different Dnmt3b alleles. Genomic DNA was digested with BamHI and hybridized with a 5' external probe indicated in A and B. (D) Immunoblot analysis of protein samples prepared from whole E12.5 embryos and ES cells with anti-Dnmt3b (upper panel), anti-Dnmt3a (middle panel) and anti--tubulin (lower panel) antibodies. The migration of Dnmt3a and Dnmt3b isoforms is indicated (arrowheads).