Figure 1.

Targeting of the efnb1 locus. (A) Wild-type efnb1 locus (panel a) was targeted by homologous recombination of a targeting vector (panel b) carrying exons 2–5 of efnb1 gene flanked by loxP sites (triangles) and a positive selection cassette flanked by FRT sites (diamonds). The conditional allele (lox; panel c) is recombined in the presence of the Cre recombinase, producing a null allele (del; panel d). (B) Tail DNA from P10 pups was analyzed by Southern blot analysis in order to confirm proper targeting and recombination in the presence of the Cre recombinase (XbaI digest with a probe indicated in gray in panels c and d). Restriction digests of DNA from first-generation pups (panel a) as well as second-generation pups (panels b,c) are presented. (C) Western blot analysis showing loss of ephrin-B1 at the protein level in homozygous null E10.5 embryos (–/–), and decreased levels of ephrin-B1 in heterozygous embryos (+/–), as compared with wild-type (Y/+) littermates. Nonspecific bands are indicated (asterisks).