Fig. 1. Conditional deletion of Erbb4 in the mammary gland. (A) Schematic representation of the wild-type ERBB4 locus, targeting vector, recombinant allele and CRE-deleted allele. The targeting vector replaces the coding region of exon 2 (black box) with a loxP-flanked exon 2. A frt-flanked PGK neomycin-resistance (neo) cassette (gray box) was included for positive selection, and a PGK thymidine kinase (tk) cassette (white box) was included for negative selection. The PGK-neo cassette was not removed in the CRE-deleted allele. An external genomic probe and an internal neo probe were used for screening embryonic stem cells. The position of PCR primers (1 and 2) are indicated by arrowheads. (B) Southern-based analysis of genomic DNA from embryonic stem cells. The 9 kb and 7 kb BamH1-digested fragments correspond to the targeted and wild-type allele, respectively. (C) PCR analysis of DNA extracted from tails of mice derived from matings between mice heterozygous for the wild-type (wt) allele and the recombinant (floxed) allele, showing the 350 bp wild-type band and the 400 bp floxed band. (D) Southern blot analysis showing CRE-mediated excision of Erbb4 exon 2 in mammary glands from 8-week-old nulliparous (N8wk) mice and two L12 Erbb4^Flox/FloxWap-Cre mice. The 9 kb and 6 kb BamH1-digested fragments were detected using an exon 2 probe and the internal control exon 10 probe, respectively.

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