Conditional expression of the HGAL oncogene. (A) Schematic diagram showing the HGAL cDNA cloned into a vector designed for targeting into the mouse Rosa26 locus. Cre-mediated recombination excises the STOP sequence and initiates expression of the fusion oncogene and eGFP. To prevent transcription of the fusion gene and eGFP from the Rosa26 promoter, a neomycin resistance cassette and polyadenylation STOP signal flanked by loxP sites were inserted between the promoter and the HGAL-IRES-eGFP sequence. In the absence of Cre, HGAL and eGFP are not expressed, due to a STOP cassette in front of HGAL that must be removed by Cre recombinase action to allow for their expression. Neo, neomycin resistance cassette; pA, polyadenylation STOP sequence. (B) Mouse embryonic stem (ES) cells confirmed to harbor the targeted allele were injected into blastocysts to generate chimeras that were then bred to generate progeny with a germline-transmissible conditional allele of HGAL (designated Rosa26^HGAL). Identification of Rosa26^HGAL mice by Southern blot analysis of tail snip DNA after EcoRI digestion is shown. DT, refers to the SA-PGK-neo-LacZ(DTA)-bpA fragment inserted into Rosa26 genomic locus; ex1, exon1; ex2, exon2; ex3, exon 3; frt, frt site of the FLP/FRT site-specific recombination system.