A targeting vector containing a 12Kb fragment of mouse genomic Adar DNA and a loxP-flanked PGKneo cassette was placed within intron 11. A third loxP site was inserted within the 3'-UTR. The construct was electroporated into (129X1/SvJ x 129S1/Sv)F1 derived R1 embryonic stem (ES) cells. Transient Cre expression in targeted cells excised the neo cassette leaving loxP sites in intron 11 and downstream of exon 15. Correctly targeted ES cells were injected into blastocysts. The donating investigator reported that the resulting chimeric animals were crossed to C57BL/6 and offspring were backcrossed to C57BL/6J for 10 generations (see SNP note below). Upon arrival, mice were bred to C57BL/6J for at least 1 generation to establish the colony.
A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the rederived living colony at The Jackson Laboratory Repository. While the 27 markers throughout the genome suggested a C57BL/6 genetic background, all 5 markers that determine C57BL/6J from C57BL/6N were found to be segregating. These data suggest the mice sent to The Jackson Laboratory Repository were on a C57BL/6N genetic background.
