A targeting vector was designed to insert a frt-flanked neomycin resistance (neo) cassette followed by a loxP site upstream of exon 2, and a second loxP site downstream of exon 3 of the interleukin 15 receptor, alpha chain (Il15ra) gene. The construct was electroporated into C57BL/6J-derived PRX-B6T embryonic stem (ES) cells. Correctly targeted ES cells were transiently transfected with a Flpe expression plasmid to delete the neo cassette. Resulting ES cells, containing the floxed-exons, were injected into blastocysts and progeny were crossed to remove the Flp-expressing transgene (see SNP note below). Upon arrival, mice were bred to C57BL/6J inbred mice (Stock No. 000664) for at least one 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 mixed C57Bl6J;C57BL/6N genetic background.
