A FRT site flanked targeting vector containing Kan/Neo selection cassette with an upstream loxP site was utilized in the construction of this mutant. This selection cassette was inserted upstream of exon 2 of the targeted gene, and another loxP site was inserted downstream of exon 2. This construct was electroporated into 129P2/OlaHsd-derived E14Tg2a.4embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts. The resulting chimeric animals were crossed to Meox2-Cre mice to excise exon 2. The donating investigator reported that mice were backcrossed to C57BL/6 mice for 7 generations (see SNP note below). Upon arrival at The Jackson Laboratory, the mice were crossed to C57BL/6J (Stock No. 000664) at least once 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.
