A targeting vector containing an IRES-CreERT2 cassette (IRES, CreERT2 (Cre recombinase fused to a G400V/M543A/L544A triple mutation of the human estrogen receptor ligand binding domain), FRTsite flanked NEO, and PolyA signal) was inserted into the 3' UTR region of exon 4 of the Dbx1 gene.
This construct was electroporated into (129X1/SvJ x 129S1/Sv)F1-Kitl+
derived R1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts. The resulting chimeric mice were bred with 129S9/SvEvH (129/SvEv) mice. Mutant mice were then crossed to ROSA26::FLPe knock in mice on the 129S4/SvJaeSor genetic background; (Stock No. 003946) to remove the neo selection cassette.
The donating investigator reported that the mice were then backcrossed to 129S9/SvEvH for approximately 15 generations (see SNP note below). Upon arrival, sperm was cryopreserved. To establish our live colony, an aliquot of frozen sperm was used to fertilize 129S1/SvImJ oocytes (Stock No. 002448).
A 33 SNP (single nucleotide polymorphism) panel analysis, with 28 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. Seven of the markers (on chromosome 1, 2, 6, 8, 16, and X) were found to be segregating with a C57BL/6 genetic background. These data suggest the mice sent to The Jackson Laboratory Repository were on a mixed 129;B6 genetic background.
