A targeting vector was designed to insert a loxP site upstream of exon 1 followed by an frt-flanked neomycin resistance (neo) cassette, and a second loxP site downstream of exon 1 of the nuclear prelamin A recognition factor-like (Ciao3, also known as Narfl or Iop1) gene. The construct was electroporated into C57BL/6-derived EAP6 embryonic stem (ES) cells. Correctly targeted ES cells were injected into BALB/c blastocysts and resulting chimeric mice were bred to B6(Cg)-Tyrc-2J/J (Stock No. 000058). Offspring, heterozygous for this allele, were bred with C57BL/6-Tg(ACTBFlpe)2Arte mice to delete the neo cassette, and progeny were crossed to remove the Flp-expressing transgene. The donating investigator reported that the resulting mice were then backcrossed for at least 5 generations to C57BL/6 mice (see SNP note below). Upon arrival at The Jackson Laboratory, 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, 2 of 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 C57BL/6J ; C57BL/6N genetic background.
