The "miR-17-92 transgene" was designed with (from 5' to 3') a synthetic CAG promoter, a loxP-flanked Neo-STOP cassette, a genomic DNA fragment encoding the human miR-17-92 cluster (encoding the precursor of seven miRNA molecules; miR-17-5p, miR-17-3p, miR-18a, miR-19a, miR-20a, miR-19b and miR-92), a frt-flanked internal ribosomal entry site-enhanced green fluorescent protein (IRES-EGFP), and polyadenylation signal. This transgene was inserted between exons 1 and 2 of the Gt(ROSA)26Sor locus via electroporation into C57BL/6-derived Bruce-4 embryonic stem (ES) cells. Correctly targeted ES cells were selected and chimeric animals were bred to generate mutant mice. These "miR-17-92 transgenic" mice were maintained on a C57BL/6 genetic background as a homozygous colony for many generations (see SNP note below). Upon arrival at The Jackson Laboratory, mice were bred with 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.
