The B6 Albino A++ model was developed by Taconic. In C57BL/6 mice, intron 1 of the agouti locus contains a retrotransposon which is responsible for the non-agouti phenotype. In the Taconic B6, the region containing this retrotransposon was replaced with a FRT-flanked neomycin-puromycin resistance cassette in C57BL/6NTac-derived ES cells via gene targeting. The constitutive knock out allele was then generated via Flp-mediated removal of the selection cassette. The Tyr mutation is a constitutive knock in of a point mutation in which a G nucleotide located at position 369 in exon 1 has been replaced with C nucleotide, resulting in an amino acid substitution at position 103 (Cys>Ser). The F3 site flanked selection marker was removed by via Flp recombinase. Mice containing the agouti and tyrosinase mutations were intercrossed, and then the line was intracrossed to homozygosity.
Use of the Taconic B6 Albino A++ in the following manner permits detection of ES cell germline transmission in a single step by coat color, with NO genotyping required!
Additionally, the germline progeny are identical to the C57BL/6 genome at all coat color loci!
Zevnik B, Uyttersprot NC, Perez AV, Bothe GW, Kern H, Kauselmann G. (2014) C57BL/6N albino/agouti mutant mice as embryo donors for efficient germline transmission of C57BL/6 ES cells. PLoS One. 2014 Mar 5;9(3):e90570.