A genetic construct that reports cre recombinase activity with tauLacZ reporter gene was inserted in reverse orientation into the Gt(ROSA)26Sor safe harbor locus. The reporter construct included a CAG promoter, a loxP flanked stop cassette composed of neomycin resistance gene and multiple polyadenylation sequences, a tauLacZ reporter gene, and a polyadenylation sequence (pCAG-loxP-pEM7-Neo*-bGHpA-3xSV40pA-loxP-tauLacZ-bGHpA). The construct was electroporated into B6(Cg)-Tyrc-2J derived CY2.4 embryonic stem cells. Southern blot positive embryonic stem cell clones were injected into recipient C57BL/6J blastocysts. Positive male chimeras were bred with B6(Cg)-Tyrc-2J females. Albino pups were genotyped by PCR, then bred to B6J mice.