Transgenic mice carry a construct knocked into the Gt(ROSA)26Sor locus, consisting of a CAG promoter, and frt-flanked pgk-Neo cassette, a STOP cassette consisting of the terminator of the yeast His3 gene and SV40 poly-adenylation sequence37, cDNA encoding fluorescent Guillardia theta microbial rhodopsin ACR2 cDNA tagged with EYFP at the C-terminus, a woodchuck hepatitis virus post-transcriptional regulatory element, and the rabbit beta-globin poly-adenylation sequence. Two loxP sites were inserted before the frt-Neo cassette and after the STOP cassette. (J:338273)