These Thy1-Brainbow 1.1 (line M) transgenic mice are viable and fertile. The mice possess multiple fluorescent protein sequences uniquely flanked with pairs of incompatible Lox sites alternated to create mutually exclusive recombination events; allowing stochastic expression of multiple fluorescent proteins from a single transgene. Although the fluorescent protein immediately adjacent to the promoter, Kusabira-Orange (kOFP), was designed to be expressed prior to Cre-mediated recombination, basal kOFP expression is not observed in mouse tissues. When bred to Cre recombinase expressing mice, however, the resulting offspring can have one of three expression outcomes for each transgene in each cell of the cre expressing tissue(s): mCerulean (CFP), mYFP, or mCherry (RFP). The resulting fluorescent protein expression is observed in astrocytes of all areas of the brain and spinal cord, as well as dentate gyrus granule cells. A palmitoylation sequence tethers the mCherry (RFP), mYFP, and mCerulean (CFP) to the membrane, allowing clear labeling of axonal processes. Integration of tandem transgene copies yields combinatorial fluorescent protein expression in each cell, and thus many possible cell colors, providing a way to distinguish adjacent neurons and visualize other cellular interactions. Of note, the single FRT site inserted in the transgene allows tandem transgene copy number reduction through Flp-mediated recombination if desired. These Brainbow 1.1 (founder line M) mice allow mutually exclusive expression of three membrane-targeted fluorescent proteins in astrocytes (including glia) throughout the brain, providing unambiguous delineation of boundaries between adjacent astrocytes in cre recombined cells, and may also be useful in conjunction with other Brainbow strains (Stock No. 007901, 007910, and 007921) for neurobiological studies. The Jackson Laboratory 2024, used with permission.