FIGURE 1.

Mouse genetic models for labeling intrinsically photosensitive Retinal Ganglion Cells (ipRGCs). (a) In wildtype mice, expression of melanopsin is under control of the opn4 gene. (b) Opn4-GFP mice have been genetically modified by a transgene delivered by a bacterial artificial chromosome in which the melanopsin gene has been replaced with one coding for the fluorescent reporter eGFP. (c) Opn4^cre mice have the cre gene knocked into the opn4 gene locus so that Cre is expressed under the control of the melanopsin promoter. Cre can trigger permanent recombination in a number of reporters, leading to persistent expression of the Cre-dependent reporter through the lifetime of the animal. (D–G) Cre-dependent reporters: (d) The Z/EG reporter expresses eGFP after recombination under control of the B-Actin promoter. (e) The Ai9 reporter, knocked into the highly efficient Rosa 26 locus, expresses tdTomato after recombination under control of the CAG promoter. (f) The Ai14 reporter is a variant of the Ai9 reporter with the neomycin cassette removed, leading to less labeling in the absence of Cre. (g) AAV2-EF1α-DIO-ChR2-mCherry labels infected Cre-expressing cells with the ChR2-mCherry fusion protein, which is localized to the membrane of neurons.