Figure 2. Strategy for Cre-dependent expression of opsins.

The example shown uses the double floxed inverted open reading frame strategy. Opsin-encoding virus can be injected into a transgenic mouse expressing Cre recombinase in a molecularly defined subset of cells. In the presence of Cre recombinase, the opsin-encoding region is inverted, allowing translation into functional protein within these cells. pr, ubiquitous promoter. Adapted from ¹.