Figure 2. Monitoring disease activity in dysferlin-deficient mice by noninvasive bioluminescence imaging.

(A) Diagrammatic representation of the temporal pattern of luciferase expression in dystrophic Pax7Cre^ER/LuSEAP mice. After tamoxifen administration, a subset of satellite cells express luciferase. In response to injury or muscle degeneration, these luciferase-positive satellite cells activate and proliferate, giving rise to luciferase-positive myoblasts that ultimately differentiate and fuse to form new myofibers, which will then be luciferase positive. (B) Wild-type (left) and dysferlin-deficient (right) Pax7Cre^ER/LuSEAP mice, injected with tamoxifen at 2 months of age, imaged together at 7 months of age. Scale to the right of the image represents photon emission from the tissue surface and is expressed as p/s/cm²/sr (or radiance). (C) The luciferase signals from distal hind limb muscles of both wild-type and dysferlin-deficient mice were measured before tamoxifen administration (Pre-tam), at 3 months of age, and then monthly up to 18 months of age. P < 0.05 for each measurement between 3 and 18 months of age in the dysferlin-deficient compared with the control strain; n = 12 Dysf^+/+ compared with Dysf^–/– at each time point. (D) Luciferase signals from the distal hind limb muscles of male and female dysferlin-deficient mice (n = 12; same mice as in C).