RET and retinal degeneration: To assay whether the transgenic bEF−GCAP2 protein has the capacity to activate Ret-GC activity in retinal extracts from mice in a similar manner as in in vitro studies we performed guanylate cyclase activity assays in retinal extracts from the mutant or control mice obtained prior to significant retinal degeneration -between p20 and p30 - under conditions of 0 Ca2+ or 2 μM Ca2+ (Fig. 3).