Figure 2.

(A) Ratiometric GCaMP, GCaMP-GR, was created by fusing an improved GCaMP (GCaMP3 with the additional mutations shown) with mCherry, using an optimized linker. Below Ca²⁺ -dependent green fluorescence of GCaMP-GR protein relative to earlier GCaMPs. The F_max/F₀ ratio is improved in GCaMP-GR due to a lower F₀ fluorescence. (B) Targeting of GCaMP-GR in mice. Top, a smooth muscle actin bacterial artificial chromosome (ACTA2^BAC) construct was used to target GCaMP-GR. Middle, smooth muscle–specific green and red fluorescence in vascular smooth muscle, anti-GFP IHC staining. Bottom, green and red fluorescence in smooth muscle of small intestine. (C) CHROMus, the Cornell Heart, Lung, Blood Resource for Optogenetic Mouse Signaling, which will create combinatorial mouse strains.