Acta2BAC-GCaMP-GR transgenic mice express the ratiometric fluorescent calcium indicator GCaMP-green/red (GCaMP-GR) under control of the Acta2 locus promoter/enhancer regions within the BAC transgene. Acta2BAC-GCaMP-GR transgenic mice from founder line 1 exhibit high sensor GCaMP-GR expression (mCherry fluorescence before calcium and EGFP fluorescence after calcium) in smooth muscle actin, including vessels. In total, transgene expression is consistent with endogenous Acta2. In the absence of calcium binding, bright mCherry fluorescence and low/baseline EGFP fluorescence is observed. Following calcium binding (such as during muscle contraction), bright EGFP fluorescence is observed. Hemizygous mice are viable with no reported gross physical or behavioral abnormalities. When maintaining our live colony, best results have been achieved breeding hemizygous females to wildtype (noncarrier) mice from the colony. To date (August 2017), it has not been attempted to make this strain homozygous. The expected coat color is white (albino) or agouti. The donating investigator reports that backcrossing onto C57BL/6 may result in decreased fertility for hemizygous males. Additionally, hemizygous males may also have decreased fertility on other genetic backgrounds.
 Calcium is a key molecular signal for cell functions including heart, smooth muscle, vessel, and airway contraction, lung secretion, autonomic neurotransmission and immunocyte function. Acta2BAC-GCaMP-GR transgenic mice may be useful to examine calcium signaling in smooth muscle electrical and chemical signaling both in vivo and in vitro. The ratiometric calcium indicator GCaMP-GR (green/red) is an optimized GCaMP3 variant (A206V, S30R, Y39N and N105T mutations in EGFP) fused to the mCherry fluorescent protein by a flexible alanine-proline repeat linker (GSSTSG-APAPAPAPAPAPAP-SEF) designed by Dr. Michael I. Kotlikoff (Cornell University; <a href="http://www.ncbi.nlm.nih.gov/pubmed/25414670">Shui et al. 2014 Front Physiol 5:428</a>). Compared to GCaMP3, GCaMP-GR has equivalent calcium sensitivity, lower resting fluorescence, higher dynamic range and calcium-independent mCherry fluorescence. GCaMP-GR allows calcium-independent bright mCherry fluorescence before calcium transients when GCaMP fluorescence is dim (as GCaMP has a pore from the outside of its barrel into the chromophore). Upon calcium binding, this pore becomes occupied and EGFP fluorescence is increased. This mouse model is available by way of a collaborative effort between Cornell/National Heart Lung Blood Resource for Optogenetic Mouse Signaling (<a href="http://chromus.vet.cornell.edu">CHROMus</a>) and The Jackson Laboratory.

Acta2BAC-GCaMP-GR transgenic mice are a fluorescent calcium indicator strain that exhibits high calcium-sensor expression in smooth muscle actin, including vessels. The ratiometric GCaMP-GR allows calcium-independent bright mCherry fluorescence when GCaMP fluorescence is dim (before calcium transients). Upon calcium binding, this pore becomes occupied and EGFP fluorescence is increased.

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