Stock No. 029043 is the C57BL/6J-congenic Ai38 mouse line, also called Ai38 (C57BL/6J), Ai38(RCL-GCaMP3) (C57BL/6J) or B6J.Ai38. In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. The phenotype described below is for Ai38 mice on a C57BL/6J;C57BL/6N genetic background (Stock No. <a href="https://www.jax.org/strain/014538">014538</a>). It should be noted that the phenotype of this C57BL/6J-congenic line could vary from that originally described for mice on other genetic backgrounds. We will modify the strain description if necessary as published results become available. Ai38 mice heterozygous for the Rosa-CAG-LSL-GCaMP3-WPRE conditional allele are viable and fertile. A loxP-flanked STOP cassette prevents transcription of the downstream GCaMP3 fusion gene (see below for detailed description of GCaMP3). Because the CAG promoter driven reporter construct was targeted for insertion into the Gt(ROSA)26Sor locus, GCaMP3 expression is determined by which tissue(s) express Cre recombinase. When bred to mice that express Cre recombinase, the resulting offspring will have the STOP cassette deleted in the cre-expressing tissues; resulting in expression of the fluorescent calcium indicator protein, GCaMP3. The donating investigator reports that Ai38 mice do not express GCaMP3 prior to introduction of Cre recombinase. Following exposure to Cre recombinase, GCaMP3 expression (EGFP fluorescence) is detected in the cre-expressing tissues. In the absence of calcium binding, low EGFP fluorescence is reported. Following calcium binding (such as neuronal activation) bright EGFP fluorescence is observed. GCaMP3 expression in tissues other than brain has not yet been evaluated by the donating investigator (April 2011). The phenotype of homozygous mice has not been characterized by the donating investigator. Of note, the FRT sites flanking the mutation allow for additional targeted replacement of the reporter sequences through Flp-mediated recombination if so desired. Similarly, the attB/attP-flanked selection cassette may be removed by introduction of the site-specific bacteriophage PhiC31 integrase if so desired. For characterization information, see images at the Allen Institute for Brain Science website (<a href="http://connectivity.brain-map.org/transgenic/imageseries/list/1.html?gene_term=Ai38">Ai38 images</a>). GCaMP3 is a fluorescent calcium indicator. The GCaMP3 fusion gene contains the chicken smooth muscle M13 fragment of myosin light chain kinase (MYLK), a circularly permutated EGFP sequence (with several amino acid substitutions designed to increase dynamic range and baseline fluorescence), and a rat calmodulin (Calm) sequence modified to increase the fluorescence change for small calcium transients. In the absence of calcium binding, dim EGFP fluorescence is expected as there is a pore from the outside of its barrel into the chromophore. Upon calcium binding, this pore becomes occupied and fluorescence is increased.

 Ai38 mice express the fluorescent calcium indicator protein GCaMP3 after exposure to Cre recombinase. Following subsequent calcium binding (such as neuronal activation), bright EGFP fluorescence is observed.

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B6.Cg-Gt(ROSA)26Sor<tm38(CAG-GCaMP3)Hze>/J