Figure 1. Expression of GCaMP3 in various cell populations in the Ai38 mouse. A, Schematic of the gene targeting strategy to generate the Ai38 reporter mice. GCaMP3-containing Cre reporter cassette (shown in between the dashed red lines) was targeted to the ROSA26 locus in the intron between endogenous exons 1 and 2. Locations of the 5′ and 3′ arms (1.1 and 4.3 kb, respectively) for homologous recombination are indicated by the black bars. Genotyping primers are located in the GCaMP3 sequence, as indicated by the open arrows (the F and R primers). Correct gene targeting was confirmed by Southern blot (top right, lanes 1–2) using the ROSA26 locus-specific probe (the R probe) immediately upstream of the 5′ arm on HindIII (H)-digested genomic DNA, which gives rise to a 4.5 kb band for the wild-type (WT) locus and a 5.6 kb band for the gene-targeted locus. Lane 1, HindIII on WT ES cell DNA. Lane 2, HindIII on Ai38 mouse tail DNA. The single-copy integration of the transgene was confirmed by the appearance of a single band in Southern blot (top right panel, lanes 3–6) using the GCaMP3-specific probe (the G probe) on StuI/BclI- or StuI/SapI-digested genomic DNA, which gives rise to a 5.9 kb or a 5.8 kb band, respectively. Lane 3, StuI/BclI on WT ES cell DNA. Lane 4, StuI/SapI on WT ES cell DNA. Lane 5, StuI/BclI on Ai38 mouse tail DNA. Lane 6, StuI/SapI on Ai38 mouse tail DNA. B, Native fluorescence of GCaMP3 in a coronal cortical section from a Wfs1-Tg2-CreERT2:Ai38 mouse. C, GCaMP3 fluorescence in a cortical section of a Emx1-Cre:Ai38 mouse. D, Pcp2-Cre:Ai38 mouse expressing GCaMP3 in cerebellar Purkinje cells, native GCaMP3 fluorescence. E, GCaMP3 fluorescence near the AAV-syn-Cre injection site in the cortex of an Ai38 mouse. F, Pvalb-2A-Cre:Ai38 mouse expressing GCaMP3 in retinal ganglion cells. The retina was radially incised to permit flattening on a microscope glass slide for confocal microscopy. Green, GCaMP3; blue, DAPI. Radial blood vessels (black) are visible, converging on the optic disk (center). Right, Z-projection of confocal stack through the fiber and ganglion cell layers (higher magnification of the boxed area). The image shows GCaMP3-expressing ganglion cells and bundles of GCaMP3-positive axons (arrows), oriented toward the optic disk. G, Ai38 crossed with Chat-Cre targets GCaMP3 expression to SACs. Left, Maximum intensity projection of a confocal stack through the ganglion cell layer (GCL), inner plexiform layer (IPL), and inner nuclear layer (INL) of a whole-mount retina (age P8). Inset, Single z-plane through somata of SACs in the INL. Right, Confocal image of a side-on view of the same retinal slice.