Insights into calcium signaling and gene expression in astrocytes uncovered with 129S4 Slc1a3-2A-CreERT2 knock-in mice

AO_SCPLOWBSTRACTC_SCPLOWGenetic variation is a primary determinant of phenotypic diversity within populations. In laboratory mice, genetic variation has often been regarded as a serious experimental confounder, and thus minimized through inbreeding. However, generalizations of results obtained with inbred strains need to be made with caution. Effects of genetic background on traits need to be controlled, especially when working with complex phenotypes and disease models. Here we compared behavioral parameters of C57Bl/6 - the mouse strain most widely used for biomedical research - with those of 129S4. Our data demonstrate high within-strain and intra-litter behavioral hyperactivity in C57Bl/6. In contrast, 129S4 had relatively consistent activity levels throughout life. This consistency would be advantageous for studying neurodegeneration and aging, when mice need to be analyzed for long periods. However, the majority of mouse models and transgenic tools are on a C57Bl/6 background. We recently established six popular Cre driver lines and two Cre effector lines in 129S4. To augment this collection, we genetically engineered a Cre mouse line to study astrocytes directly in 129S4, which we describe here. For functional validation, it was crossed with two Cre effector lines, each in a different genomic locus, and showed in both cases that it was functional and astrocyte-specific. Calcium currents studied with gCaMP5g-tdTomato were more heterogenous, lasted longer and had a higher amplitude in cortical compared to hippocampal astrocytes. Translatomes studied with RiboTag revealed that some genes thought to mark neurons are also expressed in astrocytes, that genes linked to a single neurodegenerative disease have highly divergent expression patterns, and that ribosome proteins are non-uniformly expressed across brain regions and cell types.