Comparative Evaluation of Sox9-CreERT2 and Aldh1l1-CreERT2 for Region-Specific Astrocyte Targeting in the Adult Mouse BrainLahoti, Esha NeuroscienceAstrocyte specificityCreERT2 mouse modelsSox9Aldh1l1Regional heterogeneityBiologyB SAstrocytes are essential regulators of synaptic transmission, ion homeostasis, and neurovascular coupling, and selective genetic access to this cell type is critical for studying its contribution to neural circuit function and disease. Inducible Cre-based transgenic mouse lines crossed with Cre-dependent fluorescent reporter strains are the primary tool for achieving temporally-restricted, cell-type-specific labeling of astrocytes in vivo, yet the specificity of available lines across brain regions has not been comprehensively characterized. This study compared the labeling specificity of two astrocyte-targeting mouse lines, Sox9-CreERT2 and Aldh1l1-CreERT2, both crossed with the Ai14 Lox-STOP-Lox-tdTomato reporter, following tamoxifen induction in adulthood. Off-target recombination was assessed by immunohistochemical co-localization of tdTomato with markers for microglia (Iba1), oligodendrocytes (Olig2), and neurons (NeuN) across three archetypical brain regions: primary motor cortex (M1), caudate-putamen (CPu), and hippocampal CA1. When data were pooled across regions, Sox9-CreERT2 showed significantly lower overlap with both microglia (3.7% vs. 8.5%, Chi-Square p=0.046) and oligodendrocytes (13.3% vs. 22.9%, p=0.0002) compared to Aldh1l1-CreERT2, with no significant difference in neuronal overlap between lines. Regional analysis revealed that the oligodendrocyte specificity advantage of Sox9-CreERT2 was driven primarily by CA1, where Aldh1l1-CreERT2 showed 23.9% oligodendrocyte overlap compared to 1.8% in the Sox9 line (p<0.00001). These findings demonstrate that Sox9-CreERT2 is a more specific astrocyte-targeting tool than Aldh1l1-CreERT2, with the advantage most pronounced in the hippocampus. The results underscore the importance of multi-region validation when characterizing genetic tools for glial research and provide a quantitative reference for selecting between these lines when labeling specificity is a priority.Grayson Oren Sipe, Thesis SupervisorBenoit A Dayrat, Thesis Honors Advisoropen_access2026-04-14T01:52:25Zhttps://honors.libraries.psu.edu/catalog/10249epl5382