Effect of TAM treatment on gene expression profile of microglia from Cx3cr1CreERT2 mouse lines.

Microglia, the resident macrophages in the central nervous system (CNS), have been intensively studied using rodent genetic models, including the Cx3cr1-Cre mouse line. These mice have enabled the in-depth analyses of the biological features and functions of myeloid cells, including microglia. Occasionally, these Cx3cr1CreERT2 tools have yielded conflicting outcomes, the underlying mechanism of which remains unclear. Here, we comparatively characterize the two available Cx3cr1CreERT2 lines (Cx3cr1CreERT2(Litt) and Cx3cr1CreERT2(Jung)). We find a mouse line-specific and TAM-dependent persistent induction of CDKN1A in microglia of Cx3cr1CreERT2(Litt) mice, but not in those of Cx3cr1CreERT2(Jung) mice, which affects experimental readouts with altered proliferative capacity. Furthermore, aberrant cellular alterations observed in postnatal Cx3cr1CreERT2(Litt) microglia are mitigated by a functional inhibition of CDKN1A. Together, these findings underscore the significance of mouse line-specific phenomena that alter microglial outcomes in a CDKN1A-dependent manner, highlighting the importance of rigorous validation of genetic mouse tools.