Uncoupling protein 1-driven Cre (Ucp1-Cre) is expressed in the epithelial cells of mammary glands and various non-adipose tissues

Abstract

ABSTRACTObjectiveUncoupling protein 1 (UCP1), a mitochondrial protein responsible for nonshivering thermogenesis in adipose tissue, serves as a distinct marker for thermogenic brown and beige adipocytes.Ucp1-Cremice are thus widely used to genetically manipulate these thermogenic adipocytes. However, evidence suggests that UCP1 may also be expressed in non-adipocyte cell types. In this study, we investigated the presence of UCP1 expression in different mouse tissues that have not been previously reported.MethodsWe employedUcp1-Cremice crossed with Cre-inducible transgenic reporter Nuclear tagging and Translating Ribosome Affinity Purification (NuTRAP) mice, to investigateUcp1-Creexpression in various tissues of adult female mice and developing embryos. Tamoxifen-inducibleUcp1-CreERT2mice crossed with NuTRAP mice were used to assess active UCP1 expression. Immunostaining, RNA analysis, and single-cell/nucleus RNA-seq (sc/snRNA-seq) data analysis were performed to determine the expression of endogenous UCP1 andUcp1-Cre-driven reporter expression. We also investigated the impact of UCP1 deficiency on mammary gland development and function usingUcp1-knockout (KO) mice.ResultsUcp1-Creexpression was observed in the mammary glands within the inguinal white adipose tissue of femaleUcp1-Cre; NuTRAP mice. However, endogenousUcp1was not actively expressed asUcp1-CreERT2failed to induce the reporter expression in the mammary glands.Ucp1-Crewas activated during embryonic development in various tissues, including mammary glands, as well as in the brain, kidneys, eyes, and ears, specifically in epithelial cells in these organs. While sc/snRNA-seq data suggest potential expression of UCP1 in mammary epithelial cells in adult mice and humans,Ucp1-KO female mice displayed normal mammary gland development and function.ConclusionsOur findings reveal widespreadUcp1-Creexpression in various non-adipose tissue types, starting during early development. These results highlight the importance of exercising caution when interpreting data and devising experiments involvingUcp1-Cremice.