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

Objective: Uncoupling protein 1 (UCP1), a mitochondrial protein responsible for nonshivering thermogenesis in adipose tissue, serves as a distinct marker for thermogenic brown and beige adipocytes. mice 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.

Methods: We employed mice crossed with Cre-inducible transgenic reporter Nuclear tagging and Translating Ribosome Affinity Purification (NuTRAP) mice, to investigate - expression in various tissues of adult female mice and developing embryos. Tamoxifen-inducible mice 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 and -driven reporter expression. We also investigated the impact of UCP1 deficiency on mammary gland development and function using -knockout (KO) mice.

Results: expression was observed in the mammary glands within the inguinal white adipose tissue of female ; NuTRAP mice. However, endogenous was not actively expressed as failed to induce the reporter expression in the mammary glands. was 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, -KO female mice displayed normal mammary gland development and function.

Conclusions: Our findings reveal widespread expression in various non-adipose tissue types, starting during early development. These results highlight the importance of exercising caution when interpreting data and devising experiments involving mice.