The widely used Ucp1-Cre transgene elicits complex developmental and metabolic phenotypes
Manasi Halurkar, Oto Inoue, Archana Singh, Rajib Mukherjee, Meghana Ginugu, Christopher Ahn, Christian Louis Bonatto Paese, Molly Duszynski, Samantha A. Brugmann, Hee‐Woong Lim, Joan Sánchez-Gurmaches
Abstract
Bacterial artificial chromosome transgenic models, including most Cre-recombinases, enable potent interrogation of gene function in vivo but require rigorous validation as limitations emerge. Due to its high relevance to metabolic studies, we perform comprehensive analysis of the Ucp1-CreEvdr line which is widely used for brown fat research. Hemizygotes exhibit major brown and white fat transcriptomic dysregulation, indicating potential altered tissue function. Ucp1-CreEvdr homozygotes also show high mortality, tissue specific growth defects, and craniofacial abnormalities. Mapping the transgene insertion site reveals insertion in chromosome 1 accompanied by large genomic alterations disrupting several genes expressed in a range of tissues. Notably, Ucp1-CreEvdr transgene retains an extra Ucp1 gene copy that may be highly expressed under high thermogenic burden. Our multi-faceted analysis highlights a complex phenotype arising from the presence of the Ucp1-CreEvdr transgene independently of intended genetic manipulations. Overall, comprehensive validation of transgenic mice is imperative to maximize discovery while mitigating unexpected, off-target effects. UCP1 is involved in regulating thermogenesis, and the Ucp1-Cre mouse line has been widely used for studying brown fat. Here they show that this mouse line carries an extra copy of the Ucp1 gene and displays unexpected changes in fat tissue function. Researchers should be cautious when interpreting studies using this model.