A Mouse Built to Mark Brown Fat and Little Else

Researchers at the Pennington Biomedical Research Center have built a mouse line that lets a laboratory switch genes on or off in brown fat cells with far less stray activity elsewhere than the lines in common use.

Brown fat burns calories to make heat. The usual way to study it is to tie a genetic switch called Cre to UCP1, the gene behind that heat production, so that only those cells are altered. Writing in Scientific Reports on Oct. 22, 2026, the group reports that the widely used versions of that tool also turn on in the hypothalamus, the brain area that helps control appetite and temperature, and in other organs, which has raised concerns about how specific they are.

In the new line, named UCP1-IRES-Cre, the switch sits inside the animal's own UCP1 gene and runs off that gene's own controls. Joshua Meyer, Jaclyn Williams, senior author Heike Münzberg and three colleagues, all at Pennington Biomedical in Baton Rouge, La., crossed the mice with a reporter strain whose cells glow red wherever the switch has been active. They compared it with staining for the UCP1 protein in fat, brain and other tissue, in males and females.

The authors report that the red signal closely followed the UCP1 protein in brown and white fat, and was very limited in the hypothalamus and other organs. Set against what earlier studies reported for the older lines, the authors call the stray activity substantially reduced. One off-target site remained: the marker was strongly active in the choroid plexus, the tissue that makes the fluid around the brain, although no UCP1 protein could be stained there. In fat, the marked area was broader than the protein staining, which the authors read as cells where the gene had been active earlier.

The paper reports where the marker appears and nothing about weight, body temperature or disease. The authors offer the line as an alternative tool for work on heat-producing fat cells. Funding came in part from the National Institutes of Health, and the paper is open access.