When we’re cold, we can shiver and let our muscular action heat us up. We can also have our brown fat tissues use up fats without storing energy, just liberating heat. The secret of the latter, at least in us and other “placental” mammals, is a protein called uncoupling protein 1, or UCP1. It acts by preventing the biochemical steps in our mitochondria (our energy centers “plus”) from storing energy in ATP. Neat stuff. This can’t be done by marsupial mammals that pop out offspring in tiny form rather than keeping the developing fetuses inside the mother’s body, nourished through a placenta.
Wombats, opossums, platypuses are out of luck. They do have a version of the UCP1 protein that helps mobilize fats but they have to process the fat to muscular energy to shiver and warm up. Susanne Keipert at Stockholm University (where they know about shivering!) and 14 colleagues studied metabolic details in an opossum. They also used genetic analyses of placental mammals and marsupials. They looked for the time when UCP1 in placental mammals acquired its second function, allowing simple heat generation.
Their evidence is that it evolved just around the time that placental mammals split off from marsupials, 150 million years ago. This is not just a matter of comfort. We, orcas, foxes and others have to keep our notably delicate brains warm enough to function.
This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org.
Source: Science 384: 1111-1117 (June 7, 2024)
