Most known cancer suppression genes and mutations shorten life in laboratory mice, as they suppress the mechanisms of cell replication needed to maintain tissues. There are exceptions that have emerged as researchers find more sophisticated methods of genetic engineering to work around these limitations, but this life-extending example of gene engineering seems to be more straightforward than most: "Mice with an extra dose of a known anti-cancer gene lose weight even as their appetites grow. Not only that, but [the] animals also live longer, and that isn't just because they aren't getting cancer, either. ... One of the animals' youthful secrets is hyperactive brown fat, which burns energy instead of storing it. The findings add to evidence that tumor suppressors aren't designed only to protect us against cancer, the researchers say. They also point to new treatment strategies aimed to boost brown fat and fight aging. ... Tumor suppressors are actually genes that have been used by evolution to protect us from all kinds of abnormalities. ... In this case, the researchers studied a tumor suppressor commonly lost in human cancers. Mice with an extra copy of the gene known as Pten didn't get cancer, but that's not the half of it. Those mice were also leaner, even as they ate more than controls ... That suggested that the animals were experiencing some sort of metabolic imbalance - and a beneficial one at that. Cancer protection aside, the animals lived longer than usual. They were also less prone to insulin resistance and had less fat in their livers. Those benefits seem to trace back to the fact that those Pten mice were burning more calories thanks to overactive brown fat."