Stem cells divide and renew throughout life. But, that doesn’t mean they don’t age; stem cells do gradually lose their ability to renew. Now, researchers at the Salk Institute for Biological Studies have uncovered a series of biological events in the stem cells' surroundings, known as their niche, that lead to aging. The findings have implications for treatment of age-related diseases and the effectiveness of regenerative medicine. In studying flies, the researchers discovered that as the niche ages, the cells produce a microRNA known as let-7. This leads to a domino effect that flips a switch on aging by influencing a protein known as Imp, whose function is to protect another molecule, Upd, which promotes the signaling that keeps stem cells active and in contact with the niche so that they can self-renew. The researchers also demonstrated they could reverse this age-related loss of stem cells by increasing expression of Imp.