blood from a young mouse--or even just a factor known as GDF11 from young mouse blood--can rejuvenate the muscles and brains of older mice. The findings have led to a clinical trial in which Alzheimer's patients are receiving plasma from young donors.

engineered E. coli that harbors two additional nucleotides--X and Y--in addition to the normal G, T, C, and A that make up the standard building blocks of DNA. Such synthetic bacteria can't reproduce outside the laboratory, but they may be used to create designer proteins with "unnatural" amino acids.