1. Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health (C.M.-R., M.J.G., B.D.R., S.K., H.Y., M.B.), Baltimore, Maryland 21224
2. Institute of Developmental Biology, Russian Academy of Science (P.A.), Moscow, Russia
3. Department of Medicine, Johns Hopkins University (M.A.L., W.S.), Baltimore, Maryland 21205