1. Department of Physiology, School of Medicine, Southern Illinois University, Carbondale, IL 62901, USA.
2. National Institute on Aging, NIH Animal Center, 16701 Elmer School Road, Poolesville, MS 20837, USA.
3. University of Michigan, 1500 East Medical Center Drive, Ann Arbor, MI 48109, USA.
4. Gerontology Research Center, 5600 Nathan Shock Drive, Baltimore, MD 21224, USA.
5. Department of Biology, University College London, Gower Street, London WC1E 6BT, UK.
6. Zoologisches Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
7. Growth Regulation Laboratory, Imperial Cancer Research Fund, Post Office Box 123, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.