1 Department of Laboratory Medicine and Pathology, School of Medicine, University of Washington, Box 357470, Seattle, WA, 98195-7470, USA.
2 Department of Biology and Biotechnology, University of Houston-Clear Lake, Houston, TX, USA.
3 Department of Oral Health Sciences, School of Dentistry, University of Washington, Seattle, WA, USA.
4 Department of Cell Systems and Anatomy, University of Texas Health Sciences Center, San Antonio, TX, USA.
5 Sam and Ann Barshop Center for Longevity and Aging Studies, University of Texas Health Science Center, San Antonio, TX, USA.
6 Department of Biology, University of Washington, Seattle, WA, USA.
7 Department of Laboratory Medicine and Pathology, School of Medicine, University of Washington, Box 357470, Seattle, WA, 98195-7470, USA. kaeber@uw.edu.