1. University of Pittsburgh, Laboratory Animal Resources, S1040 Biomedical Science Tower, Pittsburgh, Pennsylvania 15261, U.S.A. (e-mail: )
2. University of Pittsburgh, Department of Computational and Systems Biology, Pittsburgh, Pennsylvania 15261, U.S.A. (e-mail: e-mail: )
3. Tsinghua University, School of Medicine, Beijing, 100084 China (e-mail: )