1. CAS-MPG Partner Institute and Key Lab for Computational Biology, 320 Yue-Yang Road, Shanghai 200031, P. R. China
2. Max-Planck-Institute for Mathematics in the Sciences, Inselstrasse 22, D-04103 Leipzig, Germany
3. School of Mathematical Sciences, Fudan University, 220 Han-Dan Road, Shanghai 200433, P. R. China
4. School of Mathematical Sciences and Centre for Computational Systems Biology, Fudan University, 220 Han-Dan Road, Shanghai 200433, P. R. China