1. Department of Chemistry-Ångström; Division of Polymer Chemistry; Uppsala University; Uppsala 75121 Sweden
2. Center for Regenerative Medicine; State Key Laboratory of Molecular Developmental Biology; Institute of Genetics and Developmental Biology; Chinese Academy of Sciences; Beijing 100190 P. R. China
3. Institute of Applied Bioresource; College of Animal Science; Zhejiang University; Hangzhou Zhejiang 310058 P. R. China