. Author manuscript; available in PMC: 2016 Dec 20.
Published in final edited form as: Sci China Life Sci. 2016 Feb 26;59(12):1270–1281. doi: 10.1007/s11427-015-4997-y
This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.