There was an error in the Funding statement. The correct version of the Funding statement is available below.
This work is funded by the grants from the Ministry of Science and Technology of China (S & T major Program: No. 2012ZX1004701-001-002), the Basic Research Program of China (973 Program, No. CB531502), the National Nature Science Foundation of China (No. 31170829, 31070783, 81021003), and Beijing Natural Science Foundation (No. 5112022). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Footnotes
Competing Interests: No competing interests declared.