Author contributions
Yi-Hui Zhang and Hai-Lei Zheng designed the experiments. Zhi-Jun Shen,
Kabir Ghoto, Gui-Feng Gao, Peng-Fei Li, Mei-Rong Luo, Zan Li, Zhi-Zhu
Zhao and Yi-Hui Zhang performed the experiments. Zhi-Jun Shen, Kabir
Ghoto and Yi-Hui Zhang analyzed the data. Zhi-Jun Shen and Yi-Hui Zhang
wrote the paper. Yi-Hui Zhang and Hai-Lei Zheng revised this paper. All
authors have read and approved the manuscript.