MOE Key Laboratory of Bioinformatics, Bioinformatics Division and Center for Synthetic & Systems Biology, TNLIST, Department of Automation, Tsinghua University, Beijing 100084, China, Department of Computer Science and Engineering, University of California, Riverside, CA 92521, USA, Department of Statistics, Stanford University, Stanford, CA 94305, USA MOE Key Laboratory of Bioinformatics, Bioinformatics Division and Center for Synthetic & Systems Biology, TNLIST, Department of Automation, Tsinghua University, Beijing 100084, China, Department of Computer Science and Engineering, University of California, Riverside, CA 92521, USA, Department of Statistics, Stanford University, Stanford, CA 94305, USA.