Bioinformatics Group, Department of Computer Science, University of Freiburg, Georges-Köhler-Allee 106, 79110 Freiburg, Germany, Center for Biological Signaling Studies (BIOSS), University of Freiburg, Germany, Center for Biological Systems Analysis (ZBSA), University of Freiburg, Germany and Center for non-coding RNA in Technology and Health, University of Copenhagen, Grønnegårdsvej 3, DK-1870 Frederiksberg C, Denmark.