Gene Function and Evolution, Centre for Genomic Regulation (CRG), Dr. Aiguader 88 and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.|Gene Function and Evolution, Centre for Genomic Regulation (CRG), Dr. Aiguader 88 and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.|Gene Function and Evolution, Centre for Genomic Regulation (CRG), Dr. Aiguader 88 and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.|Gene Function and Evolution, Centre for Genomic Regulation (CRG), Dr. Aiguader 88 and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.|Gene Function and Evolution, Centre for Genomic Regulation (CRG), Dr. Aiguader 88 and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.|Gene Function and Evolution, Centre for Genomic Regulation (CRG), Dr. Aiguader 88 and Universitat Pompeu Fabra (UPF), 08003 Barcelona, Spain.