[1] European Bioinformat Inst, European Mol Biol Lab, Cambridge, England
[2] Univ Barcelona, Fac Biol, Dept Genet, Barcelona, Spain
[3] Wellcome Trust Sanger Inst, Cambridge, England
[4] Ctr Genom Regulat, Barcelona, Spain
[5] Univ Pompeu Fabra, Barcelona, Spain
[6] European Mol Biol Lab, Genome Biol Unit, D-69012 Heidelberg, Germany
[7] European Mol Biol Lab, Dev Biol Unit, D-69012 Heidelberg, Germany
[8] Univ Cambridge, Wellcome Trust Med Res Council Cambridge Stem Cel, Cambridge, England