[1] Roslin Inst, Dept Gene Express & Dev, Roslin EH25 9PS, Midlothian, Scotland
[2] Univ Edinburgh, Ctr Genome Res, Edinburgh EH9 3JQ, Midlothian, Scotland
[3] Ecole Normale Super Lyon, Lab Biol Mol & Cellulaire, CNRS, UMR 5665,INRA, F-69364 Lyon 07, France