[1] Univ Salamanca, Inst Biol Mol & Celular Canc, CSIC, Salamanca 37007, Spain
[2] Univ Salamanca, Dept Fisiol, Consejo Super Invest Cient, Salamanca 37007, Spain
[3] Univ Salamanca, Dept Med, Consejo Super Invest Cient, Salamanca 37007, Spain
[4] CSIC, Dept Proliferac Celular & Desarrollo, Ctr Invest Biol, Madrid 28040, Spain
[5] Cornell Univ, Ctr Vertebrate Genom, Ithaca, NY 14850 USA
[6] Univ Amsterdam, Acad Med Ctr, Ctr Reprod Med, NL-1105 AZ Amsterdam, Netherlands