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  • The EMBO Journal (1997) 16, 6250 - 6262
  • doi:10.1093/emboj/16.20.6250

Nuclear translocation and carboxyl-terminal domain phosphorylation of RNA polymerase II delineate the two phases of zygotic gene activation in mammalian embryos

Sylvain Bellier1,5, Sylvie Chastant2,3,5, Pierre Adenot3, Michel Vincent4, Jean Paul Renard3 and Olivier Bensaude1

  1. Génétique Moléculaire, URA 1302 CNRS, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Cedex 05 France
  2. Service de Reproduction, Ecole Nationale Vétérinaire, 7 Avenue du Général De Gaulle, 94704 Maisons-Alfort Cedex, France
  3. Biologie du Développement, Institut National de la Recherche Agronomique, 78352 Jouy en Josas, France
  4. Recherche en Sciences de la Vie et de la Santé, Pavillon Marchand, Université Laval, Sainte-Foy, Québec G1V 4G2, Canada
  5. S.Bellier and S.Chastant contributed equally to this work

Correspondence to:

Olivier Bensaude, E-mail: bensaude@biologie.ens.fr

Received 10 February 1997; Revised 4 August 1997

In mammalian embryos, zygotic gene transcription initiates after a limited number of cell divisions through a two-step process termed the zygotic gene activation (ZGA). Here we report that RNA polymerase II undergoes major changes in mouse and rabbit preimplantation embryos during the ZGA. In transcriptionally inactive unfertilized oocytes, the RNA polymerase II largest subunit is predominantly hyperphosphorylated on its carboxy-terminal domain (CTD). The CTD is markedly dephosphorylated several hours after fertilization, before the onset of a period characterized by a weak transcriptional activity. The largest subunit of RNA polymerase II then lacks immunological and drug-sensitivity characteristics related to its phosphorylation by the TFIIH-associated kinase and gradually translocates into the nuclei independently of DNA replication and mitosis. A phosphorylation pattern of the largest subunit, close to that observed in somatic cells, is established in both mouse and rabbit embryos at the stage when transcription becomes a requirement for further development (respectively at the 2- and 8/16-cell stage). As these events occurred in the presence of actinomycin D, the nuclear translocation of RNA polymerase II and the phosphorylation of the CTD might be major determinants of ZGA.

  • Keywords:

    • embryo,
    • phosphorylation,
    • RNA polymerase,
    • transcription