title: The endogenous retrovirus ENS-1 provides active binding sites for transcription factors in embryonic stem cells that specify extra embryonic tissue.
abstract: BACKGROUND
  Long terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and extraembryonic lineages. To assess the transcriptional contribution of ERV to early developmental processes, we have characterized in vitro and in vivo the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells.
  
  
  RESULTS
  We show that Ens-1 LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors' activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog and Gata/Ets correlates with the Ens-1 gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an extraembryonic tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of Ens-1.
  
  
  CONCLUSIONS
  Our results show that Ens-1 LTR have co-opted conditions required for the emergence of extraembryonic tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, Ens-1 LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and extraembryonic fates.
authors.affiliation: Institut de Génomique Fonctionnelle de Lyon, Université de Lyon, CNRS, INRA, Ecole Normale Supérieure de Lyon, France. anne.mey@lyon.inra.fr
authors.forename: Anne
authors.initials: A
authors.lastname: Mey
authors.forename: Hervé
authors.initials: H
authors.lastname: Acloque
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Lerat
authors.forename: Sébastien
authors.initials: S
authors.lastname: Gounel
authors.forename: Violaine
authors.initials: V
authors.lastname: Tribollet
authors.forename: Sophie
authors.initials: S
authors.lastname: Blanc
authors.forename: Damien
authors.initials: D
authors.lastname: Curton
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Birot
authors.forename: M Angela
authors.initials: MA
authors.lastname: Nieto
authors.forename: Jacques
authors.initials: J
authors.lastname: Samarut
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D002642:Chick Embryo; D004279:DNA, Viral / Q000235:genetics*; D053595:Embryonic Stem Cells / Q000821:virology*; D020077:Endogenous Retroviruses / Q000235:genetics*; D011485:Protein Binding; D020079:Terminal Repeat Sequences; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D004279:DNA, Viral; D014157:Transcription Factors