title: Intrinsic factors and the embryonic environment influence the formation of extragonadal teratomas during gestation.
abstract: BACKGROUND
  Pluripotent cells are present in early embryos until the levels of the pluripotency regulator Oct4 drop at the beginning of somitogenesis. Elevating Oct4 levels in explanted post-pluripotent cells in vitro restores their pluripotency. Cultured pluripotent cells can participate in normal development when introduced into host embryos up to the end of gastrulation. In contrast, pluripotent cells efficiently seed malignant teratocarcinomas in adult animals. In humans, extragonadal teratomas and teratocarcinomas are most frequently found in the sacrococcygeal region of neonates, suggesting that these tumours originate from cells in the posterior of the embryo that either reactivate or fail to switch off their pluripotent status. However, experimental models for the persistence or reactivation of pluripotency during embryonic development are lacking.
  
  
  METHODS
  We manually injected embryonic stem cells into conceptuses at E9.5 to test whether the presence of pluripotent cells at this stage correlates with teratocarcinoma formation. We then examined the effects of reactivating embryonic Oct4 expression ubiquitously or in combination with Nanog within the primitive streak (PS)/tail bud (TB) using a transgenic mouse line and embryo chimeras carrying a PS/TB-specific heterologous gene expression cassette respectively.
  
  
  RESULTS
  Here, we show that pluripotent cells seed teratomas in post-gastrulation embryos. However, at these stages, induced ubiquitous expression of Oct4 does not lead to restoration of pluripotency (indicated by Nanog expression) and tumour formation in utero, but instead causes a severe phenotype in the extending anteroposterior axis. Use of a more restricted T(Bra) promoter transgenic system enabling inducible ectopic expression of Oct4 and Nanog specifically in the posteriorly-located primitive streak (PS) and tail bud (TB) led to similar axial malformations to those induced by Oct4 alone. These cells underwent induction of pluripotency marker expression in Epiblast Stem Cell (EpiSC) explants derived from somitogenesis-stage embryos, but no teratocarcinoma formation was observed in vivo.
  
  
  CONCLUSIONS
  Our findings show that although pluripotent cells with teratocarcinogenic potential can be produced in vitro by the overexpression of pluripotency regulators in explanted somitogenesis-stage somatic cells, the in vivo induction of these genes does not yield tumours. This suggests a restrictive regulatory role of the embryonic microenvironment in the induction of pluripotency.
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Constantinos
authors.initials: C
authors.lastname: Economou
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Anestis
authors.initials: A
authors.lastname: Tsakiridis
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Filip J
authors.initials: FJ
authors.lastname: Wymeersch
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Gordon-Keylock
authors.affiliation: Drug Discovery Unit, Telethon Kids Institute, PO Box 855, West Perth, WA, 6872, Australia.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Dewhurst
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Dawn
authors.initials: D
authors.lastname: Fisher
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Alexander
authors.initials: A
authors.lastname: Medvinsky
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK.
authors.forename: Andrew J H
authors.initials: AJ
authors.lastname: Smith
authors.affiliation: MRC Centre for Regenerative Medicine, School of Biological Sciences, SCRM Building, The University of Edinburgh, Edinburgh bioQuarter, 5 Little France Drive, Edinburgh, EH16 4UU, UK. v.wilson@ed.ac.uk.
authors.forename: Valerie
authors.initials: V
authors.lastname: Wilson
mesh_terms: D000818:Animals; D004622:Embryo, Mammalian / Q000378:metabolism* / Q000473:pathology; D053595:Embryonic Stem Cells / Q000378:metabolism*; D005326:Fetal Proteins / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics; D006801:Humans; D051379:Mice; D000071317:Nanog Homeobox Protein; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D039904:Pluripotent Stem Cells / Q000378:metabolism; D020825:T-Box Domain Proteins / Q000378:metabolism; D013623:Tail / Q000196:embryology; D013724:Teratoma / Q000378:metabolism* / Q000473:pathology*; D000098908:Brachyury Protein
chemical_list: D005326:Fetal Proteins; D018398:Homeodomain Proteins; D000071317:Nanog Homeobox Protein; D050814:Octamer Transcription Factor-3; D020825:T-Box Domain Proteins; D000098908:Brachyury Protein; C475540:Nanog protein, mouse; C494174:Pou5f1 protein, mouse