title: The roles of FGF and MAP kinase signaling in the segregation of the epiblast and hypoblast cell lineages in bovine and human embryos.
abstract: At the blastocyst stage of mammalian pre-implantation development, three distinct cell lineages have formed: trophectoderm, hypoblast (primitive endoderm) and epiblast. The inability to derive embryonic stem (ES) cell lines in a variety of species suggests divergence between species in the cell signaling pathways involved in early lineage specification. In mouse, segregation of the primitive endoderm lineage from the pluripotent epiblast lineage depends on FGF/MAP kinase signaling, but it is unknown whether this is conserved between species. Here we examined segregation of the hypoblast and epiblast lineages in bovine and human embryos through modulation of FGF/MAP kinase signaling pathways in cultured embryos. Bovine embryos stimulated with FGF4 and heparin form inner cell masses (ICMs) composed entirely of hypoblast cells and no epiblast cells. Inhibition of MEK in bovine embryos results in ICMs with increased epiblast precursors and decreased hypoblast precursors. The hypoblast precursor population was not fully ablated upon MEK inhibition, indicating that other factors are involved in hypoblast differentiation. Surprisingly, inhibition of FGF signaling upstream of MEK had no effects on epiblast and hypoblast precursor numbers in bovine development, suggesting that GATA6 expression is not dependent on FGF signaling. By contrast, in human embryos, inhibition of MEK did not significantly alter epiblast or hypoblast precursor numbers despite the ability of the MEK inhibitor to potently inhibit ERK phosphorylation in human ES cells. These findings demonstrate intrinsic differences in early mammalian development in the role of the FGF/MAP kinase signaling pathways in governing hypoblast versus epiblast lineage choices.
authors.affiliation: Hubrecht Institute-Royal Netherlands Academy of Arts and Sciences and University Medical Center Utrecht, Uppsalalaan 8, Utrecht, The Netherlands.
authors.forename: Ewart W
authors.initials: EW
authors.lastname: Kuijk
authors.forename: Leni T A
authors.initials: LT
authors.lastname: van Tol
authors.forename: Hilde
authors.initials: H
authors.lastname: Van de Velde
authors.forename: Richard
authors.initials: R
authors.lastname: Wubbolts
authors.forename: Maaike
authors.initials: M
authors.lastname: Welling
authors.forename: Niels
authors.initials: N
authors.lastname: Geijsen
authors.forename: Bernard A J
authors.initials: BA
authors.lastname: Roelen
mesh_terms: D000818:Animals; D002417:Cattle; D019070:Cell Lineage; D004622:Embryo, Mammalian / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051519:Fibroblast Growth Factor 4 / Q000494:pharmacology*; D050991:GATA4 Transcription Factor / Q000378:metabolism; D050993:GATA6 Transcription Factor / Q000378:metabolism; D005855:Germ Layers / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors; D000071679:Glycogen Synthase Kinase 3 beta; D006493:Heparin / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000378:metabolism; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000071317:Nanog Homeobox Protein; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011509:Proteoglycans / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D017468:Receptors, Fibroblast Growth Factor / Q000037:antagonists & inhibitors; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors
chemical_list: D051519:Fibroblast Growth Factor 4; D050991:GATA4 Transcription Factor; D050993:GATA6 Transcription Factor; D018398:Homeodomain Proteins; C486780:NANOG protein, human; D000071317:Nanog Homeobox Protein; D011509:Proteoglycans; D017468:Receptors, Fibroblast Growth Factor; D018125:Receptors, Transforming Growth Factor beta; D006493:Heparin; D000071679:Glycogen Synthase Kinase 3 beta; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; D000077293:Receptor, Transforming Growth Factor-beta Type I