title: The hypoblast (visceral endoderm): an evo-devo perspective.
abstract: When amniotes appeared during evolution, embryos freed themselves from intracellular nutrition; development slowed, the mid-blastula transition was lost and maternal components became less important for polarity. Extra-embryonic tissues emerged to provide nutrition and other innovations. One such tissue, the hypoblast (visceral endoderm in mouse), acquired a role in fixing the body plan: it controls epiblast cell movements leading to primitive streak formation, generating bilateral symmetry. It also transiently induces expression of pre-neural markers in the epiblast, which also contributes to delay streak formation. After gastrulation, the hypoblast might protect prospective forebrain cells from caudalizing signals. These functions separate mesendodermal and neuroectodermal domains by protecting cells against being caught up in the movements of gastrulation.
authors.affiliation: Department of Cell and Developmental Biology, University College London, GowerStreet (Anatomy Building), London WC1E 6BT, UK. c.stern@ucl.ac.uk
authors.forename: Claudio D
authors.initials: CD
authors.lastname: Stern
authors.forename: Karen M
authors.initials: KM
authors.lastname: Downs
mesh_terms: D000650:Amnion / Q000378:metabolism / Q000502:physiology; D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning / Q000235:genetics*; D002642:Chick Embryo; D004627:Embryonic Induction / Q000235:genetics; D004707:Endoderm / Q000196:embryology; D054262:Gastrulation; D018507:Gene Expression Regulation, Developmental; D005855:Germ Layers / Q000502:physiology*; D051379:Mice; D009420:Nervous System / Q000196:embryology; D009747:Nutritional Physiological Phenomena; D054240:Primitive Streak / Q000502:physiology