title: Deployment of regulatory genes during gastrulation and germ layer specification in a model spiralian mollusc Crepidula.
abstract: BACKGROUND
  During gastrulation, endoderm and mesoderm are specified from a bipotential precursor (endomesoderm) that is argued to be homologous across bilaterians. Spiralians also generate mesoderm from ectodermal precursors (ectomesoderm), which arises near the blastopore. While a conserved gene regulatory network controls specification of endomesoderm in deuterostomes and ecdysozoans, little is known about genes controlling specification or behavior of either source of spiralian mesoderm or the digestive tract.
  
  
  RESULTS
  Using the mollusc Crepidula, we examined conserved regulatory factors and compared their expression to fate maps to score expression in the germ layers, blastopore lip, and digestive tract. Many genes were expressed in both ecto- and endomesoderm, but only five were expressed in ectomesoderm exclusively. The latter may contribute to epithelial-to-mesenchymal transition seen in ectomesoderm.
  
  
  CONCLUSIONS
  We present the first comparison of genes expressed during spiralian gastrulation in the context of high-resolution fate maps. We found variation of genes expressed in the blastopore lip, mouth, and cells that will form the anus. Shared expression of many genes in both mesodermal sources suggests that components of the conserved endomesoderm program were either co-opted for ectomesoderm formation or that ecto- and endomesoderm are derived from a common mesodermal precursor that became subdivided into distinct domains during evolution.
authors.affiliation: University of Illinois, Department of Cell and Developmental Biology, Urbana, Illinois.
authors.forename: Kimberly J
authors.initials: KJ
authors.lastname: Perry
authors.affiliation: Biology Department, Duke University, Durham, North Carolina.
authors.forename: Deirdre C
authors.initials: DC
authors.lastname: Lyons
authors.affiliation: Departamento de Biología Molecular and Centro de Biología Molecular, "Severo Ochoa" (CSIC, Universidad Autónoma de Madrid), Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Truchado-Garcia
authors.affiliation: Department of Metabolic Biochemistry, Ludwig-Maximilians-University, Munich, Germany.|Marine Biological Laboratory, Woods Hole, Massachusetts.
authors.forename: Antje H L
authors.initials: AH
authors.lastname: Fischer
authors.affiliation: Marine Biological Laboratory, Woods Hole, Massachusetts.
authors.forename: Lily W
authors.initials: LW
authors.lastname: Helfrich
authors.affiliation: Marine Biological Laboratory, Woods Hole, Massachusetts.|Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts.
authors.forename: Kimberly B
authors.initials: KB
authors.lastname: Johansson
authors.affiliation: Marine Biological Laboratory, Woods Hole, Massachusetts.
authors.forename: Julie C
authors.initials: JC
authors.lastname: Diamond
authors.affiliation: Departamento de Biología Molecular and Centro de Biología Molecular, "Severo Ochoa" (CSIC, Universidad Autónoma de Madrid), Madrid, Spain.
authors.forename: Cristina
authors.initials: C
authors.lastname: Grande
authors.affiliation: University of Illinois, Department of Cell and Developmental Biology, Urbana, Illinois.
authors.forename: Jonathan Q
authors.initials: JQ
authors.lastname: Henry
mesh_terms: D000818:Animals; D054262:Gastrulation; D015870:Gene Expression; D005809:Genes, Regulator; D005855:Germ Layers / Q000378:metabolism; D038081:Organogenesis; D012908:Snails / Q000196:embryology* / Q000235:genetics / Q000378:metabolism
keywords: EMT; Mollusca; Spiralia; anus; blastopore; endoderm; foregut; gastrulation; hindgut; mesoderm; mouth