title: Scaling of the BMP activation gradient in Xenopus embryos.
abstract: In groundbreaking experiments, Hans Spemann demonstrated that the dorsal part of the amphibian embryo can generate a well-proportioned tadpole, and that a small group of dorsal cells, the 'organizer', can induce a complete and well-proportioned twinned axis when transplanted into a host embryo. Key to organizer function is the localized secretion of inhibitors of bone morphogenetic protein (BMP), which defines a graded BMP activation profile. Although the central proteins involved in shaping this gradient are well characterized, their integrated function, and in particular how pattern scales with size, is not understood. Here we present evidence that in Xenopus, the BMP activity gradient is defined by a 'shuttling-based' mechanism, whereby the BMP ligands are translocated ventrally through their association with the BMP inhibitor Chordin. This shuttling, with feedback repression of the BMP ligand Admp, offers a quantitative explanation to Spemann's observations, and accounts naturally for the scaling of embryo pattern with its size.
authors.affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Danny
authors.initials: D
authors.lastname: Ben-Zvi
authors.forename: Ben-Zion
authors.initials: BZ
authors.lastname: Shilo
authors.forename: Abraham
authors.initials: A
authors.lastname: Fainsod
authors.forename: Naama
authors.initials: N
authors.lastname: Barkai
mesh_terms: D000818:Animals; D019521:Body Patterning; D049628:Body Size; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000196:embryology / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008024:Ligands; D008954:Models, Biological; D021381:Protein Transport; D014981:Xenopus / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029867:Xenopus Proteins / Q000378:metabolism
chemical_list: D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D008024:Ligands; D029867:Xenopus Proteins; C499591:admp protein, Xenopus; C525812:bmp4 protein, Xenopus; C054234:chordin