title: Variable combinations of specific ephrin ligand/Eph receptor pairs control embryonic tissue separation.
abstract: Ephrins and Eph receptors are involved in the establishment of vertebrate tissue boundaries. The complexity of the system is puzzling, however in many instances, tissues express multiple ephrins and Ephs on both sides of the boundary, a situation that should in principle cause repulsion between cells within each tissue. Although co-expression of ephrins and Eph receptors is widespread in embryonic tissues, neurons, and cancer cells, it is still unresolved how the respective signals are integrated into a coherent output. We present a simple explanation for the confinement of repulsion to the tissue interface: Using the dorsal ectoderm-mesoderm boundary of the Xenopus embryo as a model, we identify selective functional interactions between ephrin-Eph pairs that are expressed in partial complementary patterns. The combined repulsive signals add up to be strongest across the boundary, where they reach sufficient intensity to trigger cell detachments. The process can be largely explained using a simple model based exclusively on relative ephrin and Eph concentrations and binding affinities. We generalize these findings for the ventral ectoderm-mesoderm boundary and the notochord boundary, both of which appear to function on the same principles. These results provide a paradigm for how developmental systems may integrate multiple cues to generate discrete local outcomes.
authors.affiliation: Department of Biology, McGill University, Montreal, Quebec, Canada.
authors.forename: Nazanin
authors.initials: N
authors.lastname: Rohani
authors.affiliation: Complex Systems and Non Linear Phenomena, L2C-UMR 5221 CNRS-UM2, Montpellier, France; Biological Physics and Systems Biology, DIMNP-UMR 5235 CNRS-UM2 et 1, Montpellier, France.
authors.forename: Andrea
authors.initials: A
authors.lastname: Parmeggiani
authors.affiliation: Department of Cell and Systems Biology, University of Toronto, Toronto, Canada.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Winklbauer
authors.affiliation: Department of Biology, McGill University, Montreal, Quebec, Canada.
authors.forename: François
authors.initials: F
authors.lastname: Fagotto
mesh_terms: D000818:Animals; D004475:Ectoderm / Q000254:growth & development / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D036387:Ephrin-B1 / Q000235:genetics / Q000378:metabolism; D036388:Ephrin-B2 / Q000235:genetics / Q000378:metabolism; D036389:Ephrin-B3 / Q000235:genetics / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D008648:Mesoderm / Q000254:growth & development / Q000378:metabolism*; D051379:Mice; D009024:Morphogenesis / Q000235:genetics*; D009672:Notochord / Q000254:growth & development / Q000378:metabolism*; D036122:Receptor, EphA4 / Q000235:genetics / Q000378:metabolism; D036183:Receptor, EphB2 / Q000235:genetics / Q000378:metabolism; D036224:Receptor, EphB4 / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014982:Xenopus laevis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism
chemical_list: D036387:Ephrin-B1; D036388:Ephrin-B2; D036389:Ephrin-B3; D011994:Recombinant Proteins; D036122:Receptor, EphA4; D036183:Receptor, EphB2; D036224:Receptor, EphB4