title: The roles of an ephrin and a semaphorin in patterning cell-cell contacts in C. elegans sensory organ development.
abstract: Ephrins and semaphorins regulate a wide variety of developmental processes, including axon guidance and cell migration. We have studied the roles of the ephrin EFN-4 and the semaphorin MAB-20 in patterning cell-cell contacts among the cells that give rise to the ray sensory organs of Caenorhabditis elegans. In wild-type, contacts at adherens junctions form only between cells belonging to the same ray. In efn-4 and mab-20 mutants, ectopic contacts form between cells belonging to different rays. Ectopic contacts also occur in mutants in regulatory genes that specify ray morphological identity. We used efn-4 and mab-20 reporters to investigate whether these ray identity genes function through activating expression of efn-4 or mab-20 in ray cells. mab-20 reporter expression in ray cells was unaffected by mutants in the Pax6 homolog mab-18 and the Hox genes egl-5 and mab-5, suggesting that these genes do not regulate mab-20 expression. We find that mab-18 is necessary for activating efn-4 reporter expression, but this activity alone is not sufficient to account for mab-18 function in controlling cell-cell contact formation. In egl-5 mutants, efn-4 reporter expression in certain ray cells was increased, inconsistent with a simple repulsion model for efn-4 action. The evidence indicates that ray identity genes primarily regulate ray morphogenesis by pathways other than through regulation of expression of semaphorin and ephrin.
authors.affiliation: Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Hahn
authors.forename: Scott W
authors.initials: SW
authors.lastname: Emmons
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D036342:Ephrins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D007365:Intercellular Junctions / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; C470369:EFN-4 protein, C elegans; D036342:Ephrins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C405025:mab-20 protein, C elegans