title: Adhesive but not signaling activity of Drosophila N-cadherin is essential for target selection of photoreceptor afferents.
abstract: Drosophila N-cadherin (CadN) is an evolutionarily conserved, atypical classical cadherin, which has a large complex extracellular domain and a catenin-binding cytoplasmic domain. We have previously shown that CadN regulates target selection of R7 photoreceptor axons. To determine the functional domains of CadN, we conducted a structure-function analysis focusing on its in vitro adhesive activity and in vivo function in R7 growth cones. We found that the cytoplasmic domain of CadN is largely dispensable for the targeting of R7 growth cones, and it is not essential for mediating homophilic interaction in cultured cells. Instead, the cytoplasmic domain of CadN is required for maintaining proper growth cone morphology. Domain swapping with the extracellular domain of CadN2, a related but non-adhesive cadherin, revealed that the CadN extracellular domain is required for both adhesive activity and R7 targeting. Using a target-mosaic system, we generated CadN mutant clones in the optic lobe and examined the target-selection of genetically wild-type R7 growth cones to CadN mutant target neurons. We found that CadN, but neither LAR nor Liprin-alpha, is required in the medulla neurons for R7 growth cones to select the correct medulla layer. Together, these data suggest that CadN mediates homophilic adhesive interactions between R7 growth cones and medulla neurons to regulate layer-specific target selection.
authors.affiliation: Unit of Neuronal Connectivity, Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Building 18T, Room 106, MSC 5431, Bethesda, MD 20892, USA.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Yonekura
authors.forename: Lei
authors.initials: L
authors.lastname: Xu
authors.forename: Chun-Yuan
authors.initials: CY
authors.lastname: Ting
authors.forename: Chi-Hon
authors.initials: CH
authors.lastname: Lee
mesh_terms: D000818:Animals; D015820:Cadherins / Q000235:genetics / Q000502:physiology*; D002448:Cell Adhesion / Q000502:physiology; D002478:Cells, Cultured; D004330:Drosophila / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000502:physiology*; D020439:Growth Cones / Q000502:physiology*; D009154:Mutation; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary; D015398:Signal Transduction / Q000502:physiology
chemical_list: D015820:Cadherins; D029721:Drosophila Proteins; D020033:Protein Isoforms