title: Quantitative analysis of epithelial cell aggregation in the simple metazoan Hydra reveals a switch from homotypic to heterotypic cell interactions.
abstract: Hydra, a member of the diploblastic phylum Cnidaria, exhibits the most basic type of organized metazoan tissues. Two unicellular sheets of polarized epithelial cells - ectoderm and endoderm - form a double layer throughout the body column. The double layer can be reestablished from single-cell suspensions by tissue-specific cell-sorting processes. However, the underlying pattern of interactions between ectodermal and endodermal epithelial cells responsible for double-layer formation is unclear. By analyzing cell interactions in a quantitative adhesion assay using mechanically dissociated Hydra epithelial cells, we show that aggregation proceeds in two steps. First, homotypic interactions within ectodermal epithelial cells (ecto-ecto) and within endodermal epithelial cells (endo-endo) form homotypic cell clusters. Second, at an aggregate size of about ten epithelial cells/cluster, ectodermal and endodermal clusters start to form heterotypic aggregates. Homotypic ecto-ecto interactions are inhibited by a polyclonal anti-Hydra membrane antiserum, and under these conditions homotypic endo-endo interactions do not proceed beyond a size of about ten epithelial cells/cluster. These data suggest that homotypic cell clusters reduce their initial homotypic affinity and acquire a new heterotypic affinity. A link between cell adhesion and cell signaling in early Hydra aggregates is discussed.
authors.affiliation: Department of Molecular Cell Biology, University of Technology, Darmstadt, Germany. hobmayer@bio.tu-darmstadt.de
authors.forename: B
authors.initials: B
authors.lastname: Hobmayer
authors.forename: P
authors.initials: P
authors.lastname: Snyder
authors.forename: D
authors.initials: D
authors.lastname: Alt
authors.forename: C M
authors.initials: CM
authors.lastname: Happel
authors.forename: T W
authors.initials: TW
authors.lastname: Holstein
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002118:Calcium / Q000502:physiology*; D002448:Cell Adhesion / Q000502:physiology; D002449:Cell Aggregation / Q000502:physiology*; D002450:Cell Communication / Q000502:physiology*; D002452:Cell Count; D002465:Cell Movement / Q000502:physiology; D002469:Cell Separation / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004475:Ectoderm / Q000166:cytology / Q000502:physiology; D004707:Endoderm / Q000166:cytology / Q000502:physiology; D004847:Epithelial Cells / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D019084:Fluorescent Antibody Technique, Indirect; D006829:Hydra; D009154:Mutation; D012680:Sensitivity and Specificity; D014018:Tissue Distribution / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D002118:Calcium