title: The modulation of cell adhesion molecule expression and intercellular junction formation in the developing avian inner ear.
abstract: The cells that constitute the membranous labyrinth in the vertebrate inner ear are all derived from a single embryonic source, namely, the otocyst. The mature inner ear epithelia contain different regions with highly differentiated cells, displaying a highly specialized cytoarchitecture. The present study was designed to determine the presence of adherens-type intercellular junctions in this tissue and study the expression of cell adhesion molecules (CAMs) associated with these junctions, namely, A-CAM and L-CAM, in the developing avian inner ear epithelia. The results presented here show that throughout the early otocyst, A-CAM is coexpressed with L-CAM. The formation of asymmetries between sensory and nonsensory areas in the epithelium is accompanied by the modulation of CAMs expression and the assembly of intercellular junctional complexes. A-CAM and L-CAM display reciprocal expression patterns, the former being expressed mostly in the mosaic sensory epithelium, while L-CAM becomes conspicuous in the nonsensory areas but its expression in the sensory region is markedly reduced. Adherens-type junctions and numerous desmosomes are found in the junctional complexes of early otocyst cells. The former persist to maturity of the various inner ear epithelia, whereas desmosomes disappear from junctional complexes of hair cells but remain in the intercellular junctional complexes of all other cell types in the membranous labyrinth. Thus, adherens type intercellular junctions comprise the only defined cytoskeleton-bound junction in mature hair cells. A-CAM-positive cells are also found in the region of the acoustic ganglion in early developmental stages but not in the mature neural elements.
authors.affiliation: Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Y
authors.initials: Y
authors.lastname: Raphael
authors.forename: T
authors.initials: T
authors.lastname: Volk
authors.forename: K L
authors.initials: KL
authors.lastname: Crossin
authors.forename: G M
authors.initials: GM
authors.lastname: Edelman
authors.forename: B
authors.initials: B
authors.lastname: Geiger
mesh_terms: D000199:Actins / Q000235:genetics; D000818:Animals; D000954:Antigens, Surface / Q000235:genetics*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D002454:Cell Differentiation; D002642:Chick Embryo; D002645:Chickens; D003896:Desmosomes / Q000648:ultrastructure; D007758:Ear, Inner / Q000196:embryology* / Q000378:metabolism / Q000648:ultrastructure; D004848:Epithelium / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D006651:Histocytochemistry; D007365:Intercellular Junctions / Q000648:ultrastructure*; D008562:Membrane Glycoproteins; D008854:Microscopy, Electron; D009024:Morphogenesis; D013997:Time Factors
chemical_list: D000199:Actins; D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D008562:Membrane Glycoproteins