title: Ultrastructural localization of lectin-binding sites on the zonae pellucidae and plasma membranes of mammalian eggs.
abstract: Receptors for Ricinus communis agglutinin I (RCAI), concanavalin A (Con A), and wheat germ agglutinin (WGA) were localized on the zonae pellucidae and plasma membranes of hamster, mouse, and rat eggs with ferritin-lectin conjugates. Intact eggs labeled with the ferritin conjugates showed dense concentrations of RCAI and WGA receptors in the outermost regions of their zonae pellucidae and sparse distributions of Con A receptors throughout the zonae. Ferritin-lectin labeling was specific, since inhibitory saccharides effectively blocked labeling. The asymmetric density of RCAI receptors across the zona was confirmed by ferritin-RCAI and fluorescein-RCAI labeling of mechanically isolated zonae pellucidae, indicating that the RCAI-binding sites are more densely distributed in the exterior zona regions. Plasma membranes of rodent eggs contained RCAI, WGA, and Con A receptors. These receptors were found to be more or less randomly distributed on surfaces of aldehyde-fixed eggs or on eggs labeled near 0 degrees C. However, eggs incubated at 25 degrees C showed aggregated WGA- and Con A-binding site distributions on their plasma membranes. This indicates that lectin-induced receptor redistribution occurs at this temperature. The possibility that plasma membrane receptor mobility is a requirement for sperm-egg fusion is discussed.
mesh_terms: D000818:Animals; D001666:Binding Sites, Antibody; D002462:Cell Membrane / Q000276:immunology / Q000648:ultrastructure; D003208:Concanavalin A / Q000378:metabolism; D006224:Cricetinae; D005260:Female; D005293:Ferritins; D005452:Fluoresceins; D037102:Lectins; D051379:Mice; D008854:Microscopy, Electron; D008858:Microscopy, Phase-Contrast; D010063:Ovum / Q000276:immunology / Q000648:ultrastructure*; D037121:Plant Lectins; D010947:Plants, Toxic; D051381:Rats; D012278:Ricinus; D013696:Temperature; D014908:Triticum; D015044:Zona Pellucida / Q000276:immunology / Q000648:ultrastructure*
chemical_list: D005452:Fluoresceins; D037102:Lectins; D037121:Plant Lectins; D003208:Concanavalin A; D005293:Ferritins