Concanavalin A‐Induced Morphological Changes and Its Binding Sites in Starfish Follicle Cells as Revealed by Electron Microscopy

Abstract

Concanavalin A (Con A) stimulates the production in starfish follicle cells of 1‐methyladenine, a hormone which induces oocyte maturation. We have therefore investigated Con A‐induced morphological changes and Con A‐binding sites in the follicle cell using native Con A and horseradish peroxidase‐ or ferritin‐labeled Con A (HRP‐Con A, Fer‐Con A). After isolated follicle cells were incubated with Con A (1 mg/ml), vacuoles, the Golgi complex and multivesicular body‐like organelles (MVBs) became prominent in most of the cells. After follicle cells were prefixed and then incubated with Fer‐Con A for 60 min, tagged ferritin was diffusely and randomly distributed as single or small clustered particles on the cell surface. The incubation of isolated follicle cells with Fer‐Con A for 10 min before fixation resulted in numerous ferritin particles localized along the internalized membrane, and also in vacuoles, MVBs and small lysosome‐like structures. After 60 min incubation with Fer‐Con A, ferritin was further located in large lysosome‐like structures and in vesicles near and in the Golgi area as well as in the organelles described above. HRP‐Con A binding sites were also observed in vacuoles and MVBs of the intact cells. These results suggest that Con A binds at first to the cell surface and causes rapid internalization and that membrane‐bound Con A is easily endocytosed into vacuoles, MVBs and lysosome‐like structures, and is later incorporated in some vesicles in the Golgi area.