Rapid identification of lectin receptors and their possible function in sea urchin cell systems

An assay using lectin derivatized agarose beads to rapidly and inexpensively identify cell surface lectin receptors was recently described by Latham et al. (1995). In this earlier study, the assay was tested on large, early stage sea urchin embryo cells. In this study this assay was used to examine lectin receptors on small, later stage sea urchin embryo cells that are more typical of cells that most investigators deal with, to ascertain if cell size is a determining factor in the assay's validity. The results indicated that the assay is a valid method to identify lectin receptors on small as well as large cells. Twenty-three hour Strongylocentrotus purpuratus embryo cells strongly bound Triticum vulgaris, concanavalin A, Artocarpus integrifolia and Vicia villosa using both the agarose bead and fluorescence assays, while three other lectins, Ulex europaeus I, Lotus tetragonolobus and Lens culinaris did not strongly bind to the cells using these two assays. As in earlier studies agglutinability results did not correlate well with results using the two other assays. In all cases where lectin bead binding, fluorescent lectin binding or lectin-mediated agglutination occurred, specific sugars reduced the observed binding. The second part of this study examined the putative role of concanavilin A receptors in a specific cellular interaction: sperm-egg binding. Concanavalin A inhibited fertilization of dejellied sea urchin eggs when their vitelline layers were intact and to a lesser extent when their vitelline layers were removed. This effect was counteracted by alpha methyl glucose. The major differences between these studies and previous work is that here concanavalin A was washed out after incubation with eggs, making it more likely that results reflect binding to cell surface lectin receptors rather than toxicity. In addition, performing the experiments on eggs with or without vitelline layers provided information on the location of concanavalin A receptors that may function in sperm-egg interaction.