Micromere-specific cell surface proteins of 16-cell stage sea urchin embryos

Evidence is presented of cell-type specificity of surface proteins from the 16-cell stage sea urchin embryo. The protein composition of the micromere cell surface has been examined by 125I labelling of intact cells followed by SDS-PAGE. In Arbacia punctulata, four high molecular weight (HMW) proteins are detected on the surface of isolated micromeres--but not on mesomere-macromere fractions. In Strongylocentrotus droebachiensis, a micromere-specific protein of 133 K molecular weight (MW) was identified. This 133 K protein binds to wheat germ agglutinin (WGA) but not to concanavalin A (conA). Lectin binding was studied using a new technique. The procedure involves the separation, by SDS-PAGE, of iodinated cell-surface proteins followed by their electrophoretic transfer to lectin-coated nitrocellulose membranes. Using this procedure, cell-type-specific surface proteins which are also lectin-binding-specific, were detected.