Identification of four classes of cell surface antigens appearing at gastrulation in sea urchin embryos

An antiserum to isolated membranes of gastrula-stage embryos of the sea urchin Lytechinus variegatus was characterized by absorption and cell agglutination specificities. The antiserum was found to recognize four distinct classes of antigens on the embryonic cell surface: (1) an early embryonic class or “maternal” class present from the earliest stages of development, (2) an embryonic class of antigens which appeared on all cells beginning at gastrulation, (3) a class of antigens present on ectoderm cells, and (4) a class of antigens present on endoderm cells. All four classes of antigens were shown indirectly to be synthesized on embryonic mRNA since a hybrid embryo of the cross Tripneustes ♀ × Lytechinus ♂ expressed all four classes of Lytechinus-specific antigens beginning at gastrulation. Each class was Lytechinus specific in that hybrid cells were agglutinated if beyond the beginning of gastrulation, while normal Tripneustes ♀ × Tripneustes ♂ cells were not agglutinated.