Local variation of the cell surface in chum salmon sperm as revealed by their agglutination reaction

The sperm of the chum salmon, Oncorhynchus keta , possesses a bilaterally symmetrical organization by virtue of lateral extensions of the tail flagellum. An active movement of these sperm was induced immediately after incubation in well water but ceased within 2 min. A marked swelling of the cell body with coiling of the axoneme was observed during the incubation. Concanavalin A (Con A), Ricinus communis agglutinin (RCA 60 ), and egg agglutinin from chum salmon eggs were able to induce sperm agglutination; reticular aggregates of the sperm were formed by the activity of egg agglutinin, whereas irregularly shaped clumps were produced by Con A and RCA 60 . Soybean agglutinin, Ulex europeus agglutinin, and wheat germ agglutinin were unable to induce sperm agglutination. Electron microscopy revealed that the aggregate or clump formations brought about by egg agglutinin and lectins are largely due to the elongation and entanglement of lateral extensions of different sperm flagella; no head‐to‐head attachment was observed. Although the aggregate formation by egg agglutinin was not inhibited by any of the sugar inhibitors used, sperm agglutination by Con A or RCA 60 was blocked either by α‐methyl‐D‐mannoside or N‐acetyl‐D‐galactosamine. Con A binding sites of the cell surface detected by means of fluorescein isothiocyanate‐ or ferritin‐conjugated Con A were found to be restricted to the sperm tail, mostly to the surface of its lateral extensions. Polyethylene glycol also induced the elongation of lateral extensions of the tail flagellum; the actual fusion between different sperm occurred at the tips of these elongated extensions. No head‐to‐head or head‐to‐tail fusion was observed. We conclude that a local variation in the physiological property of the cell surface existing in the chum salmon sperm is correlated with the differential distribution of carbohydrate residues in the plasma membrane. These results in relation to early events in the fertilization of teleost eggs are discussed.