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Concanavalin A Modifies Allo‐specific Sperm‐Egg Interactions in the Ascidian, Ciona intestinalis

In the self sterile ascidian, Ciona intestinalis, the spermatozoa rarely bind to the vitelline coat of autologous eggs and never penetrate it. We report here that concanavalin A (ConA), a lectin recognizing mannose or glucose residues of carbohydrates, can modify these self‐ and nonself‐specific sperm‐egg interactions. When eggs were pretreated with 0.1–0.5 mg/ml of ConA, about two thousand spermatozoa became attached to the autologous vitelline coat within five minutes of insemination. The effect of ConA was not modified by the addition of D‐mannose or pretreatment of spermatozoa with ConA, showing that ConA does not function merely as a ligand bridging the sperm and vitelline coat. In contrast to the marked enhancement of sperm‐egg binding, ConA did not facilitate the penetration of spermatozoa through the autologous vitelline coat. Even in non‐autologous insemination, it blocked the sperm penetration and, consequently, fertilization did not occur, as shown by Rosati et al. (1978). D‐Mannose, when mixed with ConA in advance, completely abolished this inhibitory effect of ConA. Lotus agglutinin, a fucose‐binding lectin, was less effective and wheat germ agglutinin and soy bean agglutinin had no effect on sperm entry in the perivitelline space. The results of this study are discussed in relation to the possible involvement of mannosyl and/or glucosyl glycoconjugates in allo‐specific sperm‐egg interactions.