Hamster sperm antigen P26h is a phosphatidylinositol-anchored protein

have previously identified a hamster sperm protein, P26h, proposed to be in volved in the interaction between spermatozoa and the egg's zona pellucida. In this study we investigated the mechanism of P26h accumulation on hamste r spermatozoa during epididymal maturation. Immunocytochemical studies show ed an accumulation of P26h on the acrosomal cap of hamster spermatozoa duri ng epididymal transit. To document the anchoring mechanism of P26h, cauda e pididymal spermatozoa were exposed to different treatments. High-salt buffe red solutions were unable to remove P26h from the surface of intact spermat ozoa. P26h was released in a dose-dependent manner when live spermatozoa we re treated with a solution of phospholipase C specific to phosphatidylinosi tol. in contrast, the P26h remained associated to the sperm surface followi ng treatment with trypsin. To document the transfer mechanisms of P26h on t he maturing spermatozoa, prostasomes were isolated from the epididymal flui d and subjected to immunodetection. Western blots and immunogold studies sh owed that P26h was associated to epididymal prostasomes. Phospholipase C tr eatment performed on epididymal prostasomes, indicated that P26h also is an chored to these vesicles via a phosphatidylinositol. These results suggest that epididymal sperm maturation involves a cell to cell transfer of a phos phaditylinositol-anchored protein and that prostasomes may be implicated in this process. Mol. Reprod. Dev. 52:225-233, 1999. (C) 1999 Wiley-Liss, Inc .