Indeed, these vesicles are rich in GPI anchored proteins such as CDw52, CD55, CD59, prion protein, and p25b, and it has been shown that, in vitro, the vesicles can fuse with sperm. Immuno-blotting revealed that several new hydrophobic and lipophilic compounds were bound with the epididymal vesicles. We observed the presence of the very hydrophobic protein 17 kDa secreted by the cauda epididymis and of PGDS secreted in the caput epididymis. One form of E-RABP is also associated with the vesicles, although several different isoforms are secreted in the epididymis.
The 17-kDa protein has been immunolocalized on cauda sperm fla-gellum, but PGDS and E-RABP were not found in the sperm membrane and unpublished results). We have also observed that the main prion protein isoform, a GPI-anchored protein present on epididymal exosomes, was not transferred to the cauda or ejaculated sperm membrane. Exchange of other seminal plasma vesicle membrane-linked proteins have also been described, particularly for dipeptidyl peptidase IV; transfer has been suggested after ejaculation in horse.