Secreted Epididymal Glycoprotein: INTRODUCTION(1)
Mammalian spermatozoa acquire their motility and fertilizing capacity during passage through the epididymal duct. Concomitant with these changes in functionality, there is reorganization of the nucleoprotein; alterations in the structure and composition of the acrosome, mitochondria, and flagellum; and remodeling of the plasma membrane. The changes to the plasma membrane are of special significance, as it is primarily this organelle that regulates cross talk with surrounding fluids and responds to signals from the egg at fertilization. add comment
The changes in the antigenic profile of the sperm plasma membrane during maturation in the epididymis are due largely to exchange of glycoproteins with the luminal fluid accompanied by processing of existing antigens with or without their repositioning to different regions of the cell surface. Although many epididymal glycoproteins have now been characterized and their interaction with the sperm plasma membrane well documented, several problems remain. First, the mechanism of secretion (exocrine versus apocrine) of glycoproteins by epididymal principal cells is still contentious. It is not clear if they are present in a fully soluble form or, as has been suggested, are attached to membrane-bound vesicles known as epididymosomes (cf. prostasomes from the prostate) and are then transferred by unknown mechanisms to the sperm’s plasma membrane.