Objective: To determine whether SED1, a protein secreted by the mouse epididymis that coats sperm and participates in sperm adhesion to the zona pellucida, is present on human sperm and in human epididymal tissue.
Design: SED1 expression was analyzed by immunoblot and indirect immunofluorescence assays.
Setting: Academic clinical and research laboratories.
Patient(s): Human breast milk was donated. Unused semen was donated by men presenting for semen analysis or in vitro fertilization (IVF). Cadaveric epididymal tissue was obtained from the institutional body donor program.
Intervention(s): Human milk fat globule membranes and human seminal plasma proteins were analyzed by immunoblot. Human sperm and epididymis were analyzed by indirect immunofluorescence microscopy. Acrosomal status was determined by staining with fluorescein isothiocyanate-Pisum sativum agglutinin.
Main outcome measure(s): Immunoblot and indirect immunofluorescence assays.
Result(s): Human SED1 is recognized by two different polyclonal anti-SED1 antisera. SED1 is localized to the plasma membrane of human sperm overlying the intact acrosome. In acrosome-reacted sperm, SED1 is localized to the equatorial segment. SED1 is expressed by the epithelium of the anterior caput epididymis.
Conclusion(s): SED1 is expressed on the surface of acrosome-intact human sperm and in the anterior caput of the human epididymis, similar to that seen in mouse.