The presence of Müllerian inhibiting substance binding sites in human sperm

The binding of Müllerian inhibiting substance (MIS) to human sperm was investigated using immunohistological techniques.

Sperm from 5 normal donors and 6 subfertile men were studied. Whole or thin-sectioned sperm were incubated without or with recombinant human MIS (0.5 microg./ml.). MIS binding was identified under light microscopy (LM) using rabbit anti-human MIS antibodies tagged with goat IgG-horseradish peroxidase and diaminobenzidine as substrate, or by scanning and transmission electron microscopy (SEM and TEM) using gold labeled goat IgG. Intracellular MIS binding in sperm sections was examined by TEM. Antibodies were omitted in the controls.

Under LM, DAB staining was present on sperm incubated with or without MIS and absent on controls. Using SEM, gold particles were found primarily on the surfaces of the sperm head with less binding to the tail. With TEM, the clustering of gold particles around the head of sperm represents MIS binding, but very few or no gold particles could be found associated with the sperm tail. MIS binding was also found associated with intracellular structures, but only within the head of the sperm. Overall, less gold particle binding was present in subfertile compared with normal sperm.

These results suggest that MIS is bound to the sperm surface and sperm from normally fertile men have increased MIS binding. The function of MIS in sperm is unknown, but the presence of MIS binding suggests a direct role(s) in sperm function.