Progesterone-induced acrosome reaction in stallion spermatozoa is mediated by a plasma membrane progesterone receptor.

This study examines how progesterone triggers the acrosome reaction (AR) in stallion sperm cells, suggesting that this process is facilitated by a progesterone receptor on the sperm’s plasma membrane.

Research Objectives

• The main objective of this research was to uncover whether progesterone’s ability to induce AR in stallion sperm cells was facilitated by a receptor on the exterior plasma membrane, or through an internal progesterone receptor.

Methodology

• The researchers used a fluorescently labeled progesterone-BSA (Bovine Serum Albumin) conjugate (P-BSA-FITC) combined with a vitality stain, ethidium homodimer, to visualize the presence of the progesterone receptor while the sperm were still alive.
• An indirect immunofluorescence technique using the C-262 monoclonal antibody, designed to bind to human intracellular progesterone receptor, was used to confirm the presence of the progesterone receptor.
• They also utilized immunogold labelling techniques, combined with transmission electron microscopy, to locate the P-BSA-FITC or C-262 at an ultrastructural level.
• During a five-hour capacitation period, the labels’ dynamic changes were continuously monitored using fluorescence microscopy and flow cytometry.

Results and Conclusions

• Observations revealed an increasing number of viable sperm cells that showed an affinity for P-BSA-FITC or C-262 at the acrosomal plasma membrane region of the sperm head, suggesting the presence of a progesterone receptor at this location.
• In contrast, almost all deteriorated cells were labeled in the cytosol of the postequatorial region of the sperm head.
• Incubation with P-BSA-FITC initiated AR, though to a lesser extent than that observed for sperm incubated with free progesterone.
• These findings suggest that the progesterone’s binding to a receptor on the sperm plasma membrane is critical in triggering AR in stallion spermatozoa.