Equine sperm-oocyte interaction: the role of sperm surface hyaluronidase.

This research investigates the role of a specific protein known as PH-20 in equine sperm and its contribution to the interaction between the sperm and the egg cell in horses. The study explores the properties of PH-20, the sperm’s reaction to PH-20 and the potential importance of this protein in the process of horse sperm penetrating the layers of the egg cell.

Research Methodology

• The study used sperm samples from five stallions and sperm cells from the epididymis (a part of the male reproductive organ) of 10 stallions.
• A particular component (anti-equine PH-20 polyclonal antibody) was applied to identify the presence and position of PH-20 on the sperm surface.
• The technique of immunolabeling was used to label the entire sperm cell.
• An intracellular calcium indicator, Fluo-3, was used to evaluate intracellular calcium levels in the sperm. Intracellular calcium is the calcium present inside the cells.

Findings

• Stallion sperm was found to express a surface-associated hyaluronidase (a type of enzyme which degrades hyaluronic acid), specifically PH-20, which is situated towards the back of the sperm head. This specific enzyme has been associated with the sperm’s ability to interact with the egg’s outer layer and cumulus cells (cells surrounding the egg).
• Upon undergoing a process known as capacitation (which makes the sperm capable of fertilizing an egg) and exocytosis of a part of the sperm cell known as the acrosome, intense fluorescence of hyaluronidase was observed on an inner membrane of the sperm (inner acrosomal membrane). This suggests that this membrane and hyaluronidase might play an important role in the sperm’s ability to penetrate the egg.
• When sperm were incubated in a medium containing hyaluronan (a component of the egg’s outer layer), an increased level of intracellular calcium concentration was observed. This increase was associated with the relocation of PH-20 antigenic sites on the sperm surface and increase in protein phosphorylation.
• Sperm cells derived from the epididymis showed unique patterns of PH-20 expression, indicating its variable nature during sperm development.

Possible Implications

• The variable expression of PH-20 in ejaculated and epididymal sperm indicates its potential role in aiding the sperm to penetrate cumulus cells, recognizing the egg, and fusing with the outer layer of the egg.