Sperm-egg fusion point identified in study

Key molecular events that could be playing a critical role as sperm and egg fuse to create new life have been identified, providing a ray of hope for future male contraceptive, says new study.

"This report expands our fundamental understanding of the molecular architecture at the site of sperm-egg fusion," said John Herr from University of Virginia in the US.

"Understanding at the molecular level exactly how the sperm is able to bind with and enter the egg opens opportunities to identify molecules that can disrupt or block the fertilization event," Herr noted.

When the sperm first arrives at the egg, the sperm contains enzymes to help it penetrate the egg and fuse with its target. The release of these enzymes is known as the acrosomal reaction.

The head of the sperm is completely transformed by this reaction, and tremendous changes begin to take place. But despite this massive remodelling, something intriguing happens, Herr's new research found: A particular protein from within the sperm stays intact at the site of fusion.

This protein remains in place although many other proteins are lost. The evidence indicates that the protein, ESP1, is stabilizing the area where the sperm-egg fusion is occurring.

"We suspect ESP1 is one of the key molecules that helps to stabilize the equatorial segment region of the sperm head," Herr said.

"One of the things that is so interesting about this protein is that as the acrosome forms, the equatorial segment appears to be specified very early in the formation of this organelle," Herr added.

"We don't know enough yet about the protein-protein interactions here to be able to come up with a defined male contraceptive strategy. So it's pretty early in the process of seeing where a small molecule drug might interdict these interactions," Herr added.

The study appeared in the journal Biology of Reproduction.