New Insight into Male Infertility

Researchers have identified a new protein that is required for a sperm to bind to an egg during the process of fertilization, suggesting the cause for some instances of male infertility. The finding was reported in the August 22, 2003, issue of Cell.

In many cases the sperm of infertile men appear to be completely normal. The researchers focused on the specific molecules and events required for a sperm to recognize an egg so that fertilization can take place. They identified a protein on the surface of mouse sperm that is required for the sperm to successfully bind to the outside of the egg. This protein, called SED1, binds specifically to unfertilized eggs, and no longer recognizes an egg after it has been fertilized. In the laboratory, sperm without SED1 were unable to bind to an egg, and mice without SED1 had greatly reduced fertility even though their sperm were normal in number and motility.

"An understanding of the molecular mechanisms underlying sperm-egg binding may give insight into the basis for at least some percentage of male infertility,” explained Barry D. Shur, Ph.D., professor and chair of cell biology at Emory University School of Medicine (Atlanta, GA, USA; www.emory.edu). "In addition, this work is of interest because the composition of SED1 is similar to other types of cell-cell binding proteins, which have not previously been implicated in sperm-egg binding.”




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