August 19, 2011

Scientists Determine How An Egg Captures Sperm

Scientists have discovered exactly how a human egg captures incoming sperm to begin the process of fertilization.

The new study could help future couples who suffer from infertility.

The international team of researchers found that a specific kind of sugar molecule makes the outer coat of the egg "sticky," which helps the egg and sperm bind together.

"The details we've discovered here fill in a huge gap in our knowledge of fertility and we hope they will ultimately help many of those people who currently cannot conceive," Anne Dell of Imperial College London, who worked on the study with scientists from the universities of Missouri and Hong Kong, and the Academia Sinica in Taiwan, said in a press release.

The World Health Organization said that infertility affects up to 15 percent of reproductive-aged couples around the world and almost one in every seven couples in Britain has problems conceiving a child.

Scientists are already aware that sperm "recognizes" an egg when proteins on the head of the sperm meet and match a series of specific sugars in the egg's outer coating. Â

Once a successful match has ben made, the outside surfaces of the sperm and egg bind together before they merge and the sperm delivers the DNA to its inside, fertilizing the egg.

Researchers in this new study used ultra-sensitive mass-spectrometric imaging technology to assess which molecules were most likely to be key in the binding process.

After experimenting with a range of synthesized sugars in the lab, the team found that a sugar chain known as the sialyl-lewis-x sequence is abundant on the surface of the human egg.

The researchers then tested their findings using the outer coats of unfertilized "non-living" human eggs.

Dell said the study was difficult "because human eggs are very tiny -- about the size of a full stop -- so we didn't have much material to work with."

Poh-Choo Pang, who also worked on the study, said that although clinical treatments derived from this discovery are a long way off, it could open up new possibilities for understanding fertility problems faced by many couples.

The researchers said they want to use the findings of this work to further investigate the proteins on the head of a sperm that enable it to recognize an egg.

The study was published in the journal Science.


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