It takes a sticky egg to catch sperm

Kathleen Blanchard's picture
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Researchers have finally discovered how a human egg binds to sperm to create new life. University of Missouri, the University of Hong Kong, Academia Sinica in Taiwan and Imperial College London scientists have identified a sugary substance that coats human eggs, which is essential for catching sperm for reproduction.

SLeX coats human eggs

With the help of technology known as mass spectrometry, the scientists found a sugar chain known as the sialyl-lewis-x sequence (SLeX) is present on the coating of eggs.

Professor Anne Dell CBE FRS FMedSci from the Department of Life Sciences at Imperial College London led the research and made the discovery that has taken researchers thirty years to uncover.

Dell explained, “This endeavour was an enormously difficult task because human eggs are very tiny - about the size of a full stop - so we didn't have much material to work with." She adds, “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."

The World Health Organization (WHO) reports 15 percent of couples are unable to conceive.

Side effects of fertility treatment for women include risk of multiple pregnancy, bleeding and infection with assisted fertility treatments and low birth weight, according to Mayoclinic.com.

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How SLeX works

In the study, researchers discovered the sugars on the outside of the egg are recognized by proteins on the head of sperm.

The scientists tested how SLeX in-vitro.

In the lab, the scientists bisected the tiny eggs, and then coated one half with a chemical to disguise SLeX. The untreated half attracted sperm, but the half of the egg that was coated was ignored.

William Yeung from the Department of Obstetrics and Gyneacology and the Centre for Reproduction, Development and Growth at the University of Hong Kong, said there is still more to be learned about exactly how sperm recognizes the sticky egg coating to penetrate and deposit DNA.

Now that scientists have discovered the sugary coating SLeX is what catches sperm to create life, they want to know how proteins on sperm recognize human eggs. The authors say the discovery won’t lead to fertility treatments anytime soon, but the finding opens doors for new options that might help couples conceive.

Science DOI: 10.1126/science.1207438
"Human Sperm Binding Is Mediated by the Sialyl-Lewisx Oligosaccharide on the Zona Pellucida"
Poh Choo Pang, et al., August 18, 2011

Image credit: Wikimedia commons

Updated 8/31/2014

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