‘Mother’ protein is clincher for making a baby

Scientists observe how human eggs effectively reach out to draw in sperm during fertilisation

‘What we know about fertility in humans has been severely limited by the lack of eggs for research’

FORCED to swim upstream through a barrage of natural barriers, sperm face a friendless battle to beat the competition and fertilise an egg. But now scientists have discovered that at the end of their arduous journey some receive an unexpected helping hand.

A “motherhood” protein on the outside of the egg cell effectively reaches out to grasp the winner and draws it inside the cytoplasm, researchers at the University of Sheffield have found.

It is a part of the fertilisation process that has never been seen before, and scientists believe it could hold the key to why some people struggle to conceive, or why certain sperm are rejected. The protein has been named “Maia” after the Greek goddess of motherhood.

Prof Allan Pacey, co-author of the study and head of the University of Sheffield’s departments of oncology and metabolism and infection, immunity and cardiovascular disease, said: “This discovery of the Maia protein is a major step forward in how we understand the process of human fertilisation.”

Only a few hundred sperm ever come close to an egg, even though men will release between 40 and 150million during ejaculation.

Although the uterus helps the sperm move towards the fallopian tube that holds the egg, the female body throws up a host of immune obstacles along the way, which only the strongest and healthiest swimmers can overcome.

Even when sperm does reach its destination, they can still struggle to trigger fertilisations, for reasons that scientists do not fully understand.

To learn more about which proteins were helping or hindering the process, scientists created thousands of artificial eggs from beads, and attached different pieces of protein – known as peptides – on their surface to see if any triggered bonding. After introducing sperm to the fake eggs and incubating them together, researchers found that only those with parts of the Maia protein successfully connected.

To check that the protein was definitely responsible, the team then inserted the gene that makes Maia into human culture cells, and found they became receptive to sperm in the same way as eggs.

Prof Harry Moore, lead investigator of the study from the University of Sheffield’s school of biosciences, said: “The ingenious artificial fertilisation technique, which enabled us to identify the Maia protein, will not only allow scientists to better understand the mechanisms of human fertility, but will pave the way for novel ways to treat infertility and revolutionise the design of future contraceptives.

“Infertility is unexplained in more than half of those who struggle to conceive naturally. What we know about fertility in humans has been severely limited by ethical concerns and the lack of eggs for research,” he added.

Scientists now want to explore whether sperm from different individuals bind to the Maia protein differently. They are hoping the findings may help to confirm the theory that some sperm may not be compatible with some eggs, which could explain many cases of infertility.

Prof Pacey added: “It would have been almost impossible to discover without the use of the artificial beads … as we simply wouldn’t have been able to get enough eggs to do the experiment.

“A classic case of thinking out of the box,” he said.

The findings are published in the journal Science Advances.