Protein that helps sperm fuse with egg identified

A newly discovered protein which facilitates egg and sperm fusion provides new insights into human fertilisation.

Over half of infertility cases cannot be explained, meaning that treatments based on current understanding may not be effective for every patient. Using an artificial fertilisation technique, researchers have revealed a novel protein controlling the attachment of sperm to eggs, shedding new light on the mechanisms of conception.

Professor Harry Moore of the University of Sheffield and lead author of the study said: '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.'

The study, published in Science Advances, describes how the team used microscopic beads, each coated with a specific protein fragment, to screen the role of many proteins in sperm-to-egg attachment. Using this method, they discovered that beads coated with a section of one protein, MAIA, named after the Greek goddess of motherhood, bound a high number of sperm.

The scientists showed that MAIA acts together with a previously identified sperm-binding protein called JUNO to anchor sperm to the egg's surface (see BioNews 751). They introduced the genes for MAIA and JUNO into hamster egg cells and found that this enabled them to bind human sperm, something they ordinarily would not be able to do.

PET trustee, Professor Allan Pacey of the University of Sheffield and co-author of the study said: 'This discovery of the MAIA protein is a major step forward in how we understand the process of human fertilisation. It would have been almost impossible to discover without the use of the artificial beads to replicate the surface of human eggs 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.'

These findings elucidate how gamete fusion occurs and could explain the idea that, between humans, some people's sperm may not be compatible with others' eggs. The discovery of this mechanism and future work could help explain why some patients cannot easily conceive.

Professor Moore commented: '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.'