Research using mice has revealed a new gene that plays an essential role in mammalian fertility: the PDILT gene encodes a protein that enables sperm to navigate their way through the oviduct and bind correctly to the egg during the process of fertilisation. The PDILT protein stimulates the correct folding of another protein called ADAM3, which is then localised to the outer membrane of the sperm. Without PDILT, the ADAM3 protein is not folded correctly or transported to where it is needed to be. Its critical importance was evident following the discovery that if its expression is ‘switched off’ in sperm, fewer than 3% of eggs become fertilised, in comparison with approximately 80% when the gene is active. Sperm lacking PDILT are not only unable to bind the egg fully, but find it difficult to navigate through the oviduct to get to it in the first place. The experiments also revealed that what are known as cumulus cells, which form a protective layer around the egg, aid in effective binding of the sperm to the egg and will help to rescue the binding difficulties caused by the absence of PDILT, enabling successful fertilisation. The next step will be to examine how the gene works in humans - from there, it may be possible to produce fertility treatments that could aid in making IVF more successful for those couples that are faced with low fertility.
Ref: Durham University, 2012. Gene involved in sperm-to-egg binding is key to fertility in mammals. EurekAlert! News [link]