Key to sperm-to-egg binding found
7 Jun 2012 by Evoluted New Media
Key to fertility in mammals is a gene and its encoded protein – protein disulphide isomerase homolog (PDILT) – which enables sperm to bind to an egg say researchers in the UK and Japan.
Scientists from Durham and Osaka Universities switched off the gene in male mice and tracked the ability of sperm to bind to and fertilise eggs in both Petri dishes and mice – less than 3% of eggs were fertilised compared to more than 80% when the gene was left switched on.
Sperm from mice with the gene switched off will not bind to a bare egg, but will bind to an egg surrounded by cumulous cells. These cells protect the egg and play an important role in fertility by enabling sperm to bind properly to an egg.
“The protein is an essential part of the navigation system of sperm,” said Dr Adam Benham from the School of Biological and Biomedical Sciences at Durham. “It helps sperm swim through the oviduct to the egg and without it sperm get stuck. Our results show that navigating the oviduct is an important part of the fertilisation process.
“Like any navigation system, you have to programme where it is that you want to go and this protein plays an essential role in getting sperm to the right destination, in good shape and in good time.”
Researchers discovered PDILT helps another gene product called ADAM3 – a disintegration and metalloproteinase 3 – which is critical for sperm migration from the uterus into the oviduct and for sperm primary binding.
The findings show the importance of PDILT in the process of sperm-to-egg-binding and enabling the sperm to navigate its way to the egg.
“We now hope to discover how the PDILT protein affects fertility in humans,” said Benham. “Mutations in the gene may be responsible for unexplained male fertility problems and further research may aid more effective IVF treatment.”
The researchers – who published their findings in Proceedings of the National Academy of Sciences – now hope to look at how the gene affects sperm-to-egg binding in humans.
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