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Posts Tagged ‘sperm-egg binding’


 

Reporter and Curator: Dr. Sudipta Saha, Ph.D.

 

An estimated 10 to 15% of couples suffer from infertility, and many treatment decisions rely on trial and error. A team of international scientists has found a common genetic variant which may explain why some men with normal sperm counts and good quality sperm are affected by infertility.

The study findings suggested that men with a variation in a gene which codes for a sperm-coating protein called beta defensin 126 (DEFB126) have a reduction in the protein coat on the outside of the sperm which makes it difficult for the sperm to ‘swim’ to the egg.

Dr Edward Hollox of the University of Leicester and co-author of the study said: ‘If you’ve got this gene variant you should allow that little bit longer if your partner’s planning to get pregnant’. The researchers, including scientists from the University of California and the Anhui Medical University in China, carried out the study on over 500 newly-wed Chinese couples who were trying for a baby.

They found that when men’s sperm lacked a coat of the DEFB126 protein, their wives were significantly less likely than expected to become pregnant.

Previous studies have shown that two copies of the genetic variant may be found in up to one quarter of men around the world, with about half of all men having one copy. The DEFB126 protein coat helps sperm to swim through cervical mucus and evade the woman’s immune system, as well as enabling it to attach to the walls of fallopian tubes.

The study showed, however, that men with two copies of the variant produced sperm that were less able to swim through a substitute to cervical mucus, hyaluronic acid gel. In macaques, it has already been shown that this protein is important in evading the immune system and the researchers believe the protein coat plays the same role in humans. Commenting on the study, Dr Allan Pacey, senior lecturer in Andrology at the University of Sheffield, said: ‘We actually understand very little about the subtle molecular events which occur in sperm as they make their journey through the woman’s body to fertilise an egg’. The research was published in the journal Science Translational Medicine. If replicated in future studies, these findings promise to guide choices about the timing and type of assisted reproduction interventions—and further hint at the possibility of treating sperm from del/del homozygotes to promote fertility.

A gene which helps sperm bind to an egg has been identified by scientists. Sperm-to-egg binding is an essential process during fertilization and although the preliminary studies were performed on mice, the gene may represent a new target for infertility treatments. Sperm from mice that had the gene switched off were only able to fertilise eggs from female mice three percent of the time compared to 80 percent fertilisation success in normal mice.

The gene codes for a protein called PDILT which helps another gene product to form and assemble correctly and then to reach the surface of a sperm. Once this happens the sperm is able to navigate the uterus and oviduct and penetrate the sticky outer layers of an egg. The study, which is published in PNAS (Proceedings of the National Academy of Sciences), also demonstrates the importance of cumulus cells, a cluster of cells that surround and protect the egg, as their presence allows sperm to bind to their target. Sperm from mice that had their PDILT gene switched off would not bind to a bare egg, but would bind to an egg surrounded by cumulus cells.

Co-author Dr Adam Benham from Durham University in the UK said that the PDILT protein is ‘an essential part of the navigation system of sperm. 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’. A question now for the scientists is whether the PDILT gene has as much importance in human fertility as it does in mice. ‘Mutations in the gene may be responsible for unexplained male fertility problems and further research may aid more effective IVF treatment‘, said Dr Benham.

Source References:

http://stm.sciencemag.org/content/3/92/92ps31.abstract

http://www.bionews.org.uk/page_142955.asp

http://www.itv.com/news/update/2012-05-01/scientists-discover-new-gene-key-to-fertility/

http://www.bionews.org.uk/page_102705.asp

 

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