“Sticky” Egg Captures Sperm
A study by an international team of researchers published in the journal Science in August 2011 has found that it is the “sticky” egg that catches the sperm. The international research team said that their discovery should help couples who suffer from infertility problems in the future.
The study found that there is a particular type of sugar molecule the makes the outer coat of the egg “sticky,” helping the egg and sperm bind together.
In London, Imperial College’s Anne Dell stated that there is a big gap in fertility knowledge which has been filled by the study. Anne Dell and the rest of the research team are hopeful that ultimately the research findings should help people who cannot conceive. Dell collaborated with scientists from the universities of Missouri and Hong Kong, and the Academia Sinica in Taiwan.
Currently in Britain it is estimated that 1 out of every 7 couples has problems when it comes to conceiving a baby which happens for a range of reasons, however many of these reasons up to now have not been explained by medical science. Around the world it is estimated by the WHO (World Health Organisation) that up to 15% of couples of reproductive age are affected by fertility problems.
Before this latest study scientists knew that an egg is recognised by the sperm when proteins on the sperm make a match with a series of specific sugars in the outer coating of the egg. It is by this match being made successfully that then the egg and sperm will bind together and the sperm delivers its DNA to the inside fertilising the egg.
The study identified the sugar chain which is now known as the sialyl-lewis-x sequence (SLeX). Laboratory experiments with a variety of synthesised sugars confirmed that it is SLeX which binds the sperm to the egg.
The lead author of the research study, Poh-Choo Pang said that although clinical treatments are still a way off, the study has opened up new possibilities for addressing and understanding fertility problems faced by many couples. The team are excited by the new research and are looking forward to building on their work.
Egg Meets Sperm: The Female Side of the Story
The findings of another study: Egg Meets Sperm: The Female Side of the Story was published in October 2010. A research team from the Swedish medical university Karolinska Institutet, led by Luca Jovine, which collaborated with Prof. Tsukasa Matsuda at Nagoya University, Japan, and Dr. David Flot at the ESRF discovered the 3D structure of the egg’s receptor molecule that binds the sperm, called ZP3.
Luca Jovine said: “The results give a remarkable picture of the female side of fertilisation, but this is, of course, only half of the story. The next step will be to tackle the corresponding molecules on sperm that allow it to bind to the egg.”
Therefore from the “sticky” egg study we know that the sperm recognises the egg when certain proteins on the head of the sperm meet and match a series of specific sugar in the egg’s outer coating. From the Luca Jovine led study we know that the egg has this 3D receptor molecule, called the ZP3. Yet there is another study which has made an important breakthrough on sperm DNA integrity.
Sperm DNA Integrity
In 2010 researchers in Yale School of Medicine discovered a method to choose the spermatozoa (sperm) with the highest DNA integrity. In the natural fertilisation process the oocyte (egg) is responsible for choosing the best quality sperm.
However during IVF (in-vitro fertilisation) treatment clinicians could not be sure if they were injecting the best sperm into the egg for fertilisation. Previous semen analysis had focused on the sperm concentration and mobility, which was based on the assumption that if a man has a high sperm count and active sperm that he was fertile.
Yet this approach did not take into consideration the sperm’s ability to attach to the female gamete (egg, ovum). Gabor Huszar, M.D., director of the Sperm Physiology Lab, who was the senior author of the study said: “We have now found a biochemical marker of sperm fertility so that we can select sperm with high genetic integrity,”
Huszar and his team tested the concept that binding sperm to hyaluronic acid will select that sperm with high DNA integrity. Huszar’s conclusion is that the sperm which is selected by the hyaluronic acid binding is of comparable if not better quality that the sperm which the oocyte chooses during the natural fertilisation process.
He also likens sperm which has fragmented DNA to scratched CDs. They seem to be operational but when you play the CDs some information is missing. In the same way damaged sperm can be carrying chromosomal aberrations which may relate to genetic diseases.
These studies featured in this article are only a sample of the many fascinating studies around the topic of fertility. These scientific studies are remarkable and whether it is the potential improvements in IVF or a better understanding of the natural fertilisation process, we can be grateful to the scientists for their work which will no doubt help couples conceive over the coming years.
These scientific studies as well as other important relevant studies not featured in this article, offer increased hope to IVF (in-vitro fertilisation) patients and couples with previously medically unexplained fertility problems.