Molecular 'barcode' determines which sperm reaches the egg

Protein channels help determine the 'winning sperm' that rises above the other millions to reach the egg, new research has shown.

Sperm tails are lined with protein channels containing pores that allow the entry of calcium, playfully dubbed by researchers as their 'racing stripes'. Researchers at Yale University used a novel 3D molecular imaging technique to visualise this protein within the reproductive tract of female mice after mating, showing which type of protein is essential for sperm to reach the egg.

The team pulished their findings in eLife, stating '[this research] could help identify new targets for contraception and improve current strategies for assisted reproduction'. 

The sperm channels are made up of four protein subunits, CatSper1 to CatSper4, which together ultimately control the motility and navigation of the sperm. They found that the sperm that made it to the oviduct all had intact CatSper1, whereas sperm with broken down CatSper1 were left behind. 

Since CatSper1 is necessary for functional sperm, blocking it may be an effective non-hormonal contraceptive with minimal side effects, claims Dr Jean-Ju Chung, assistant professor of cellular and molecular physiology at Yale School of Medicine and lead author on the study. Alternatively, since mutations have been found in CatSper genes of infertile men, they may become a target for fertility treatments. 

They also found these 'winning sperm' have already lost a cap-like structure called the acrosome in the sperm head, which is proposed to indicate the sperm preparing to fertilise the egg.

The team suggest this new imaging platform will allow scientists to learn more about the fertilisation process in a model more relevant to the true reproductive process than a Petri dish. They say future studies must address what happens once the CatSper1 protein is broken down, and how this impacts the movement and lifespan of sperm.