Juno molecule - Fertility's Missing Link?


For decades, scientists have sought out ways to make the coupling of sperm and egg in fertility therapies more successful. The discovery of the Juno molecule by British researchers early in 2014 may provide the last missing link to a far brighter and more successful future in IVF. Thanks to this discovery, along with the discovery of a related molecule by Japanese researchers a decade ago, we have now identified the key components in bringing egg and sperm together – the “hardware” that allows these two cells to merge. Without these molecules, the coupling of egg and sperm literally cannot happen. With them, we see the potential for a live birth, nine months down the road. Small wonder, then, that the discovery of the Juno molecule has been hailed as nothing short of a miracle by the fertility community.

What is the Juno Molecule?

In 2005, Japanese fertility researchers achieved a major breakthrough. They had discovered a protein molecule which sits on the surface of sperm cells. Their research indicated that this protein, which they named Izumo1 after a Japanese marriage shrine, played a part in the coupling of sperm and egg. Since this kind of protein works by connecting with a matched partner, researchers around the world immediately set out in search of that partner – a matching protein on the surface of the unfertilized egg cell. That partner, which has since been dubbed the Juno molecule (after the Roman goddess of fertility) was found by researchers in the UK in 2014.

It took nearly ten years, in part because the connection between the two molecules is very weak; their exact workings proved elusive, and this particular aspect of the reproductive cycle had never previously been mapped any species. The Juno molecule is one of several molecules in the folate receptor family, which mediate the delivery of other substances to the interior of a cell.

How was the Juno Molecule's Role Discovered?

It has been known for some time that something with the molecular structure of Juno existed; the molecule was first discovered in the year 2000, but its specific function relative to human reproduction was not immediately obvious. A lengthy application of the scientific process was needed to determine, and ultimately to prove, the Juno molecule's role in reproduction. That discovery, coupled with that of the role of Izumo1, marked the first scientific understanding of this stage of the reproductive process in any living organism.

Prior to the discovery of Juno's specific role in the fertilization process, generations of male laboratory mice had been bred to produce sperm which lacked the Izumo1 molecule. They were entirely infertile. Their sperm were unable to form the necessary bond with egg cells cultivated from healthy, unaltered female laboratory mice, and the reproductive cycle never got started. The verification of Juno's role culminated in similar experiments with female mice, who were bred with eggs that lacked the Juno molecule. They were likewise infertile; their eggs were unable to form the necessary bond with healthy sperm cells from unaltered male laboratory mice. This was the breakthrough moment in the ongoing, worldwide research initiative.

What are the Potential Applications of the Juno Molecule?

The potential applications of the Juno molecule for further medical research are as numerous as they are profound. They cover a broad spectrum – from fertility treatments, to potential new avenues of contraception. At present, it is simply too soon since the discovery of Juno (also known as folate receptor 4, folate receptor delta, or IZUMO1R) to guess at the full potential range of applications for related treatments. For example, some cases of infertility in women may be due to a lack, or an insufficiency, of the Juno protein. The evaluation of such a possibility requires additional data, and work is ongoing in the field of fertility research.