Researchers at Cambridge University in England have unlocked the secret of attraction between sperm and egg at the exact moment of conception. Now that this egg and sperm recognition mechanism has been revealed, there is hope it will lead to other medical breakthroughs that will aid infertility diagnosis and provide treatment options not available today.

The Cambridge study answers two important questions:

  1. In the sperm-filled frenzy inside the fallopian tube after ejaculation, how do the egg and sperm recognize each other?
  2. How is it that just one sperm enters the egg when he's got millions of sperm?

Fertilization

The answers to both questions lie in two proteins — one male, one female — that have been affectionately named Izumol, after a Japanese shrine to marriage, and Juno, a Roman goddess of marriage.

Izumol was discovered in 2005. It was understood he is a binding type of protein covering the outer surface of a sperm cell but nobody knew what it was he was supposed to bind to. Juno's existence on the surface of the egg was also already known, when the Cambridge study began. She even had a name — Folr4 — because she was believed to be a part of a family of proteins known as folate receptors. Other than that, nobody really knew what her purpose was.

The Cambridge researchers tested Folr4 in two ways:

  1. On unfertilized eggs in a petri-dish culture — When an egg's Folr4 receptors were blocked, sperm cells could not attach to or penetrate the egg.
  2. On female mice genetically modified so they did not produce Folr4 — They were all sterile.

The petri-dish experiments produced the same results on the eggs of opossums, pigs, and humans, suggesting the protein plays a significant role in mammalian reproduction. They also learned a lot more about Izumol.

What the researchers discovered is that Folr4 (now Juno) attracts something much more important than just folate — she attracts Izumol. Juno's Folr4 receptors work like a perfectly fitted glove to the "hands" of Izumol's binding proteins.

Furthermore, once Juno has found a fit to one sperm's Izumol proteins, the egg expels all its other Juno receptors, making it impossible for other sperms to attach to the egg.

All sorts of good things are anticipated to come from this discovery:

  • A simple genetic test for Juno proteins that could quickly pinpoint a woman's cause of infertility.
  • In vitro fertilization without the need for trial-and-error attempts at other fertility treatments.
  • Effective birth control that doesn't involve hormone manipulation.

Now that the attraction between Juno and Izumol is understood, the research team is looking forward to exploring the roles other proteins might play in the fusion of egg and sperm.


Source: Draxler, Breanna. "How Do Sperm Recognize Eggs? Mechanism Finally Found." D-brief / Discover Magazine. Kalmbach Publishing Co. Apr 16, 2014. Web. Apr 22, 2014.