How Do Sperm Recognize Eggs? Mechanism Finally Found

By Breanna Draxler | April 16, 2014 12:01 pm

sperm eggs

It’s the stuff of 3rd-grade sex ed: sperm meets egg to make baby. But, surprisingly, scientists have actually been in the dark about one crucial step: how the two sex cells recognize each other amidst the fluid frenzy in the Fallopian tubes. Now researchers have announced that they’ve found the missing piece of this fertilization puzzle, and that the discovery could lead to individualized fertility treatments and hormone-free birth control.

Back in 2005, researchers found the first half of the the puzzle: a binding protein on the surface of sperm they called Izumol (after a Japanese marriage shrine). In the decade since then, scientists have been searching for Izumol’s counterpart on egg cells. Essentially, they’d found the plug but couldn’t locate the outlet.

Today researchers at Cambridge announced they’ve found that outlet: a receptor protein on the surface of the egg cell. They’ve found it on the eggs of pigs, opossums, mice and even humans.

Protein Match

Researchers found that the only receptor protein that matched up with the sperm protein was one that had already been discovered and named. Its true purpose had just been misunderstood. The receptor had been previously known as Folr4, and thought to be part of the folate-receptor family.

When researchers put unfertilized eggs in a petri dish and blocked their Folr4 receptors, sperm couldn’t latch on. And when researchers genetically modified female mice to lack Folr4, the mice were sterile.

And what’s even more, the discovery also helps explain how eggs limit themselves to just one sperm invader. By studying eggs fertilized in vitro,  researchers found that the Folr4 proteins had all been ejected from the surface of the cell by 30 minutes after fertilization and were floating around the membrane, no longer able to bind with the proteins on the sperm.

juno receptor protein unfertilized eggs

The Izumol protein on the surface of the sperm pairs up with the Folr4 (Juno) protein on the unfertilized egg. Once fusion occurs, the egg spits out the remaining Juno proteins to prevent multiple sperm from fertilizing the same egg. Image credit: Nature

Pregnancy on Demand

Understanding how the fertilization process starts is big news—it could lead to specialized fertility treatments as well as non-hormonal birth control. Such a crucial role calls for a name change: The researchers have now dubbed the protein Juno (in honor of the Roman goddess of marriage, or, perhaps, more appropriately, for the 2007 academy award-winning film of the same name).

A simple genetic test could determine if a woman’s infertility is due to a lack of Juno proteins, allowing her to skip all the preliminary fertility treatments that won’t work in her case, and cutting right to the manual injection of sperm. Likewise with contraception, knowing the critical role of this particular protein means that blocking it can render sperm powerless.

Now that scientists have found the two halves of this puzzle, which they published in Nature today, their next step is discovering what other proteins are at play when the sperm and egg actually fuse.


Top image credit: videodoctor/Shutterstock

CATEGORIZED UNDER: Health & Medicine, top posts
MORE ABOUT: sex & reproduction
  • Anmar Ahmed


  • Prentice Price

    OK, so now we know how the sperm finds the egg. Big deal! I want to know why it feels so good?

    • suresh apte

      you do not feel good when sperm meets an egg but long before that,just when you send them (sperms)off on their way to meet the egg.

  • johnclark1

    Nature made it feel good, Prentice, so you’d want to perform this otherwise disgusting dance of perversion. That’s why we’re here, and there’s so much sexual crime in the world. Let’s do it again!

  • Omar Grigorievich

    Hell yeah. Time to welcome a new generation of contraceptives. Maybe one for us men.

    • Ruth Ramirez-Locke

      Male contraceptives are already in the works. Look up Vasalgel, very interesting research.

    • Ugochukwu Opara

      Glad someone is on the same page!

  • Alex Lee

    How does anything work? It is programmed by the Almighty!

    • Don’t Even Try It!


    • NHealy

      Or the easter talking snake

  • suresh apte

    why would it take as long as 30 minutes to disable fertilised egg for additional fertilization?what is the probability that once fertilised egg is again fertilised in that 30 minute period?

    • Don’t Even Try It!

      If you are are whore, pretty damned good, I would say.

    • Leah Rachel Bordow

      I says “by 30 minutes”. After having had university biology, that means that the proteins start to eject from the point of contact and within a half hour the proteins that haven’t been latched onto will have detached. However, they also never said they tracked the proteins from the point of contraception, which could mean that they only checked the Folr4 after the half hour and noticed they were all gone. It doesn’t specify, but I would like to see that data for myself. If there are still proteins attached to egg the for the sperms protein to attach to the egg, it could lead to maternal twins. Fraternal twins means two eggs and two sperm. Maternal would result when the egg cell splits after two sperm attach if the protein research shows it.

      • Gregory M. Buchold

        Good thought that the researchers would use 30 min, 1hr, 2hr time-points. The “block to polyspermy” has several component processes that run simultaneously including hardening the egg exterior.

  • Don’t Even Try It!

    OK, so what prevents multiple insertions within the 30 minute window of opportunity?

    • JustCheyChey

      I think you have problems with women. Just saying.

  • Leah Rachel Bordow

    Now I wanna know how does this process differ with maternal and fraternal twins.

    • Melodi Foster

      There are not maternal and fraternal twins, either identical and fraternal. Identical: one eggs is fertilized and splits. Fraternal: two eggs are fertilized by two sperm.

  • ConnerSeth

    How long before these new contraceptives become prevalent or even more than an idea?

  • Daguy8t4

    Seems like a programmer scripted this to work in this 1,2,3 type of manner …seems very precise rather than random…and no I’m not religious

  • Ashish Rao

    If there is certain proteins on male gamete of a spices which matches with that of female gamete, which further leads to fertilisation. My question is that than how fertilisation take place between male donkey and female horse to give birth #mule?


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