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Human eggs celebrate insemination with flash of zinc fireworks

"We discovered the zinc spark just five years ago in the mouse, and to see the zinc radiate out in a burst from each human egg was breathtaking," said researcher Teresa Woodruff.

By Brooks Hays
Human eggs celebrate insemination with flash of zinc fireworks
A diagram shows the initialization of the zinc sparks, which are triggered when an egg is activated by sperm enzymes. Photo by Nan Zhang, et al./Scientific Reports

CHICAGO, April 26 (UPI) -- When the romantic sparks fly, zinc sparks sometimes fly, too.

According to new research out of Northwestern University, eggs reveal their relative fertility by radiating zinc fireworks when successfully inseminated.

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When the sperm enzyme triggers these zinc fireworks, the relative size of the sparks is an indication of the egg's health or reproductive potential -- the likelihood it will successfully generate a fetus.

It's the first time scientists have observed zinc sparks in a human egg, and researchers believe it will help fertility doctors more accurately select healthy eggs.

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"This means if you can look at the zinc spark at the time of fertilization, you will know immediately which eggs are the good ones to transfer in in vitro fertilization," senior co-author Teresa Woodruff, an expert in ovarian biology at Northwestern, said in a news release. "It's a way of sorting egg quality in a way we've never been able to assess before."

Woodruff and her colleagues detailed their discovery this week in a paper published in the journal Scientific Reports.

"It was remarkable," Woodruff added. "We discovered the zinc spark just five years ago in the mouse, and to see the zinc radiate out in a burst from each human egg was breathtaking."

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The sparks witnessed by researchers aren't symbolic, they're actual flashes of light.

An egg's zinc -- which it stores and uses to transform into a new genetically unique organism -- binds to small molecular probes when released upon the egg's activation. As it binds, the probes emit a spark-like flash of fluorescence visible via microscopy imaging.

"These fluorescence microscopy studies establish that the zinc spark occurs in human egg biology, and that can be observed outside of the cell," explained Tom O'Halloran, the study's other senior author.

Researchers say their latest findings will help doctors know which eggs are viable and which are not.

Zinc Spark from Northwestern News on Vimeo.

"If we have the ability up front to see what is a good egg and what's not, it will help us know which embryo to transfer, avoid a lot of heartache and achieve pregnancy much more quickly," said co-author Dr. Eve Feinberg, a physician at Fertility Centers of Illinois and an assistant professor of obstetrics and gynecology at Northwestern's Feinberg School of Medicine.

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