Spray of zinc marks fertilization

Outpouring of the metal kicks off embryonic development

5:14pm, May 5, 2011
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Sex is often associated with metaphorical fireworks, but there’s a real shower of sparks at the moment of conception. Scientists have witnessed mammalian eggs explosively releasing zinc atoms just after fertilization in a series of brief, intense outbursts that appear to jumpstart embryonic development.

The research, reported in an upcoming ACS Chemical Biology, reveals new details about how a single cell eventually becomes a full-blown organism and highlights that metals such as zinc can orchestrate major cellular events. In living things, zinc is better known for supporting roles, such as stabilizing a protein's conformation or assisting enzymes to spur chemical reactions forward.

“This really shows that elements, that chemistry, is in control of biology in a way we haven’t thought about,” says reproductive biologist Teresa Woodruff of Northwestern University in Chicago.

Before being released from the ovary, an egg has about 12 hours to prepare for fertilization. The egg must reduce its genetic material by half; the basic choreography of the ensuing chromosomal dance, known as meiosis, is well understood. But scientists are still working out the details of how an egg prepares its genetic material for fertilization.

It’s now clear that zinc plays an important role. Near the end of the 12-hour window, a mouse egg takes up more than 20 billion zinc atoms. This seems to signal the egg to sit tight, and the cell becomes quiet. But once a sperm hits its mark, the zinc bursts of out the egg.

These outbursts are dynamic, says Woodruff, who calls them zinc sparks. She did the research with colleagues at Northwestern and Argonne National Laboratory. In eggs of mice and two kinds of monkey, the team observed between one and five explosive bursts of zinc during the 90 minutes after fertilization. The release of the metal, which is linked to fluctuating levels of calcium, appears to signal the fertilized egg’s readiness to grow into a multicellular blob, and eventually an embryo. The team confirmed zinc’s role by manipulating the egg’s access to the metal.

The research hints that zinc may play a much broader role in biology than it’s given credit for, says developmental biologist Stephen Stricker of the University of New Mexico. “Who knows? Perhaps there’s a whole new zinc-signaling story out there,” he says. “This is exciting work and a really beautiful study.”

Researchers who have spent their careers focused on zinc find the work intriguing but aren’t surprised that zinc is acting as more than a sidekick to proteins. In fact, zinc is already known to play an important role on the male reproductive side of things, says biochemist Glen Andrews of the University of Kansas Medical Center in Kansas City. The male prostate contains some of the highest zinc concentrations of any tissue in the body; the metal is thought to help keep ejaculate stored there from coagulating before it’s released. “Zinc has many more roles than we imagined,” says Andrews. “Everybody needs it.” 

Untitled from Science News on Vimeo.

After mouse eggs are fertilized, they eject billions of zinc atoms, seen here in video captured using a synchrotron x-ray microscopy technique.
Credit: A.M. Kim et al/ACS Chemical Biology 2011

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