A stunning explosion of zinc fireworks occurs when a human egg is activated by a sperm enzyme, and the size of these "sparks" is a direct measure of the quality of the egg and its ability to develop into an embryo, according to new research from Northwestern Medicine.

The discovery has potential to help doctors choose the best eggs to transfer during in vitro fertilization (IVF), the scientists said. This is the first time the zinc sparks have been documented in a human egg.

Scientists activated the egg by injecting a sperm enzyme into the egg that triggers calcium to increase within the egg and zinc to be released from the egg. (The eggs in the study were not fertilized with actual sperm because that is not permitted in human research under federal law.)

"It was remarkable," author said. "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. "All of biology starts at the time of fertilization, yet we know next to nothing about the events that occur in the human. This discovery required a unique partnership between biologists and chemists and non-federal dollars to support the research."

The study will be published in Scientific Reports.

As the zinc is released from the egg, it binds to small molecule probes, which emit light in fluorescence microscopy experiments. Thus the rapid zinc release can be followed as a flash of light that appears as a spark.

Eggs compartmentalize and distribute zinc to control the development of a healthy embryo. Over the last six years this team has shown that zinc controls the decision to grow and change into a completely new genetic organism.

"This is an important discovery because it may give us a non-invasive and easily visible way to assess the health of an egg and eventually an embryo before implantation," said co-author.

"There are no tools currently available that tell us if it's a good quality egg," author said. "Often we don't know whether the egg or embryo is truly viable until we see if a pregnancy ensues. That's the reason this is so transformative. 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."

In a companion paper published in Scientific Reports, a zinc spark is shown at the precise time a sperm enters a mouse egg. This discovery was made by, a postdoctoral fellow at Northwestern. Researcher said little is known about the events that occur at the time of fertilization, because it is difficult to capture the precise time of sperm entry.

http://www.northwestern.edu/newscenter/stories/2016/04/radiant-zinc-fireworks-reveal-quality-of-human-egg.html