Fertilization Launches Zinc Fireworks

“Beautiful to see, orchestrated much like a symphony” –
This is how a fertilized cell announces a new individual

Fireworks with a function: that is how an amazing show could be described. When sperm meets egg, billions of zinc ions are released from special containers in the egg, switching on a host of changes and announcing the creation of a new individual life.

It was a picturesque discovery that Northwestern University announced on December 14, 2014: “Stunning Zinc Fireworks When Egg Meets Sperm.” Life begins with fireworks! The press release even included a video clip showing how the zinc ions “explode” in the cell during waves of “molecular fireworks” upon fertilization. They called them “zinc sparks” and said they are programmed for this very moment:

“On cue, at the time of fertilization, we see the egg release thousands of packages, each dumping a million zinc atoms, and then it’s quiet,” said Thomas V. O’Halloran, the other corresponding author. “Then there is another burst of zinc release. Each egg has four or five of these periodic sparks. It is beautiful to see, orchestrated much like a symphony. We knew zinc was released by the egg in huge amounts, but we had no idea how the egg did this.”

Like other metals, zinc can be toxic to a cell. A host of metalloproteins and enzymes are tasked with safeguarding the cell and gently handling zinc, iron, manganese and other metals required for essential life processes. The scientists at Northwestern identified the rocket launchers in the egg that wait for the signal that a sperm has entered:

After inventing a novel vital fluorescent sensor for live-cell zinc tracking, scientists discovered close to 8,000 compartments in the egg, each containing approximately one million zinc atoms. These packages release their zinc cargo simultaneously in a concerted process, akin to neurotransmitter release in the brain or insulin release in the pancreas.

An article in Evolution News, “How Sex Is Like Fireworks” (19 Dec 2014), noted several uncanny resemblances to man-made fireworks shows. It’s metals that give fireworks their bright colors; the show is programmed; and the explosives are stored in safe containers till use. Most important of all, fireworks shows are reserved for very special occasions. And what is more special than the start of a new individual life?

Paper: 15 Dec 2014 by Que et al. as “Quantitative mapping of zinc fluxes in the mammalian egg reveals the origin of fertilization-induced zinc sparks,” Nature Chemistry volume 7, pages 130–139 (2015).

As beautiful as the “zinc sparks” are, the fireworks are not just for show. The authors believe that they play a key role in preventing additional sperm from entering the egg, which would result in “polyspermy” (too many chromosomes). The sudden zinc release may also play additional unknown roles that go beyond fertilization.

These cortical zinc-rich vesicles released during egg activation have a number of potential functions during fertilization. The changes in distribution and quantity of these vesicles throughout maturation and activation mirror those of CGs [Note: cortical granules (CGs) are”Golgi-derived vesicles distributed throughout the oocyte cortex during oogenesis”]. These secretory vesicles are released at fertilization and contain biochemical species, including enzymes, that modify the egg’s ZP [zona pellucida, an outer layer in the egg that hardens after fertilization] and thus play a role in the block to polyspermy. Intriguingly, one of the known CG proteins, the zinc metalloprotease ovastacin, has been shown to cleave the ZP glycoprotein ZP2 in a key step of zona hardening and prevention of polyspermy. Alternatively, zinc released by the egg could act directly on sperm to alter their function given the importance of zinc in mammalian sperm physiology. Thus metals released during the zinc spark and the cortical reaction may play a number of roles outside the cell.

What’s New

Scientists at Argonne National Laboratory recalled that the discovery at Northwestern “made international headlines” at the time. Working with Northwestern, Argonne Lab scientists used specialized equipment to announced this week that they have  extended the discovery. They conducted scans at unprecedented scales with specialized equipment that did not damage the delicate eggs of Xenopus frogs. “Scientists using the Advanced Photon Source show how ​‘zinc sparks’ — the showers of zinc ions released by mammalian eggs immediately after fertilization — also occur in amphibian eggs.”

These scans were performed at smaller scales — down to a few nanometers, about 100,000 times smaller than the width of a human hair — but found the same results: high concentrations of metals in pockets around the outer layer.

This can only mean one thing, the scientists conclude. God didn’t program and plan the fireworks show. Darwin did.

Now, Northwestern has teamed up with the U.S. Department of Energy’s (DOE) Argonne National Laboratory and Michigan State University (MSU) to reveal that these same sparks fly from highly specialized metal-loaded compartments at the egg surface when frog eggs are fertilized. This means that the early chemistry of conception has evolutionary roots going back at least 300 million years, to the last common ancestor between frogs and people.

Reporters Matthew Davenport and Andre Salles titled their report from Argonne, “A biological fireworks show 300 million years in the making.” Note: 300 million years were not observed in the research. The paper only calls the process “an evolutionarily conserved [unevolved] and functional feature of fertilization from amphibians to mammals.”

Paper: Seeler et al., “Metal ion fluxes controlling amphibian fertilization.” Nature Chemistry volume 13, pages 683–691 (21 June 2021).

Chuck in the Box makes another unwanted appearance.

Can we get Chuck out of here? He is not welcome. He’s like an unpopular mayor grabbing the mike at the end of the show and telling the audience how great a job he is doing, how he planned and paid for the performance, and why you should keep voting for him, when he has actually done nothing but lavish tax dollars on his own mansion. Time for some loud boos from the audience.

When the zinc sparks were first observed in 2014, it seemed like a mammalian phenomenon. Now we see the fireworks shows occur in frog eggs, too. Does that imply anything about evolution? Does it mean that Darwin’s Stuff Happens Law brought it into emergence 300 million Darwin Years ago? Of course not. Every sexually-reproducing creature that merges gametes has the challenge of preventing polyspermy. This is a great system to “orchestrate” numerous processes to prevent it, as well as to trigger other processes that must begin after fertilization. In fact, we should predict that zinc sparks will be found in even lower life forms that undergo sexual reproduction. That’s not evolution; that is design.

There are more reasons to stuff Chuck back in his box. Zinc sparks constitute a marvelously coordinated system that is irreducibly complex. Darwin couldn’t come up with just one of the enzymes in the CG or ZP or anywhere, let alone dozens or hundreds of them. Need we remind anyone that the probability of getting one average protein by chance is so low, you would need to wait longer than the assumed age of the universe? Read more about the “waiting time problem” at Evolution News.

Good News for Pro-Life Workers

The discovery of “fireworks” at fertilization is great news for pro-life workers. Many communities host a “Walk for Life” like the one last week in California (YouTube). What would people think if they knew that fertilization triggers a real fireworks show? Pro-lifers argue that life begins at fertilization. That is clearly evident with this news. There’s nothing like it. The process closes the door to any other sperm trying to enter. The unique genome of a new individual is set. From then on, everything else that happens is devoted to the development, maturation and nourishment of that unique individual. There is no other point downstream from fertilization that is so clearly a starting point for life.

Incidentally, to answer the LGBT community, it is two and only two gametes that merge: one male and one female. Two sperm don’t react like this. Two eggs don’t react like this. It takes one of each to set off the fireworks show. Sex is binary, and so is the gender that goes along with the genetic switches embedded in the X and Y chromosomes.

Pro-lifers should take this news, illustrate it and capitalize on it. People would be fascinated to learn about fireworks in the successfully-fertilized egg. It could become a visual aid to emphasize the fact that life begins at conception.