Biological fireworks triggered by fertilization are at least 300 million years old

New life springs up, at least under a fluorescence microscope. As the sperm touches the egg, billions of zinc atoms ignite on their now adherent surfaces.

This amazing but small-scale phenomenon was first observed in human pollination in 2016.

“It was fantastic,” Northwestern University medical researcher Theresa Woodruff said at the time. “We only detected a spark of zinc five years ago in a mouse, and to see zinc radiate in a splash from every human egg was amazing.” (Woodruff now works at Michigan State University.)

Researchers have now discovered that this pregnancy chemistry can be a conserved trait of fertilization in vertebrates or animals with a spine.

The dramatic flash of fertilization in human oocytes. (Northwestern University)

as well as inside humans and mice (mouse muscle), these zinc-enriched fireworks have been observed in macaques and mated cows (bull head) eggs. A new study has just seen an explosion of zinc in the African clawed frog (Xenopus laevis) also, which means that the phenomenon is at least as old as when the ancestors of frogs and mammals diverged evolutionarily, about 300 million years ago.

When zinc bursts through an egg under study, it binds to molecular markers in a reaction that causes them to glow in a light flash under a fluorescence microscope (pictured above).

Northwestern University biochemist John Siler and his colleagues chose to examine these biochemical sparks in the African clawed frog because of their size and abundance.

“Diameter Xenopus The egg count is 15 times that of mouse eggs, which allows for further study of the dynamics of zinc flux, ”the team wrote in their paper.

frog. (Brian Garnett Photography / Moment / Getty Images)

Using powerful imaging technologies such as X-ray microscopy and electron microscopy, the multidisciplinary team were able to see how eggs store zinc in microscopic storage compartments along their surface. They measured that these storage vesicles contained 10 times more zinc than the rest of the egg – ready to burst in response to fertilization.

The researchers also detected a significant release of manganese and zinc in the eggs of the frogs, which was not observed in any of the other animals. They now hope to check manganese levels in mice.

“We often think of genes as key regulatory factors, but our work has shown that atoms like zinc and manganese are essential for the early stages of development after fertilization,” Woodruff said of the new study. .

Detailed explosion of zinc sparks during fertilization in a human egg. (Northwestern University)

Research in mice suggests that zinc volatility serves several purposes. It magics the cell cycle in the egg of meiosis – which involves cell division that results in sex cells with only half of a set of chromosomes – in mitosis – which produces cells with a full set of chromosomes. This allows the egg to start developing into an embryo.

Zinc also produces physiological mass to prevent other sperm from joining in the fun. The same seems to be true for manganese, as Seiler and his team have shown that both elements inhibit fertilization around the egg.

The size of the zinc sparks also reveals the quality of the resulting embryo, which is a very useful indicator of in vitro fertilization (IVF).

“This work can help us understand the interplay between dietary zinc status and human fertility,” said Thomas O’Loran, molecular biologist at Michigan State University. “[It supports] An emerging image that cells use transition metals to regulate some of the earliest decisions in an organism’s life.

Their research has been published in chemistry of nature.