At least under a fluorescence microscope, new life is actually born in a spark. The moment the sperm touches the egg, billions of zinc atoms are ignited on the cell surface.
This spectacular miniature fireworks show was first documented in 2016 during human fertilization.
"Remarkable." Teresa Woodruff, a medical researcher at Northwestern University, said at the time, "We only found zinc sparks on mouse germ cells five years ago, and it was breathtaking to see the zinc fire star bursting out of human eggs." (Teresa Woodruff now works at Michigan State University.
Detailed explosion of zinc sparks at fertilization in a human egg. (Northwestern University)
Now the researchers have found that this chemical reaction during conception may be a conservative feature of vertebrates.
In addition to humans and mice, sparks have also been observed in the fertilized eggs of macaques and cattle. A new study has just seen atomic-scale fireworks in the African clawed frog (Xenopus laevis), meaning the phenomenon is at least as old as when frogs and mammalian ancestors parted ways 300 million years ago.
When zinc bursts, it binds to molecular tags in the reaction, causing them to emit a fiery flash of light under a fluorescence microscope.
Northwestern University biochemist John Seeler and colleagues chose to study African clawed frogs because they were so suitable in size and richness.
"The frog Xenopus has 15 times the egg diameter of mice and allows for more in-depth study of the dynamics of the zinc atomic flow."
Using powerful imaging techniques such as X-ray fluorescence microscopy and electron microscopy, the interdisciplinary team was able to see how frog eggs store zinc in microscopic pores along their surfaces. They measured that these storage bubbles contained 10 times more zinc than the rest of the egg — ready to explode when fertilized.
The researchers also detected that the eggs also released large amounts of manganese, which had not been seen in any other animal. They now hope to re-examine the manganese content of mouse eggs.
"We often think of genes as key regulators, but the work shows that atoms like zinc and manganese are critical to the first step of development after fertilization," Woodruff said of the new study.
Studies in mice have shown that zinc has several effects. It switches the cell cycle in an egg from meiosis to mitosis. This allows the egg to begin to develop into an embryo.
Zinc also creates a physiological barrier that prevents other sperm from joining. The same seems to be true of manganese, as Seeler's team showed that both elements inhibit fertilization around the egg.
The size of the zinc spark also reveals the quality of the resulting embryo, which is a very useful indicator of in vitro fertilization (IVF) techniques.
Thomas O'Halloran, a molecular biologist at Michigan State University, said: "This work may help us understand the interaction of zinc and human fertility in the diet." What we're finding is something new, the transition metal being used by cells to fulfill the initial function in an organism's life. ”
Their study was published in Nature Chemistry.
https://www.sciencealert.com/the-biological-fireworks-sparked-by-fertilization-are-at-least-300-million-years-old