Discovery of “literally changing textbooks”

Behold, Gar’s brain. In this microscopic image, the left hemisphere of the brain fluoresces green and the right hemisphere glows magenta. However, at the bottom of the image, nerves of both colors can be seen connecting to both hemispheres. This shows that both eyes of Gar are connected to both sides of the brain, similar to the human eye. Credit: RJ Vigouroux Reprinted with other permission. Science 372: eabe7790 (2021)

The neural network that connects our eyes to the brain is sophisticated, and researchers have shown that it has evolved much faster than previously thought, thanks to an unexpected source of information, Garfish. It was.

Ingo Braasch of Michigan State University helped an international research team show that this connection scheme already existed in ancient fish at least 450 million years ago. It makes it about 100 million years older than previously believed.

“One of our publications is the first to literally change the textbook I teach,” said Blush, assistant professor of integrated biology at the Faculty of Natural Sciences.

This work published in the journal Science April 8 also means that this type of eye-brain connection exists even before land-dwelling animals. The existing theory was that this connection first evolved in terrestrial life, from which it was passed on to humans, and scientists believed it would be useful for our perception of depth and 3D vision.

And this study, led by researchers at the French Inserm public research institute, does more than just reshape the understanding of the past. It will also affect future health research.

Studying animal models is an invaluable way for researchers to learn about health and illness, but it can be difficult to derive a connection to human condition from these models.

Zebrafish, for example, is a popular model animal, but its eye and brain wiring is very different from that of humans. In fact, it helps to explain why scientists thought human connections first evolved in limb terrestrials, or tetrapods.

“Modern fish, they don’t have this kind of eye-brain connection,” Blush said. “That’s one of the reasons people thought it was new to Tetrapod.”

Braasch is one of the world’s leading experts in various types of fish known as gar. Gar evolved more slowly than zebrafish. In short, Gar is like the last common ancestor shared by fish and humans. These similarities make gar a powerful animal model for health research. That’s why Braasch and his team are working to better understand gar’s biology and genetics.

Therefore, Inserm researchers searched for Braasch for this study.

“Without his help, this project would not have been possible,” said Alain Shedotal, head of research at Inselm and group leader at the Vision Institute in Paris. “We couldn’t get the spotted gar, a fish that doesn’t exist in Europe and occupies an important position in the tree of life.”

To conduct the study, Chédotal and his colleague Filippo Del Bene used breakthrough technology to observe the nerves that connect the eyes and brain of several different fish species. This included not only well-studied zebrafish, but also rare specimens such as brushed gar and Australian lungfish provided by collaborators at the University of Queensland.

In zebrafish, each eye has one nerve that connects to the other side of the fish’s brain. That is, one nerve connects the left eye to the right hemisphere of the brain and the other nerve connects the right eye to the left side of the brain.

Another, more “ancient” fish does things differently. They have what is called ipsilateral or bilateral visual projections. Here, there are two neural connections in each eye, one on both sides of the brain. This is also what humans have.

Armed with an understanding of genetics and evolution, the team was able to look back in time to estimate when these bilateral predictions first appeared. Looking forward, the team is excited to build on this task to better understand and explore the biology of the visual system.

“What we found in this study was just the tip of the iceberg,” Shedotal said. “When I announced the first results, I was very motivated to see Ingo’s enthusiastic reaction and warm support. I can’t wait to continue the project with him.”

Both Braasch and Chédotal pointed out how powerful this study is, thanks to the powerful collaboration that allowed the team to inspect so many different animals.

The study also reminded Blush of another trend.

“Many of the things we thought evolved relatively slowly are becoming more and more known to be really very old,” Blush said. “When I see these weird fish and understand how old the old parts of my body are, I learn something about myself. In our comparative anatomy class, a new twist this semester. I’m excited to talk about the evolution of the eyes. ”

Fish reveals the secret of limb regeneration

For more information:
“Bone fish other than bone fish have bilateral visual projections, which exist before the appearance of tetrapods.” Science (2021).… 1126 / science.abe7790

Courtesy of Michigan State University

Quote: The discovery of “literally changing textbooks” (April 8, 2021) was taken from on April 8, 2021. Did.

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Discovery of “literally changing textbooks”

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