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Braasch Lab Research Shows Much Earlier Eye/Brain Nerve Connection Than Previously Believed

Ingo Braasch has helped an international research team show that this connection scheme was already present in ancient fish at least 450 million years ago. That makes it about 100 million years older than previously believed. He said, “It’s the first time for me that one of our publications literally changes the textbook that I am teaching with."

This work, published April 8 in the journal Science, also means that this type of eye-brain connection predates animals living on land. The existing theory had been that this connection first evolved in terrestrial creatures and, from there, carried on into humans where scientists believe it helps with our depth perception and 3D vision.

Zebrafish are a popular model animal, for example, but their eye-brain wiring is very distinct from a human’s. In fact, that helps explain why scientists thought the human connection first evolved in four-limbed terrestrial creatures, or tetrapods.

“Modern fish, they don’t have this type of eye-brain connection,” Ingo said. “That’s one of the reasons that people thought it was a new thing in tetrapods.”

Ingo is one of the world’s leading experts in a different type of fish known as gar. Gar have evolved more slowly than zebrafish, meaning gar are more similar to the last common ancestor shared by fish and humans. These similarities could make gar a powerful animal model for health studies, which is why he and his team are working to better understand gar biology and genetics.

Inserm, France's public research organization led the work and sought out Ingo for this study. “Without his help, this project wouldn’t have been possible,” said Alain Chédotal, director of research at Inserm and a group leader of the Vision Institute in Paris. “We did not have access to spotted gar, a fish that does not exist in Europe and occupies a key position in the tree of life.”

“What we found in this study was just the tip of the iceberg,” Chédotal said. “It was highly motivating to see Ingo’s enthusiastic reaction and warm support when we presented him the first results. We can’t wait to continue the project with him.”

Both Braasch and Chédotal noted how powerful this study was thanks to a robust collaboration that allowed the team to examine so many different animals, which Braasch said is a growing trend in the field.

The study also reminded Ingo of another trend.

“We’re finding more and more that many things that we thought evolved relatively late are actually very old,” he said, which actually makes him feel a little more connected to nature. “I learn something about myself when looking at these weird fish and understanding how old parts of our own bodies are. I’m excited to tell the story of eye evolution with a new twist this semester in our Comparative Anatomy class.”

(Photo courtesy of Solomon David, Braasch Lab.)