Rewriting evolutionary history and shape future health studies

Date:
April 8, 2021
Source:
Michigan State University
Summary:
The network of nerves connecting our eyes to our brains is
sophisticated and researchers have now shown that it evolved much
earlier than previously thought, thanks to an unexpected source:
the gar fish.



FULL STORY ==========================================================================
The network of nerves connecting our eyes to our brains is sophisticated
and researchers have now shown that it evolved much earlier than
previously thought, thanks to an unexpected source: the gar fish.


========================================================================== Michigan State University's 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.

"It's the first time for me that one of our publications literally
changes the textbook that I am teaching with," said Braasch, as assistant professor in the Department of Integrative Biology in the College of
Natural Science.

This work, published in the journal Science on April 8, 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.

And this work, which was led by researchers at France's Inserm public
research organization, does more than reshape our understanding of the
past. It also has implications for future health research.

Studying animal models is an invaluable way for researchers to learn
about health and disease, but drawing connections to human conditions
from these models can be challenging.



========================================================================== 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,"
Braasch said.

"That's one of the reasons that people thought it was a new thing in tetrapods." Braasch 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 Braasch and his team are working to
better understand gar biology and genetics.

That, in turn, is why Inserm's researchers sought out Braasch for
this study.

"Without his help, this project wouldn't have been possible," said Alain Che'dotal, 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."
To do the study, Che'dotal and his colleague, Filippo Del Bene, used a groundbreaking technique to see the nerves connecting eyes to brains in
several different fish species. This included the well-studied zebrafish,
but also rarer specimens such as Braasch's gar and Australian lungfish
provided by a collaborator at the University of Queensland.



==========================================================================
In a zebrafish, each eye has one nerve connecting it to the opposite
side of the fish's brain. That is, one nerve connects the left eye to
the brain's right hemisphere and another nerve connects its right eye
to the left side of its brain.

The other, more "ancient" fish do things differently. They have what's
called ipsilateral or bilateral visual projections. Here, each eye has
two nerve connections, one going to either side of the brain, which is
also what humans have.

Armed with an understanding of genetics and evolution, the team could
look back in time to estimate when these bilateral projections first
appeared. Looking forward, the team is excited to build on this work to
better understand and explore the biology of visual systems.

"What we found in this study was just the tip of the iceberg," Che'dotal
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 Che'dotal 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 Braasch of another trend.

"We're finding more and more that many things that we thought evolved relatively late are actually very old," Braasch 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." ========================================================================== Story Source: Materials provided by Michigan_State_University. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Robin J. Vigouroux, Karine Duroure, Juliette Vougny, Shahad Albadri,
Peter Kozulin, Eloisa Herrera, Kim Nguyen-Ba-Charvet, Ingo Braasch,
Rodrigo Sua'rez, Filippo Del Bene, Alain Che'dotal. Bilateral
visual projections exist in non-teleost bony fish and predate the
emergence of tetrapods. Science, 2021 DOI: 10.1126/science.abe7790 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/04/210408163439.htm

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