Learning from a 'living fossil'

Date:
August 30, 2021
Source:
Michigan State University
Summary:
As we live and breathe, ancient-looking fish known as bowfin are
guarding genetic secrets that that can help unravel humanity's
evolutionary history and better understand its health.



FULL STORY ========================================================================== [Bowfin fish (stock | Credit: (c) mirecca / stock.adobe.com] Bowfin fish
(stock image).

Credit: (c) mirecca / stock.adobe.com [Bowfin fish (stock | Credit:
(c) mirecca / stock.adobe.com] Bowfin fish (stock image).

Credit: (c) mirecca / stock.adobe.com Close As we live and breathe, ancient-looking fish known as bowfin are guarding genetic secrets
that that can help unravel humanity's evolutionary history and better understand its health.


========================================================================== Michigan State researchers Ingo Braasch and Andrew Thompson are now
decoding some of those secrets. Leading a project that included more
than two dozen researchers spanning three continents, the Spartans have assembled the most complete picture of the bowfin genome to date.

"For the first time, we have what's called a chromosome-level genome
assembly for the bowfin," said Braasch, an assistant professor of
integrative biology in the College of Natural Science. "If you think
of the genome like a book, what we had in the past was like having all
the pages ripped out in pieces. Now, we've put them back in the book."
"And in order," added Thompson, a postdoctoral researcher in Braasch's
lab and the first author of the new research report, published Aug. 30
in the journal Nature Genetics.

This is really important information for a few reasons, the duo said,
and it starts with the bowfin being what Charles Darwin referred to as a "living fossil." The bowfin, or dogfish, looks like an ancient fish.

This doesn't mean that the bowfin hasn't evolved since ancient times,
but it has evolved more slowly than most fishes. This means that the
bowfin has more in common with the last ancestor shared by fish and
humans, hundreds of millions of years ago, than, say, today's zebrafish.



========================================================================== Zebrafish -- which are modern, so-called teleost fishes -- are a notable example because they're widely used by scientists as a model to test
and develop theories about human health. Having more genetic information
about the bowfin helps make the zebrafish a better model.

"A lot of research on human health and disease is done on model organisms,
like mice and zebrafish," Thompson said. "But once you identify important
genes and the elements that regulate those genes in zebrafish, it can
be hard to find their equivalents in humans. It's easier to go from
zebrafish to bowfin to human." For example, one particularly interesting
gene is one that's used in developing the bowfin's gas bladder, an organ
the fish uses to breathe and store air.

Scientists believe that the last common ancestor shared by fish and humans
had air-filled organs like these that were evolutionary predecessors to
human lungs.

In their new study, the Spartan researchers could see that a certain
genetic process in the bowfin's gas bladder development bore striking similarities to what's known about human lung development. A similar
process is also present in the modern teleost fishes, but it's been
obscured by eons of evolution.

"When you looked for the human genetic elements of this organ development
in zebrafish, you couldn't find it because teleost fishes have higher
rates of evolution," Thompson said. "It's there in modern fishes, but
it's hidden from view until you see it in bowfin and gar." The gar is
another air-breathing fish with "living fossil" status that's studied
by Braasch and his team. With both the gar and bowfin genomes, the team
was able to show where these genetic elements linked to gas bladder and
lung formation were hiding out in the modern teleost fishes. The ancient
fish enable researchers to build a better bridge between the established
modern fish model organisms and human biology.



==========================================================================
"You don't want to base that bridge on one species," said Braasch, who
added this finding also strengthens the implications for evolutionary
history. "This is another piece of the puzzle that suggests the common
ancestor of fish and humans had an air-filled organ and used it for
breathing at the water surface, quite similar to what you see in bowfin
and gar." Although these findings have insights that are pertinent to all
of humanity, Spartans might feel a special affinity for the bowfin. For starters, male fish turn their fins and throats a bright shade of green
during spawning season.

Also, famed biologist William Ballard of Dartmouth College studied bowfin development from eggs to larval fish at Michigan State's W.K. Kellogg Biological Station during the 1980s. This was what he called his "Odyssey
of Strange Fish," and Braasch's team now uses his work to guide their
genomic analyses of bowfin development.

Bowfins are native to Michigan. They could be in the Red Cedar
River on MSU's campus now, according to Thompson, but they also
can be quite elusive and, sometimes, very aggressive. This made
collaborations essential for securing specimens. With colleagues at
Nicholls State University in Louisiana, the team caught bowfins for
genome sequencing. Amy McCune, a collaborator and professor at Cornell University, knew where to find bowfin eggs in upstate New York and had a graduate student gifted at securing these unique samples for investigating bowfin development.

The Spartans also had connections at other universities and institutions
with experts in bowfin biology, chromosome evolution and more. All told,
the team included researchers from six states as well as France, Japan
and Switzerland.

Back in East Lansing, graduate students Mauricio Losilla and Olivia Fitch, research technologist Brett Racicot, and Kevin Childs, director of the
MSU Genomics Core facility, also contributed to the study, which comes
with an interesting twist at the end.

Almost all vertebrate creatures that grow paired limbs or fins share a
common gene.

"Humans use it, mice use it. All fishes that have been studied so far use
it," Braasch said. "The nai"ve expectation would be that bowfin do, too."
But that's not what the team found. The bowfin, the "living fossil,"
has evolved a different way of growing its paired fins.

"For whatever reason, it changed its genetic programming. Even
'living fossils' keep evolving. They're not frozen in time," Braasch
said. "It's sort of a cautionary tale that we shouldn't take these
things for granted. You have to look trait by trait, gene by gene
and across many different species to paint the complete picture." ========================================================================== Story Source: Materials provided by Michigan_State_University. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Andrew W. Thompson, M. Brent Hawkins, Elise Parey, Dustin J. Wcisel,
Tatsuya Ota, Kazuhiko Kawasaki, Emily Funk, Mauricio Losilla,
Olivia E.

Fitch, Qiaowei Pan, Romain Feron, Alexandra Louis, Je'ro^me
Montfort, Marine Milhes, Brett L. Racicot, Kevin L. Childs, Quenton
Fontenot, Allyse Ferrara, Solomon R. David, Amy R. McCune, Alex
Dornburg, Jeffrey A. Yoder, Yann Guiguen, Hugues Roest Crollius,
Camille Berthelot, Matthew P. Harris, Ingo Braasch. The bowfin
genome illuminates the developmental evolution of ray-finned
fishes. Nature Genetics, 2021; DOI: 10.1038/ s41588-021-00914-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210830140300.htm

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