Scientists identify gene family key to unlocking vertebrate evolution


Date:
September 16, 2020
Source:
University of Colorado at Boulder
Summary:
New research finds that the traits that make vertebrates distinct
from invertebrates were made possible by the emergence of a new set
of genes 500 million years ago, documenting an important episode
in evolution where new genes played a significant role in the
evolution of novel traits in vertebrates.



FULL STORY ==========================================================================
New University of Colorado Boulder-led research finds that the traits
that make vertebrates distinct from invertebrates were made possible by
the emergence of a new set of genes 500 million years ago, documenting
an important episode in evolution where new genes played a significant
role in the evolution of novel traits in vertebrates.


==========================================================================
The findings, published today in Nature, show that a gene family only
found in vertebrates is critical for forming the head skeleton and other
traits unique to them during embryonic development.

"Every animal essentially has the same basic core set of Lego pieces to
make them. What this paper shows is that vertebrates have a few special
pieces in addition to that, and we identify those special pieces," said
Daniel Medeiros, senior author of the paper and associate professor of
ecology and evolutionary biology.

These special pieces in vertebrates are known as the Endothelin signaling pathway, a set of genes that influence how cells talk to each other. The researchers found this gene family is responsible for allowing neural
crest cells -- cells that develop into unique vertebrate traits like
skeletal parts, pigment cells and our peripheral nervous system --
to proliferate and specialize into different roles throughout the body.

Evolutionary theories have given weight to the role of genome duplication
in the evolution of new traits, and for good reason. When a genome
duplicates, new copies of existing genes can take on new roles in an
organism. But since previous ideas were based mostly on observation,
Medeiros wanted to test if gene duplication could have allowed vertebrates
to become so special, or if the appearance of brand new genes could have
played a role.

Medeiros and his colleagues tested the hypothesis that new gene families
could also give rise to new traits by genetically modifying the larvae
of sea lamprey, a type of jawless fish, through identifying and removing
this specific gene family. If their prediction was correct, removing
it would revert a sea lamprey during its larval development into a more invertebrate-like worm, a close evolutionary ancestor.



==========================================================================
"And we found that by knocking out this new gene family, you can almost
erase most of the key vertebrate traits that make vertebrates special,"
said Medeiros.

While gene duplication is still an important part of the evolutionary
process - - as this new gene family is also duplicated in vertebrates --
they found that duplication was not as critical in giving rise to the
special neural crest cell types that vertebrates evolved as was the
emergence of this new gene family.

This finding is significant in part because it's rare to find clear roles
for genes that are unique to vertebrates, said lead author Tyler Square,
who recently completed his PhD in the Medeiros lab and is now at the
University of California Berkeley.

"We thought that gene duplication was the most important thing. But here,
we found both of those things [new genes and duplications] happening at
once," said Square.

Reverse engineering the first fish Fish were the first vertebrates, from
which all others evolved -- including humans. But there is a gap in the
fossil record right when the first fish were evolving, because they had
little, soft skeletons which were not preserved in the fossil record.



==========================================================================
So how can scientists work out where the first fish came from, and
therefore how all vertebrates came to be? "Rather than looking at
fossils, we use tools like molecular biology and genetics to try to
understand how evolution has happened, kind of like genetic paleontology,"
said Medeiros. "In the deepest molecular genetic terms, we're trying to
reverse engineer how a creature evolves. It's the closest you can get to Jurassic Park." The creature they chose to reverse engineer, however,
might seem a bit monstrous.

"While most people think of a big ugly hurricane of teeth sticking on to
fish and chewing on them, sea lamprey are surprisingly cute when they're
little baby larvae," said Square.

The sea lamprey, a jawless fish, diverged in evolution from other fish
500 million years ago. Because they hold onto several older vertebrate features, this gives the researchers the best snapshot of the early
stage of vertebrate evolution with a living organism today.

"A lamprey and a human are extremely different. But by doing these kinds
of studies, we can know what makes them the same," said Square. "This
is stuff that's really fundamental, not just to mammals and humans, but
to every vertebrate that exists." Square and his colleagues used the gene-editing tool CRISPR during its early days to find out how important
this new gene family is to making vertebrates, well, vertebrates.

"It was the wild west of CRISPR days," said Square. "But we couldn't
have done this whatsoever if it weren't for CRISPR." Not only did
this technology allow the researchers to test hypotheses functionally,
by knocking out genes, but they were also the first team to use CRISPR
in sea lampreys. Previously, this technology had only been used in some vertebrates like mice, frogs and zebrafish.

"And that's a really narrow view of life on the planet," said
Medeiros. "What CRISPR has done is democratized genetic studies across
diverse organisms. It's super powerful for answering evolutionary
questions."

========================================================================== Story Source: Materials provided by
University_of_Colorado_at_Boulder. Original written by Kelsey
Simpkins. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Square, T.A., Jandzik, D., Massey, J.L. et al. Evolution of the
endothelin pathway drove neural crest cell diversification. Nature,
2020 DOI: 10.1038/s41586-020-2720-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200916131041.htm

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