Biologists zero in on cells' environmental sensing mechanism

Date:
July 28, 2020
Source:
University of Massachusetts Amherst
Summary:
Evolutionary and developmental biologists report that they have
identified a molecular mechanism that allows an organism to change
the way it looks depending on the environment it is exposed to,
a process known as phenotypic plasticity.



FULL STORY ========================================================================== Evolutionary and developmental biologist Craig Albertson and colleagues at
the University of Massachusetts Amherst report that they have identified
a molecular mechanism that allows an organism to change the way it
looks depending on the environment it is exposed to, a process known as phenotypic plasticity.


==========================================================================
In addition to lead investigators Albertson and Rolf Karlstrom, the
team includes recently graduated doctoral students Dina Navon and Ira
Male, current Ph.D. candidate Emily Tetrault and undergraduate Benjamin Aaronson. Their paper appears now in Proceedings of the National Academy
of Sciences.

Albertson explains that the project stems from a desire to better
understand how genes and the environment interact to direct anatomical
shape. "We know that our features are determined by genes, but we also
know that many physical features are shaped by the environment as well. In identical twins, for example, if one becomes a long-distance runner and
the other a body builder, they are going to end up with very different physiques. The skeleton is especially sensitive to such environmental
inputs." Albertson works with a system -- cichlid fishes -- known
throughout the scientific world as champions of phenotypic plasticity
that can alter, in a single season, jawbone hardness or shape to match
feeding conditions. They are also well known for their rapid evolution
and diversity in jaw shapes, which has enabled cichlids to adapt to many different food sources, including algae, plankton, fish, snails and even
the scales of other fishes.

Albertson has spent much of the past two decades trying to reveal
the genetic differences that underlie differences in jaw shape
between species. Now he and colleagues identify the well-studied chemical/molecular system known as the Hedgehog (Hh) signaling pathway as
an important player. More recently he explored whether the same pathway
might also contribute to differences in jaw shape that arise within
species through phenotypic plasticity.

An important clue came as Albertson learned more about how this molecular pathway works. He explains, "There is a well-known mechano-sensor on
most cells, including those that make the skeleton, called the primary
cilium. Cells that lack this organelle are unable to sense or respond
to environmental input, including mechanical load. It turns out that
several key protein components of the Hedgehog pathway are physically associated with this structure, making it an obvious candidate for an environmentally sensitive signal." In the current study, the research
team first showed that plasticity in the rate of bone deposition in
cichlids forced to feed using different foraging modes was associated
with different Hh levels. Greater levels of the signal were detected
in fish from the environment where more bone was laid down and vice
versa. To really nail the question, Albertson teamed up with Karlstrom,
who had previously developed sophisticated tools to study Hh signaling
in zebrafish.

He explains, "Rolf has a bunch of really slick transgenic systems for manipulating that molecular signal in real time. It is sort of like a
volume knob on your stereo -- you can turn it up or turn it down, and then
see how it influences your trait of interest." In this case, they wanted
to see whether Hh levels influenced plasticity in bone deposition rates.

They found that unmanipulated zebrafish deposited different amounts of
bone in different foraging environments. When Hh levels were reduced,
these differences went away, but when Hh levels were increased,
differences in bone deposition rates were dramatically increased.

Albertson, explains, "Bone cells in these fish are innately sensitive
to different mechanical environments. But we were able to play with
this system using a single molecular switch -- you turn up the Hh
signal and the cells become more sensitive to the environment, or
you turn the molecular sensor down and the cells become almost deaf
to the environment." "That the same molecular machinery underlies
both the evolutionary divergence and plasticity of the jaw is notable," Albertson explains. "It is consistent with long-held theory that suggests short-term plasticity might bias the direction of long-term evolution,
which explains why evolution can be predictable in lineages that have repeatedly evolved to similar habitats." Albertson adds, "The Hh signal
has also been shown to regulate plasticity in beetle horns, so there may
be something special that positions it to be an environmental sensor
across tissues and animals." Such intriguing questions will be the
topic for future investigations, the authors add.


========================================================================== Story Source: Materials provided by
University_of_Massachusetts_Amherst. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Dina Navon, Ira Male, Emily R. Tetrault, Benjamin Aaronson, Rolf O.

Karlstrom, R. Craig Albertson. Hedgehog signaling is
necessary and sufficient to mediate craniofacial plasticity in
teleosts. Proceedings of the National Academy of Sciences, 2020;
201921856 DOI: 10.1073/ pnas.1921856117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200728130826.htm

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