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Discovered Gene Controls Social Eating Behavior - HHMI
is C. elegans and why work on it? - U of Missouri
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Do you eat or need to be around people when youâ€™re stressed?
As this ScienCentral News video reports, scientists are studying the nerve
cells of tiny worms to find out why.
Anxious Worms Stick Together
Humans are social animals and our social interactions and social behaviors
are some of the most important and interesting features of our lives. Scientists
have been trying to understand how genes and nerves can affect our behavior.
Since humans are very complex animals, researchers have often turned to one
of the simpler animals—like the C.
elegans, a nematode, a tiny worm, barely bigger than a comma on this
Bargmann, professor at the University of California San Francisco and
an investigator of the Howard
Hughes Medical Foundation says, “We know that some aspect of behavior
is influenced by genetics and by genetic differences between individuals.
But we donâ€™t know exactly how the genes affect behavior, and what kinds
of genes are involved.” She says the reason scientists study C. elegans
is because they know all of their genes and all of their nerve cells. Therefore
they can study the wormâ€™s brain at a very high level of detail.
Bargmann, Mario de
Bono, and others saw that in the wild these worms exhibited two different
kinds of feeding behaviors: Some were social and others solitary. In an earlier
study they found that the worms were genetically different. Now they wanted
to find out what was making the “social” worms aggregate when
feeding. They associated this behavioral difference to a natural variation
at a single amino acid residue of a neuropeptide receptor called NPR-1. Neuropeptide
receptor is a brain chemical that nerve cells use to communicate with each
other. Worms lacking npr-1 strongly aggregated to feed, indicating that the
presence of npr-1 represses this behavior and made them solitary.
In a study
reported in the journal Nature, Bargmann and colleagues say that in
the social worms they identified a set of genes that are switched on in the
nerve cells that are known to sense stressful situations. The nerve cells,
neurons, seemed to be sending repulsive or distress signals when they
encountered food, and that was promoting the social feeding behavior.
“And so we tried to understand what it was about the food that made them
prefer to aggregate rather than be alone”, says Bargmann. “We
learned that the animals aggregate in response to conditions that they may
find frightening or stressful, and that the food that we feed them actually
alarms some of the animal and this is what causes them to gather into feeding
Further investigation revealed that the wormâ€™s food source, which is
E-coli and many soil bacteria, can kill C. elegans under certain conditions
in the wild.
Bargmann points out that there could be evolutionary advantages for showing
either social or solitary behaviors, depending on the circumstances, and thatâ€™s
probably why both of those different behaviors are present. From an evolutionary
perspective, social behavior in animals is often influenced by environmental
conditions. Animals may gather in the presence of a predator, to protect each
other from toxins, to mate, raise young, or to eat food that may be difficult
But while there are advantages to aggregation, there are also disadvantages.
By coming together in a group they may be more conspicuous to a predator,
they may get less food to eat (since they have to share), or they may be more
susceptible to infectious diseases.
So, Bargmann says, “We think that these behaviors are regulated in the
animal so that different aspects of the behavior will be present depending
on whether it makes more sense for the animal to go it alone…or whether
it makes more sense for them to go it together. So perhaps to our surprise,
the feeding groups [of worms] are not just a positive response to each other,
itâ€™s a positive response that is encouraged by being a little frightened
of the environment in which they find themselves.”
Although the researchers do not want to draw any immediate inferences to human
behavior, they say that a similar gene in mammals is known to influence feeding
“The neuropeptide Y is one of the strongest feeding stimulants known
in mammals, including ourselves,” says Bargmann, adding that it also
“regulates anxiety levels, sensitivity to stressful signals.”
So, is it possible that the differences in human behavior between individuals
may be at the molecular level, just as in the worms? Bargmann says itâ€™s
too soon to tell. Researchers are just starting to tease apart the kinds of
pathways that act in those sorts of human behaviors.
Bargmann's work was supported by Wellcome
Trust, Howard Hughes Medical Institute, and the Medical
Research Council of Great Britain.