[evol-psych] Worm Shows Link Between Mutation And Behavior Change
- January 4, 2000
Worm Shows Link Between Mutation And Behavior Change
A tiny transparent worm has enabled the first complete description of the
biochemical steps leading from a genetic mutation to a change in behavior,
UT Southwestern Medical Center at Dallas investigators have reported.
The understanding of the connection between genes and behavior at the
molecular level is a major goal of neurobiology.
"A question we want to answer in looking at the human genome is what
controls behavior," said Dr. Leon Avery, associate professor of molecular
biology at UT Southwestern and senior author of the paper. "I believe a lot
of the genetics of human behavior will be understandable in molecular terms
through a change in a single ion channel or single receptor molecule."
The report appeared in the December 24th issue of Science.
The researchers studied a worm called a c. elegans that had a mutation that
affected its feeding behavior. They showed that the mutation in the gene
exp-2 caused an abnormality in a potassium channel so that it remained open
rather than opening and closing normally. This alteration prevented opening
of the pharynx, the muscle used to eat.
The opening of the potassium channel, called EXP-2, causes muscle
relaxation. Normally the muscle relaxes a fifth of a second after
contraction of the muscle. In the mutant worms, it relaxed in a 20th of a
second after the contraction. This meant the muscle never contracted or
opened all the way. The worms could not eat much because they could not
take in adequate food.
"A good way to imagine this is that the pharyngeal muscle is like a pump,
pumping food into the worm," Avery said. "It works very much like a human
heart. If a heart pumps too fast, it can't really pump any blood before it
starts to relax again."
Because the scientists were able to describe the biophysical,
electrophysiological and behavioral effects of this mutation, they now know
every step in the causal chain linking a mutation to altered feeding
behavior in c. elegans. The researchers believe that studying such changes
in molecules eventually may answer behavioral questions right down to why
some people are cheerful and others are grumpy.
The scientists also concluded from studying the worms' EXP-2 channel, which
is related to the human potassium channel HERG, that these similarly
functioning channels, although different in structure and sequence,
apparently evolved to fill the same needs in different animals.
The researchers now will try to determine if modifying the behavior of the
EXP-2 channel also changes the worms' feeding behavior.
The lead author of the study, Dr. M. Wayne Davis, recently earned his
doctorate at UT Southwestern and is now at the University of Utah. Dr.
Richard Fleischhauer, postdoctoral fellow, and Dr. Rolf Joho, associate
professor of cell biology, both in the UT Southwestern Center for Basic
Neuroscience, and Dr. Joseph Dent, assistant professor of biology at McGill
University, Montreal, collaborated on the study.
National Institutes of Health grants supported this research. - By Susan A.