The sixth sense of worms
You probably know that we have a sixth sense, named proprioception, which allows us to know where we are in space and helps us "to put one foot in front of the other to walk without looking at your feet." Now researchers at the University of Michigan have found that some worms also have a sixth sense. By studying these worms, they discovered that some neurons could "regulate stretch receptors which tell the body how to move." And as this control of movement seems similar in worms and humans, this discovery could lead to new treatments for people affected with Parkinson's disease.
In a previous news release, "Moving in the 'Sixth Sense'," the University of Michigan gave more details about this phenomenon.
Shawn Xu, Life Sciences Institute research assistant professor and assistant professor of Physiology at UM Medical School, and his colleagues [in his lab] discovered that the "sixth sense" is present in the nematode C. elegans. Because C. elegans is a simple genetic model organism, they were able to dissect in detail how these animals employ proprioception to guide muscle movement.
They identified a critical ion channel protein, TRP (pronounced trip), that acts in the stretch receptor to guide muscle movement. As TRP channel proteins are also found in humans, this suggests that related human proteins may carry the same function in humans. Of equal importance, the worm stretch receptor the Xu team identified is functionally analogous to human muscle spindles and Golgi tendon organs, the two critical types of stretch receptors that regulate muscle movement in humans.
Now let's look at the normal movement of a wild-type C. elegans nematode worm (Credit: Shawn Xu's lab).
And below you can see how "a trp-4 genetically altered mutant C. elegans bends its body abnormally. When the trp channel is turned off, the worm overbends its body." (Credit: Shawn Xu's lab).
Obviously, the second worm looks more agile than the first one. This is even more obvious if you look at these two short videos of a normal worm (1.95 MB) and a genetically altered one (1.97 MB).
This research work has been published by Nature under the name "A C. elegans stretch receptor neuron revealed by a mechanosensitive TRP channel homologue" (Volume 440, Number 7084, Pages 684-687, March 30, 2006). Here are two links to the abstract and to the editor's summary, "Once more with feeling," shown below.
Proprioception, the sense of self, is essential for our daily life. For example, we count on proprioception to 'feel' our body position in space and guide how much to extend our arms and legs. A study of the roundworm C. elegans shows that it uses proprioception to control its body posture and position during locomotion. This requires a single proprioceptor neuron and a mechanosensitive ion channel functioning in this neuron.
Interestingly, this C. elegans neuron is functionally analogous to human muscle spindles and Golgi tendon organs that are important for controlling arm and leg movements. These results suggest that the basic principles of proprioception are evolutionarily conserved between C. elegans and humans, and indicate that C. elegans can be a valuable model organism for studying proprioception and its related human diseases.
And here is the conclusion from Shawn Xu.
"It appears that some of the basic principles underlying sensory regulation of motor activity are evolutionally conserved from worms to human," Xu said. "Thus, C. elegans promises a valuable genetic model for studying proprioception and its related human diseases."
Sources: University of Michigan news release, April 3, 2006 and March 29, 2006; Nature, March 30, 2006; and various web sites
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