To first figure out if the larvae could even sense small temperature differences in the 18 to 24 degree "comfort zone," Montell's team set up a preference test that consisted of a plastic plate where one half of the plate was kept at 18 degrees and the other half at a different temperature, from 19 to 24 degrees. After 15 minutes, they counted the number of larvae on each side of the plate.
"It turns out these larvae can discriminate one degree differencesthey prefer 18 over 19 degrees" says Montell. "The question then was: How do they do this?"
Since TRP channels are known to open in response to changes in temperature, Montell's team then tested flies containing mutations in 12 fruit fly TRP genes to see if any were required for the ability to sense temperature changes within the comfort zone.
Eleven of the 12 TRP mutants still preferred 18 degrees to other temperatures in this range. Only the TRPA1 mutant larvae showed no temperature preference, suggesting to the researchers that only TRPA1 is required for comfort zone temperature sensing.
The known "thermoTRPs" all open directly in response to changes in temperature. TRP proteins also are involved in other types of sensory biology, including vision, explains Montell. But rather than being directly triggered by light, a different light sensor molecule activates the TRP vision protein indirectly. Since TRPA1 is not turned on by changes in temperature in the comfortable range, Montell's team reasoned that perhaps, in this range, TRPA1 might be triggered indirectly through a series of steps similar to those that function in vision.
The team then tested flies with mutations disrupting proteins known to work with TRP proteins required for fly vision and found that they, too, were unable to discern temperature differences in the 18 to 24 C range.
Thus, Montell and co-workers have found a new way that TRP channels function in
|Contact: Maryalice Yakutchik|
Johns Hopkins Medical Institutions