Rhodopsin, a pigment of the retina that is responsible for perception of light is also involved in temperature sensation.
The work emerged from a collaboration between the laboratory of Andrew Chess, M.D., Professor in the Departments of Neuroscience, Developmental and Regenerative Biology and Genetics and Genomic Sciences at Mount Sinai, and the laboratory of Craig Montell, Ph.D., Professor of Biological Chemistry at Johns Hopkins School of Medicine. Their paper, titled "Function of rhodopsin in temperature discrimination in Drosophila," is published in the March 11 edition of Science
The research focused on rhodopsin in Drosophila larvae, commonly known as fruit flies. The temperature-detection function of rhodopsin allows the Drosophila larvae to move to their preferred temperature of 18 degrees Celsius (64.4 degrees Fahrenheit). This ability depends on a thermosensory signaling pathway that includes a heterotrimeric guanine nucleotide-binding protein, or G-protein.
"It is very surprising that rhodopsin has a role in temperature sensation, as it was thought to be completely devoted to its well-known role as a light sensor," said Dr. Chess, Mount Sinai School of Medicine. "This function of rhodopsin allows temperature discrimination in the comfortable range."
This new role for rhodopsin emerged from studies of the process that results in the activation of a temperature-sensor protein known as a TRPA1, which Dr. Montell's group has been studying.
The researchers released about 75 larvae onto a plate with two temperature zones. Half of the plate was kept at 18 degrees Celsius and the other half ranged from 14 to 32 degrees Celsius. After ten minutes, the larvae lacking rhodopsin could not discriminate temperatures in comfortable range, just like the larvae lacking TRPA1.
The mouse gene melanopsin is the closest mouse gene to Drosophila rhodopsin
. Mouse melanopsin can functionally replace the thermosensory function of Drosophila rhodopsin
The Drosophila larva has peripheral neurons that mediate thermosensation. These neurons are distinct from neurons that allow detection of light. Since the rhodopsins generally have low susceptibility to thermal activation, there is likely a distinct, yet-to-be-discovered, protein that allows thermal activation of rhodopsin.