TRPM1

The protein encoded by this gene is a member of the transient receptor potential (TRP) family of non-selective cation channels. It is expressed in the retina, in a subset of bipolar cells termed ON bipolar cells.^[8][9] These cells form synapses with either rods or cones, collecting signals from them. In the dark, the signal arrives in the form of the neurotransmitter glutamate, which is detected by a G protein-coupled receptor (GPCR) signal transduction cascade. Detection of glutamate by the GPCR Metabotropic glutamate receptor 6 results in closing of the TRPM1 channel. At the onset of light, glutamate release is halted and mGluR6 is deactivated; this results in opening of the TRPM1 channel, influx of sodium and calcium, and depolarization of the bipolar cell.^[10][11]

In addition to the retina, TRPM1 is also expressed in melanocytes, which are melanin-producing cells in the skin. The expression of TRPM1 is inversely correlated with melanoma aggressiveness, suggesting that it might suppress melanoma metastasis.^[12] However, subsequent work showed that a microRNA located in an intron of the TRPM1 gene, rather than the TRPM1 protein itself, is responsible for the tumor suppressor function.^[13][14] The expression of both TRPM1 and the microRNA are regulated by the Microphthalmia-associated transcription factor.^{[15][16][17][13]}

Mutations in TRPM1 are associated with congenital stationary night blindness in humans ^{[18][19][20][21]} and coat spotting patterns in Appaloosa horses.^[22]

• TRPM