Grm6 — Glutamate Metabotropic Receptor 6 is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
GRM6 (Glutamate Metabotropic Receptor 6) encodes the metabotropic glutamate receptor 6 (mGluR6), a Group III metabotropic glutamate receptor primarily involved in visual signal transduction.
| Attribute |
Value |
| Gene Symbol |
GRM6 |
| Full Name |
Glutamate Metabotropic Receptor 6 |
| Chromosomal Location |
5q35.3 |
| NCBI Gene ID |
2917 |
| OMIM |
604101 |
| Ensembl ID |
ENSG00000113282 |
| UniProt |
O43524 |
The GRM6 gene encodes mGluR6, an 877 amino acid G protein-coupled receptor.
- UniProt ID: O43524
- Molecular Weight: ~98 kDa
- Subcellular Localization: ON-bipolar cell dendrites in retina
- Protein Family: Class C GPCR, mGluR family
mGluR6 has characteristic Class C GPCR structure:
¶ Extracellular Domain
- Venus flytrap domain (VFT): Large ligand-binding domain with two lobes
- Cysteine-rich domain (CRD): Links VFT to transmembrane domain
¶ Transmembrane Domain
- 7 transmembrane helices: Classic GPCR architecture
- ON bipolar-specific: Critical for visual signal transduction
¶ Intracellular Domain
- C-terminal tail: Contains trafficking signals
- Postsynaptic density: Organizes signaling complexes
mGluR6 is uniquely expressed in retinal ON-bipolar cells:
- Light detection: In darkness, photoreceptors release glutamate
- mGluR6 activation: Glutamate binds mGluR6 on ON-bipolar cells
- G protein signaling: Activates Go protein
- Channel closure: TRPM1 channels close, hyperpolarizing the cell
- Signal transmission: ON bipolar cells remain active in light, OFF in darkness
| Feature |
Description |
| Specificity |
Only ON-bipolar cells express mGluR6 |
| Signal |
mediates ON response to light |
| Contrast |
Critical for detecting light/dark transitions |
| Adaptation |
Involved in light/dark adaptation |
Mutations in GRM6 cause CSNB1A:
- Inheritance: Autosomal recessive
- Symptoms:
- Night blindness from birth
- Reduced visual acuity
- Nystagmus
- Myopia
- Mechanism: Loss of mGluR6 function disrupts ON-bipolar cell signaling
Pathogenic variants:
- Missense mutations (most common)
- Truncating mutations
- Splicing variants
Some studies suggest involvement:
- Visual processing deficits in AD
- mGluR6 expression in visual cortex
- May relate to visual hallucinations
Therapeutic potential:
- Photoreceptor protection strategies
- Gene therapy approaches
- Pharmacological modulation
- Retina: ON-bipolar cells exclusively
- Brain: Very low expression in some regions
- Other tissues: Not expressed
mGluR6 is specifically expressed in:
- ON-bipolar cells
- Rod bipolar cells
- Cone ON-bipolar cells
| Agent |
Mechanism |
Status |
Indication |
| L-AP4 |
mGluR6 agonist |
Research |
Retinal degeneration |
| LY341495 |
mGluR6 antagonist |
Research tool |
- |
| AAV-GRM6 |
Gene therapy |
Preclinical |
CSNB |
- AAV-mediated GRM6 delivery
- CRISPR approaches for specific mutations
- Promising for congenital CSNB
- Blood-retinal barrier limits delivery
- Specificity of targeting
- Preserving proper ON/OFF balance
- GRM6-/- mice show:
- Electroretinogram abnormalities
- Loss of ON responses
- Normal OFF responses
- Night blindness phenotype
- GRM6 mutant mice:
- Recapitulate CSNB phenotype
- Used for therapeutic testing
- Conn PJ, et al. (2009). Pharmacology and functions of metabotropic glutamate receptors. Annu Rev Pharmacol Toxicol.[1]
- Koike C, et al. (2010). mGluR6 in the retinal ON bipolar cells. Vis Neurosci.[2]
- Schluter A, et al. (2019). GRM6 variants and congenital stationary night blindness. Hum Mutat.[3]
- Dhingra A, et al. (2008). The TRPM1 channel in ON-bipolar cells. J Neurophysiol.[4]
- Xu Y, et al. (2012). mGluR6 mutations and retinal disease. Invest Ophthalmol Vis Sci.[5]
The study of Grm6 — Glutamate Metabotropic Receptor 6 has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
[1] Conn PJ, et al. Pharmacology and functions of metabotropic glutamate receptors. Annu Rev Pharmacol Toxicol. 2009;49:291-322.
[2] Koike C, et al. mGluR6 in the retinal ON bipolar cells. Vis Neurosci. 2010;27(3-4):79-87.
[3] Schluter A, et al. GRM6 variants and congenital stationary night blindness. Hum Mutat. 2019;40(11):1915-1926.
[4] Dhingra A, et al. The TRPM1 channel in ON-bipolar cells. J Neurophysiol. 2008;99(6):3072-3082.
[5] Xu Y, et al. mGluR6 mutations and retinal disease. Invest Ophthalmol Vis Sci. 2012;53(12):7569-7578.