melanopsinencoded

Melanopsin is a photopigment found in specialized retinal ganglion cells known as intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells play a crucial role in regulating various physiological and behavioral responses to light, distinct from traditional vision mediated by rods and cones. The gene encoding melanopsin is called *OPN4* (opn4, also referred to as *Gq melanopsin* or *melanopsin-encoded gene*), located on chromosome 4 in humans.

Discovered in the late 1990s, melanopsin was initially identified in the skin of fish and amphibians, where it functions in circadian rhythm regulation and color vision. Its presence in mammalian retinas was later confirmed, revealing its role in non-image-forming vision processes such as pupil constriction, circadian entrainment, and suppression of melatonin secretion. Unlike rod and cone photoreceptors, ipRGCs containing melanopsin are directly sensitive to light wavelengths between 446 and 490 nanometers, with peak sensitivity around 480 nm (blue-green light).

The melanopsin protein belongs to the G protein-coupled receptor (GPCR) family and activates the Gq signaling pathway upon light exposure. This triggers intracellular cascades that modulate neuronal activity, influencing both direct light responses and indirect feedback to other retinal cells. Mutations in the *OPN4* gene have been linked to rare cases of congenital stationary night blindness and altered circadian rhythms, though its functional impact varies depending on the specific mutation.

Research on melanopsin continues to expand, particularly in understanding its role in sleep disorders, mood regulation, and potential therapeutic applications for conditions like non-24-hour sleep-wake disorder. Studies also explore its implications in jet lag adaptation and the effects of artificial lighting on human health.