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A small number of mammalian retinal ganglion cells act as photoreceptors for regulating certain non-image forming photoresponses. These intrinsically photosensitive retinal ganglion cells express the putative photopigment melanopsin. Ablation of the melanopsin gene renders these cells insensitive to light; however, the precise role of melanopsin in supporting cellular photosensitivity is unconfirmed. Here we show that heterologous expression of human melanopsin in a mouse paraneuronal cell line (Neuro-2a) is sufficient to render these cells photoreceptive. Under such conditions, melanopsin acts as a sensory photopigment, coupled to a native ion channel via a G-protein signalling cascade, to drive physiological light detection. The melanopsin photoresponse relies on the presence of cis-isoforms of retinaldehyde and is selectively sensitive to short-wavelength light. We also present evidence to show that melanopsin functions as a bistable pigment in this system, having an intrinsic photoisomerase regeneration function that is chromatically shifted to longer wavelengths.

Original publication

DOI

10.1038/nature03344

Type

Journal article

Journal

Nature

Publication Date

17/02/2005

Volume

433

Pages

741 - 745

Keywords

NASA Discipline Space Human Factors, Non-NASA Center, Animals, Calcium Signaling, Cell Line, Cyclic GMP, Gene Expression, Heterotrimeric GTP-Binding Proteins, Humans, Light, Light Signal Transduction, Mice, Neurons, Protein Isoforms, Retinaldehyde, Rod Opsins