Illumination of the Melanopsin Signaling Pathway

Expression of melanopsin in Xenopus oocytes leads to light-dependent activation of membrane currents through the Galpha(q)/Galpha(11) G protein pathway.

• Melanopsin plays a key role in nonvisual photic responses in mammals, such as sleep regulation and pupil constriction.
• The action spectrum of melanopsin-expressing retinal ganglion cells aligns with behavioral responses to light in mice without rods and cones.
• Coexpression with arrestins allows melanopsin to use all-trans-retinaldehyde, indicating it may act as a bireactive opsin.
• Melanopsin activates the cation channel TRPC3, suggesting a signaling mechanism similar to invertebrate opsins rather than traditional vertebrate opsins.

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