Parietal-Eye Phototransduction Components and Their Potential Evolutionary Implications.

PHOTORECEPTORS; PHOTOBIOLOGY; BLUE light; OPTICAL polarization; OPTICS; CELLS; GENETIC transduction; MICROBIAL genetics; GENE fusion

The parietal-eye photoreceptor is unique because it has two antagonistic light signaling pathways in the same cell — a hyperpolarizing pathway maximally sensitive to blue light and a depolarizing pathway maximally sensitive to green light. Here, we report the molecular components of these two pathways. We found two opsins in the same cell: the blue-sensitive pinopsin and a previously unidentified green-sensitive opsin, which we name parietopsin. Signaling components included gustducin — α and Gα[sub o], but not rod or cone transducin-α. Single-cell recordings demonstrated that G[sub o] mediates the depolarizing response. Gustducin-α resembles transducin-α functionally and likely mediates the hyperpolarizing response. The parietopsin-G[sub o] signaling pair provides clues about how rod and cone phototransduction might have evolved. [ABSTRACT FROM AUTHOR]

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