An Invertebrate-like Phototransduction Cascade Mediates Light Detection in the Chicken Retinal Ganglion Cells

CONTIN MA; VERRA DM; GUIDO ME

FASEB JOURNAL

FEDERATION AMER SOC EXP BIOL

Año: 2006 vol. 20 p. 2648 - 2650

0892-6638

Pre-bilaterian animals perceived ambient light through non-visual rhabdomeric photoreceptors (RPs), which evolved as support of the chordate visual system. In vertebrates, the identity of non-visual photoreceptors and the phototransduction cascade involved in non-image forming tasks remain uncertain. We investigated whether chicken retinal ganglion cells (RGCs) could be non-visual photoreceptors, and the nature of the photo-cascade involved. We found that primary cultures of chicken embryonic RGCs express such RP markers as transcription factors Pax6 and Brn3, photopigment melanopsin, and G-protein q, but not markers for ciliary photoreceptors (a-transducin and Crx). To investigate the photoreceptive capability of RGCs, we assessed the direct effect of light on 3H-melatonin synthesis in RGC cultures synchronized to 12:12 h light dark cycles. In constant dark, RGCs displayed a daily variation in 3H-melatonin levels peaking at subjective day, which was significantly inhibited by light. This light effect was further increased by the chromophore all-trans retinal and suppressed by specific inhibitors of the invertebrate photo-cascade involving phosphoinositide hydrolysis (100 µM neomycin; 5 µM U73122) and Ca2+ mobilization (10 mM BAPTA; 1 mM lanthanum). The results demonstrate that chicken RGCs are intrinsically photosensitive RPs operating via an invertebrate-like phototransduction cascade, which may be responsible for early detection of light before vision occurs.