Working on the clock machinery. Non visual photoreception in chicken retinal ganglion cells.

VERRA DANIELA MARIANA; CONTIN MARIA ANA; GUIDO MARIO EDUARDO

Los Cocos- Cordoba Argentina

Workshop; VIII Latin American symposium of chronobiology; 2005

Working on the clock machinery. Non visual photoperception in Chicken Retinal Ganglion Cells? Verra, DM; Contín MA; Guido ME. Dpto. Química. Biológica-CIQUIBIC- Fac. Cs. Qcas.- Universidad Nacional de Córdoba- mail: dverra@mail.fcq.unc.edu.ar             It is known, that blind animals lacking functional rods and cones, perceive light (non visual photoperception), that synchronizes its physiology and behaviour  (reviewed in Guido et al, 2002). The retina is also necessary for synchronization in vertebrates that involves other kind of photoreceptors/photopigments. Recent studies have demonstrated the presence of new photopigments (cryptochromes, melanopsin and others) in mammalian retinal ganglion cells (RGCs) (Miyamoto and Sancar, 1998; Provencio et al, 2000) with an intrinsic response to light.           Observations from our laboratory indicate that chicken RGCs at embryonic day 8 (E8), synthesize melatonin with a circadian pattern (Garbarino et al., 2004) that is regulated by light (Contín et al., unpublished results). These findings demonstrate that there is a phototransduction cascade involved, necessarily started by a photopigment. Our goals were to investigate the expression of diverse mRNAs involved in phototransduction mechanisms and melatonin synthesis: a) the classical photopigments rhodopsin and red opsin, b) the non-visual photopigments melanopsin and cryptochromes, and c) hydroxyindole O-methyltransferase (HIOMT), the enzyme in the final step of melatonin synthesis. We investigated the expression of the mentioned mRNAs in RGC cultures from chicken embryonic retinas at E8 by RT-PCR. First results have shown high levels of a rhodopsin-like transcript, and a differential expression of melanopsin, cry 2 and HIOMT. Melanopsin mRNA is detectable at E8, increasing up to the 5th day in culture, and decreasing by 7 days in the same conditions. These results suggest the idea that in early embryonic stages of the chicken retina, oscillators and photopigments may converge all together in the same RGC population as seen in the expression of different photopigments and melatonin biosynthetic enzymes.