Circadian and phototransduction components are present in chicken retinal ganglion cells
Verra DM1, Contín MA1, Guido ME1
1CIQUIBIC (CONICET) ?Dept. of Biological Chemistry, School of Chemical Sciences, National University of Córdoba- Córdoba, Argentina;
Within the vertebrate retina, a small subset of retinal ganglion cells (RGCs) has been shown to be intrinsically photosensitive (?ipRGC?, Berson et al., 2002). Mammals express only one isoform of the photopigment melanopsin (M isoform, Opn4M)(Provencio et al., 2000) , while non-mammalian vertebrates such as the chicken express Opn4m and a second isoform, Opn4x (Bellingham et al., 2006; Tomonari et al., 2005). Both isoforms are orthologs of an ancient invertebrate opsin, present in rhabdomeric photoreceptors (RP). Both ipRGCs and RP also express specification and differentiation factors such as Pax 6, Athonal, Brn 3 and Bar H. In addition, we have demonstrated that primary cultures of immunopurified embryonic RGCs at embryo stage 8 (E8) express Pax6, Brn3 and the Gq protein mRNAs while the phototransduction cascade operating in these cells is very similar to that observed in the invertebrate photoreceptors (Contín et al., 2006, The FASEB Journal).
We use immunopurified chicken RGCs as a suitable model for the study of non-visual phototransduction, and its direct involvement in the setting of the central pacemakers located in the brain. RGCs are obtained by immunopanning with the Thy-1 antibody at embryo stage 8 (E8), at which they are postmitotic and mostly mature. We described that chicken RGCs produce the hormone melatonin on a circadian basis (Garbarino et al, JBC 2004), but with a diurnal peak in antiphase to the nocturnal maximum observed in photoreceptors. Some RGCs in the cultures are photoresponsive, showing a suppressive effect of a light pulse on 3H-melatonin levels as compared to cells kept in the dark (Contín et al., FASEB J 2006).
Here, we describe the transcriptional and protein profile of different elements involved in visual and non-visual phototransduction and retinoid regeneration in the whole retina during the eye development of chicken embryos as well as in RGC cultures at E8. Also, we show preliminary results about the temporal and light regulation of Opn4x and Opn4m expression in DD.
