Early Onset and Temporo-Spatial Switch of Melanopsin Isoforms Expression in The Developing Chicken Retina

VERRA DM; CONTIN MA; HICKS D; GUIDO ME

INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE

ASSOC RESEARCH VISION OPHTHALMOLOGY INC

Año: 2011 vol. 52 p. 5111 - 5120

0146-0404

Purpose:  Retinal ganglion cells (RGCs) expressing the photopigment melanopsin (Opn4) display intrinsic photosensitivity. Here, we investigated the presence of non-visual phototransduction cascade components in the developing chicken retina and primary RGCs cultures, focusing on the two Opn4 genes, the Xenopus (Opn4x) and the mammalian (Opn4m) orthologs. Methods: Retinas were dissected at different embryonic (E) and postnatal (P) days while primary RGC cultures were obtained at E8 and kept for 1 h to 5 days. Samples were processed for RT-PCR and immunochemistry. Results: Embryonic retinas expressed the master eye gene Pax6, the prospective RGC specification gene Brn3 and components of the non-visual phototransduction cascade like Opn4m and the G protein q (Gq) mRNAs at very early stages (E4-5). By contrast, expression of photoreceptor cell markers (CRX, red-opsin, rhodopsin and á-transducin) was observed from E7-E12. Opn4m protein was visualized in the whole retina as early as E4 and remained elevated from E6 to postnatal days, while Opn4x was weakly detected at E8 and highly expressed after E11. RGC cultures expressed Gq mRNA as well as both Opn4 mRNAs and proteins. Opn4m was restricted exclusively to the GC layer at all ages whereas Opn4x was limited to the forming GC layer and optic nerve at E8, but by E15 its expression was mostly in Prox1 (+) horizontal cells. Conclusions: The early expression onset of non-visual phototransduction molecules could confer premature photosensitivity to RGCs, while appearance of Opn4x expression in horizontal cells suggests the existence of a new type of photosensitive cell in birds.