Retinal Muller glial cells in the developing retina of birds express the non-visual opsin Opn3 and respond to blue light

GUIDO, M.E.; RIOS, M.N.; MARCHESE, N.A.

Barcelona

Congreso; 17th Congress of the International Union of Photobiology and 18th Congress of the European Society for Photobiology; 2019

International Union of Photobiology

The retina of birds contains different types of photoreceptors involved in image and non-image forming activities: the visual photoreceptor cells (cones and rods) and the melanopsin-expressing cells (intrinsically photoresponsive retinal ganglion cells ?ipRGCs- and horizontal cells). In addition, the nonvisual opsins Opn3 (encephalopsin/panaopsin) and Opn5 (neuropsin) have been found to be expressed in the vertebrate inner retina, responding to blue (BL) and UV light, respectively. Diverse retinal processes are regulated by light, among them is the functioning and adjusting of the retinal circadian clock that temporally controls retinal physiology. Here we evaluated the expression, localization and possible light regulation of Opn3 and Opn5 in the developing retina at different embryonic days (E) in the whole chick retina as well as in primary cultures of Müller glial cell (MC), by PCR, immunochemistry and fluorescence calcium imaging. Opn3 and Opn5 mRNAs and proteins appeared as early as E7-10, in the developing RGC layer and glial cells that extend throughout the forming nuclear layer. At E15, and later on ?up to post-natal day 10- , a significant increase in both opsins? levels was observed in inner retinal cells, together with expression of the glial marker glutamine synthetase (GS). Opn3 and Opn5 were found to be expressed in primary neuronal and MC cultures prepared as early as at E8 and kept for 2 weeks. Significant but opposite effects of BL exposure on Opn3 expression levels and subcellular localization were observed in neuronal and MC cultures: BL substantially affected Opn3 expression in RGCs, promoting a decrease in protein levels and a change in subcellular localization away from processes, whereas in MCs, BL significantly increased its expression and modified its nuclear location. More importantly, a subpopulation of MCs responded to brief BL pulses by increasing intracellular Ca2+ levels. In addition, these cells also significantly changed their cellular area in response to BL. Taken together; our results show that these two opsins are expressed in inner retinal cells at early developmental stage, in both neurons and MCs of the chicken retina, with protein levels strongly regulated by light at early stages in which no-sign of vision may occur. The novel photic response observed in MCs allows us to infer that an important role is likely played by these cells in retinal physiology during the day or after light exposure.