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Katelyn Noronha, Jasmine Ashley Lucas, Tiffany M Schmidt; Melanopsin expression is dynamically regulated during retinal development. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1746.
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© ARVO (1962-2015); The Authors (2016-present)
In addition to rod and cone photoreceptors of the outer retina, intrinsically photosensitive retinal ganglion cells (ipRGCs) constitute a third class of inner retinal photoreceptors that play roles in both image and non-image forming vision. ipRGCs express melanopsin, a photopigment that renders them intrinsically photosensitive. Each of the five ipRGC subtypes (M1 to M5) express different levels of melanopsin in adult retinas, with M1 ipRGCs expressing the most and M4 and M5 ipRGCs expressing the least. Additionally, M1 ipRGCs have been found to express two isoforms (Opn4S and Opn4L) of the melanopsin protein, while all other subtypes express only one (Opn4L). However, how ipRGCs achieve regulation of both melanopsin levels and melanopsin isoforms is unknown. We examined melanopsin expression levels in ipRGC subtypes across development to begin understand melanopsin regulation.
We assessed ipRGC number in mouse lines where different complements of the ipRGC subtypes can be immunolabeled in adulthood (Opn4Cre, Opn4-GFP, and Opn4LacZ). We then counted the total number of ipRGCs in the retina at postnatal day 2, 4, 6, 8, 14, and during adulthood. We also further examined melanopsin labeling patterns of the M4 subtype in various regions of the retina during development. We used quantitative real-time PCR to detect changes in melanopsin expression and melanopsin isoform expression in the retina during early postnatal development and adulthood.
Unexpectedly, we found that M4 ipRGCs express higher levels of melanopsin in early postnatal development than in adulthood. Our qPCR results indicate that total melanopsin RNA levels, as well as melasnopsin isoform RNA levels, also fluctuate across development, before eventually settling at adult levels.
Our data indicate that ipRGC subtypes differentially and dynamically regulate melanopsin expression. Further investigation will examine the relative melanopsin and melanopsin isoform expression within the different subtypes of ipRGCs across development.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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