Retinal Protein Expression Under the Control of Light in C57bl6/j Mice and Mice Lacking Photosensitive Cells

Abstract

Purpose: : To study the mechanisms that regulate the expression of specific retinal proteins along the circadian cycle in the mouse retina. In the mammals, circadian rhythms are synchronized to light-dark cycles via a photic input from the eyes. For many years, rods and cones have been regarded as the only photoreceptors present in the eye, and much of the work investigating circadian responses focused solely on these cells. It is now clear that a third class of photoreceptor exists in the mammalian eye: the intrinsically photosensitive retinal ganglion cells (ipRGCs). These cells are characterised by the expression of the melanopsin photopigment (Opn4) and they are known to regulate circadian entrainment and other non-visual response to light.

Methods: : By using Western blotting of plasma membrane and cytoplasmic fractions from mouse retinas collected at different circadian times (ZT0, ZT6, ZT12 and ZT18), we have investigated the levels of expression, localisation and cellular compartmentalisation of retinal proteins such as PKC, Opn4 and NKCC1 in mice containing all photoreceptors (C57Bl6/J), mice lacking rods and cones (Rd10) and mice lacking ipRGCs (Opn4 -/-). Furthermore, we have tested if the differential protein expression under circadian cycles is also detectable by the use of immunocytochemical techniques.

Results: : The use of different mouse models allowed us to investigate the contribution of different classes of photoreceptors in regulating the circadian expression of a series of proteins such as PKC. We have observed that light induces the activation of PKC and its transport to the membrane compartment and that this effect is both mediated by classical photoreceptors and ipRGCs.

Conclusions: : ipRGCs as well as classical photoreceptors mediate chages in retinal protein expression along the cyrcadian cycle.

Keywords: circadian rhythms • protein modifications-post translational • immunohistochemistry