Photoreceptor outer segments

The retina comprises two principal components, the non-neural retinal pigment epithelium and the neural retina. The retinal pigment epithelium is an essential component of the visual system both structurally and functionally. It is important for the turnover and phagocytosis of photoreceptor outer segments, the metabolism of retinoids, the exchange of nutrients between the photoreceptors, and the choroidal blood vessels and the maintenance of an efficient outer blood-retinal barrier. 

Wisniewska, A. and W. K. Subczynski. 2006b. Distribution of macular xanthophylls between domains in model of photoreceptor outer segment membranes. Free Radic. Biol. Med. 4 1257-1265. 

Bailey, KR, Ishida, BY, Duncan, KG, Kane, JP, and Schwartz, DM, 2004. Basal reverse cholesterol transport of retinal pigment epithelium cell digested photoreceptor outer segment lipids. Invest Ophthalmol Vis Sci 45, U721. 

Chen, M, Forrester, JV, and Xu, H, 2007. Synthesis of complement factor H by retinal pigment epithelial cells is down-regulated by oxidized photoreceptor outer segments. Exp Eye Res 84, 635-645. 

Mukherjee, PK, Marcheselli, VL, de Rivero Vaccari, JC, Gordon, WC, Jackson, FE, and Bazan, NG, 2007. Photoreceptor outer segment phagocytosis attenuates oxidative stress-induced apoptosis with concomitant neuroprotectin D1 synthesis. Proc Natl Acad Sci U SA 104, 13158-13163. 

The Carotenoids of Macular Pigment and Bisretinoid Lipofuscin Precursors in Photoreceptor Outer Segments... 

Photoreactive Bisretinoid Compounds in Photoreceptor Outer Segments.357... 

PHOTOREACTIVE BISRETINOID COMPOUNDS IN PHOTORECEPTOR OUTER SEGMENTS... 

FIGURE 16.4 Precursors of RPE cell lipofuscin form in the outer segments of photoreceptor cells. The retina of normal rat (A, B) and the Royal College of Surgeons (RCS) rat (C, D) viewed under the phase contrast (A, C) and the epifluorescence microscopy (B, D). In the normal rat, autofluorescent material accumulates as lipofuscin in RPE cells (arrows). In the RCS, due to a defect in RPE cell phagocytosis, shed outer segment membrane builds up at the photoreceptor-RPE interface the autofluorescence in this debris is attributable to lipofuscin precursors that form in photoreceptor outer segments. 

Liu, J., Itagaki, Y., Ben-Shabat, S., Nakanishi, K., Sparrow, J.R., 2000. The biosynthesis of A2E, a fluorophore of aging retina, involves the formation of the precursor, A2-PE, in the photoreceptor outer segment membrane. J Biol Chem. 275, 29354-29360. 

Sun, H. and Nathans, I. Mechanistic studies of ABCR, the ABC transporter in photoreceptor outer segments responsible for autosomal recessive Stargardt disease. /. Bioenerg. Biomemb. 33 523-530, 2001. 

Figure 14.1 Schematic diagram of the blood-retinal barrier (BRB). The retinal cell layers seen histologically consist of retinal pigment epithelium (RPE) photoreceptor outer segments (POS) outer limiting membrane (OLM) outer nuclear layer (ONL) outer plexiform layer (OPL) inner nuclear layer (INL) inner plexiform layer (IPL) ganglion cell layer (GCL) nerve fiber layer (NFL) inner limiting membrane (ILM).

In such a way we were able to conclude that the illumination of suspensions of photoreceptor outer segments by 450 nm light at 77°K, which was known to result in the rhodopsin— prelumirhodopsin transition (corresponding to 11-cis-retinal— transretinal photoisomerization of chromophore), leads also to the appearance of some reduction centers and to the conformational change of membrane. 

Photoreceptor outer segment layer Retina pigment epithelium layer Bruch s membrane Choroid layer... 

Christiansen, J.R., Kolandaivelu, S., Bergo, M.O., and Ramamurthy, V. (2011). RAS-converting enzyme 1-mediated endoproteolysis is required for trafficking of rod phosphodiesterase 6 to photoreceptor outer segments. Proc Nad Acad Sci USA 108 8862-8866. 

Recent proteomic analysis indicated that the cilia of mammalian photoreceptor cells are significantly more complex than other eukaryotic cilium (Liu et al. 2006). Over 1200 different polypeptides have been identified by the quantitative analysis of the proteome of photoreceptor outer segment compared with the proteome of the axoneme/ciliary fraction of mouse photoreceptor cells. This data set contains all previously identified protein components of the photoreceptor cilium (e.g. Schmitt and Wolfrum 2001). An understanding how the identified proteins function in their native environment of the diverse compartments of the photoreceptor cilia will require increased knowledge of their molecular interaction and networking. Insights into the organization and composition of diverse protein complexes may also provide novel information on how functional modules of the cell, recently proposed by Hofmann et al. 2006, are connected. 

---