The first step of our vision takes place in the retina where light is captured in the outer segment of photoreceptor cells. This light-sensing organelle is unique in that it is a modified primary cilium that is concentrated with proteins involved in visual signal transduction. Synthesis of these proteins occurs in the cell soma, followed by their delivery to the outer segment by discrete intracellular trafficking mechanisms. The visual pigment rhodopsin is the most abundant protein of the outer segment membranes and its targeting from the ER/Golgi to the outer segments is mediated by a small guanine nucleotide-binding protein Arf4. Though intracellular targeting and trafficking of rhodopsin is understood better than any other photoreceptor-specific protein, many mechanistic aspects remain unclear including the molecular event activating Arf4 to initiate rhodopsin sorting. As other guanine nucleotide-binding proteins, Arf4 is expected to be activated upon GDP/GTP exchange. Thus the first aim of my proposal is to determine the guanine nucleotide exchange factor that fulfills this function in photoreceptors.
My second aim i s to identify whether Arf4 is uniquely required for rhodopsin sorting and whether other proteins rely on Arf4 for targeting to the outer segments. I will also explore the hypothesis that Arf4 may be engaged in protein sorting to ciliary organelles in other cells. This project has broad implication for our general understanding of pathobiological processes underlying cases of inherited retinal degenerations, which are caused by mutations affecting protein sorting to the outer segment of photoreceptors.

Public Health Relevance

Retinal degenerative diseases leading to blindness afflict human populations worldwide. The most severe cases of inherited retinal degeneration are caused by mutations that affect trafficking of the light receptor rhodopsin to photoreceptor outer segments. In this application we propose to study protein trafficking to the outer segments, which will increase our understanding of the molecular foundation of inherited retinal diseases and provide possibilities for future therapeutic treatments.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
5F32EY022508-02
Application #
8456241
Study Section
Special Emphasis Panel (ZRG1-F05-P (20))
Program Officer
Agarwal, Neeraj
Project Start
2012-04-01
Project End
2015-03-31
Budget Start
2013-04-01
Budget End
2014-03-31
Support Year
2
Fiscal Year
2013
Total Cost
$52,190
Indirect Cost
Name
Duke University
Department
Ophthalmology
Type
Schools of Medicine
DUNS #
044387793
City
Durham
State
NC
Country
United States
Zip Code
27705
Pearring, Jillian N; Lieu, Eric C; Winter, Joan R et al. (2014) R9AP targeting to rod outer segments is independent of rhodopsin and is guided by the SNARE homology domain. Mol Biol Cell 25:2644-9