Purchase this article with an account.
Ya-Chu Hsu, Jen-Zen Chuang, Roland Thuenauer, Ching-Kang Jason Chen, Yu-Ting Yan, Ching-Hwa Sung; Endosome-dependent Rhodopsin trafficking for outer segment renewal. Invest. Ophthalmol. Vis. Sci. 2016;57(12):574.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The outer segment (OS) of rod photoreceptors undergoes dynamic renewal on a daily basis. However, the mechanism behind this process remains to be fully understood. SARA, a Rhodopsin-binding protein, is an early endosome protein and promotes tethering and fusion of Rhodopsin vesicles during disc biogenesis. We test the hypothesis that endosomes regulated by SARA as well as GTPase Dynamin is involved in protein transport during OS renewal.
Reversible aggregation-based synchronization of Rhodopsin reporter (FM4-Rhodopsin-GFP) was transfected into Madin-Darby canine kidney (MDCK) cells and the biosynthetic pathway of Rhodopsin was traced. Dominant negative (DN) reagents of Rab11 and Dynamin were used to perturb the functions of recycling endosomes and vesicle fission events. The effects on Rhodopsin surface delivery were imaged and compared to those transfected with wildtype agents. Cre-mediated inducible expression system was employed to pulse-express wildtype or DN mutants in matured rods. Rhodopsin reporters were coexpressed to delineate the effect on Rhodopsin’s OS delivery. Rab11 expression was examined by immunolabeling in SARA-knockdown cells and Rod-specific SARA knockout retina sections. Transmission electron microscopy (EM) and focused ion beam scanning EM were employed to perform ultrastructural analyses.
FM4-Rhodopsin-GFP targeted to the apical surface in polarized MDCK. Rhodopsin was traced to the Rab11+ compartments prior to arriving at the apical surface. Expression of Rab11DN or Dynamin greatly reduced the surface delivery of Rhodopsin. In vivo short-pulsed expression of Rab11DN caused Rhodopsin to mislocalize. Perturbing Dynamin functions also caused Rhodopsin to mislocalize, and we observed enlarged membrane profiles and vesicle accumulation in the inner segment. Finally, we found that rods lacking SARA had significant reduction of Rab11. SARA knockout rods had smaller OS diameters and aberrant vesicles in the OS. The structural defects were accompanied by mislocalization of Rhodopsin.
Our data support the hypothesis that endosomes are an integral part of the Rhodopsin transport pathway. Endosomes coupled with the fission activities of Dynamin are a source of OS-destined vesicles. Sara plays a critical role in maintaining the integrity of endosomes vital for protein trafficking and disc morphogenesis.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
This PDF is available to Subscribers Only