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Satyabrata Sinha, Marycharmain Belcastro, Seongjin Seo, Maxim Sokolov; The Essential Role of CCT in Outer Segment Morphogenesis. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1227.
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© ARVO (1962-2015); The Authors (2016-present)
Previously, we demonstrated that the development of the rod outer segment, a sensory cilia responsible for light detection, is crucially dependent on the normal function of the cytosolic chaperonin containing T-complex protein 1, CCT. Our goal here was to identify the underlying molecular mechanism for such a phenotype.
The activity of CCT in photoreceptors and cell culture was suppressed by overexpressing a short splice isoform of phosducin-like protein, PhLPs. Cellular morphology was analyzed by light microscopy and electron microscopy. Protein-protein interactions of CCT were determined using an immunoprecipitation assay coupled to LC/MS/MS. Protein expression levels were studied by immunofluorescence and Western blotting.
We identified several proteins that were severely down-regulated in response to CCT suppression and involved in outer segment morphogenesis. Those included Bardet-Biedl Syndrome proteins 2, 5 and 7, essential subunits of the cilia BBSome complex, and oxysterol-binding protein 2 (OSPB2), implicated in non-vesicular lipid trafficking. Interestingly, the reduction of rhodopsin and peripherin appeared to be secondary event, as both proteins were still targeted to the outer segment remnants.
Our data provide evidence that CCT may potentially be involved in posttranslational processing of BBS 2, BBS5, BBS7, and OSPB2, which thus underlines its crucial importance in outer segment morphogenesis.
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