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MS Eckmiller, AF Wright, F Manson; Colocalization of RPGR, RPGRIP, and Microtubules in Different Cytoskeletal Systems in the Outer Segments of Rods and Cones . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3739.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To examine the distribution of two proteins encoded by genes implicated in human retinal degenerations, Retinitis pigmentosa GTPase regulator (RPGR) and RPGR-interacting protein (RPGRIP), within photoreceptor outer segments (OS) in a vertebrate retina with rods having multiple incisures. Methods: Photoreceptors and OS were dissociated from amphibian (Xenopus) retinas, treated to indirect immunofluorescence using purified polyclonal / monoclonal antibodies to RPGR, RPGRIP, α- and/or ß-tubulin, and examined by fluorescence microscopy. Results: A continuous streak of fluorescence to RPGR and to RPGRIP colocalized with the tubulin-fluorescent microtubules at the ciliary axoneme, which extended part way to the distal end of rod OS but all the way to the tip of cone OS. The OS of rods also displayed immunoreactivity to RPGR and to RPGRIP along longitudinal lines coinciding with their multiple incisures. At rod OS incisures, the anti-RPGRIP fluorescence formed continous lines that coincided with those of tubulin-immunoreactive microtubules, whereas the anti-RPGR fluorescence occurred as puncta at regular intervals (related to the daily cycle of rod OS renewal) along these lines. Conclusion: This similar, close association of RPGR and RPGRIP with the diverse microtubule-based cytoskeletal systems (the ciliary axoneme in rod and cone OS, the microtubules at multiple incisures in rod OS) in photoreceptor OS is likely important for RPGR and RPGRIP function. These findings may be clinically relevant because photoreceptor OS in amphibian retinas resemble those in human retinas (human rod OS have multiple incisures). The association of RPGR and RPGRIP with cytoskeletal systems that are somewhat different in the OS of rods and cones may help to clarify the different phenotypes of human pathologies (eg., Retinitis pigmentosa or Leber congenital amaurosis) that can be caused by gene defects in RPGR or RPGRIP.
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