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Nomingerel Tserentsoodol, Ying Hao, Paulo A. Ferreira; Characterization of the Genesis of the Outer Segments of Rod and Cone Photoreceptors Between Wild-type and RPGRIP1-/- Mice. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2664.
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© ARVO (1962-2015); The Authors (2016-present)
The Retinitis Pigmentosa GTPase Regulator Protein 1 (RPGRIP1) is a modular protein, which associates with the Retinitis Pigmentosa GTPase Regulator (RPGR) and nephrocystin-4 (NPHP4). This protein complex is implicated in syndromic photoreceptor dystrophies. Loss of RPGRIP1 suppresses the formation of the outer segments of photoreceptors followed by their rampant degeneration. This clinically underlies Leber congenital amaurosis. Hence, RPGRIP1 emerges as a master organizer of outer segment formation and morphogenesis of photoreceptors. The long-term goal of this study aims at defining how RPGRIP1 with its accessory partners determine the formation of outer segments in rod and cone photoreceptors.
We used immunohistochemical and ultrastructural methodologies allied to confocal and transmission electron microscopy to assess and compare the effects of loss of RPGRIP1 expression in rod and cone photoreceptors between wild-type and RPGRIP1-/- mice when outer segments begin to form.
Immunohistochemical analyses of P12 retinas of wild-type and RPGRIP1-/- mice with antibodies against RPGRIP1, partners thereof and other photoreceptors markers show that RPGRIP1 localizes proximally to NPHP4 and the ciliary marker, acetylated α-tubulin, and distally to centrin-2, a centriolar marker. Immunostained wild-type cilia with acetylated α-tubulin abut but do not colocalize with RPGRIP1, whereas NPHP4 protrudes partially into RPGRIP1 at a ciliary margin where they colocalize. RPGRIP1 partially colocalizes with centrin-2. In RPGRIP1-/- mice, no apparent changes in the localization of acetylated α-tubulin at the cilia and centrin2 are observed, but the cilia lack NPHP4, whose expression is also not detected anywhere in photoreceptors. The ultrastructure of cilia of wild-type and RPGRIP1-/- mice show undistinguishable development and size of ciliary structures, but RPGRIP1-/- mice present a ruffled ciliary membrane. All photoreceptor compartments (e.g. synaptic terminals and cell bodies) but the outer segment of rods and cones develop normally.
RPGRIP1 (and NPHP4) appears to localize to a transition zone of the mouse connecting cilium, which is contiguous and distal to and partially overlapping with centrin-2, and proximal but non-overlapping with acetylated α-tubulin. RPGRIP1 is required to the trafficking and ciliary targeting of NPHP4. The RPGRIP1 complex acts as a crucial accessory component of a trafficking complex, which among other functions affects the integrity of the ciliary membrane.
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