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Scott R. Hudson, Teri Belecky-Adams, Vince Gattone, II, Caroline Miller; Meckelin 3 in Rat Photoreceptor Outer Segment Development. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5426.
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A group of ciliopathies has been associated with multiorgan pathology, including renal cysts and eye pathology. Previous studies have shown meckelin (protein product of the MKS3 gene) to be crucial to cilia function and its absence in the Wpk rat (with a mutated rMKS3 gene) causes a form of Leber’s congenital amaurosis. Retinal photoreceptors have a connecting cilium that joins the inner to the outer segment and plays a role in the transport of molecules necessary for morphological and molecular development and maintenance of the outer segment process. The present study evaluated the expression meckelin during normal rat outer segment retinal development in Wistar-Wpk/Wpk mutant rats.
Wpk mutant rats maintained in the Wistar background were anesthetized and then perfusion-fixed with 4% PF. The eyes were removed and the retinae frozen and cryosections cut which were immunolabeled by indirect immunofluorescence. Sections were analyzed using a Nikon Eclipse E800 with a Nikon Digital Camera DXM 1200 or an Olympus Fluoview FV 1000 confocal. Some retinae were embedded, and sectioned for transmission electron microscopy (EM). Thin sections were stained with uranyl acetate and viewed using a Tecnai G2 12 Bio Twin microscope.
Meckelin was co-expressed in photoreceptors, amacrine and ganglion cells in postnatal day 10 (P10) and P21 wild type retinae. In normal photoreceptors, MKS3 could be detected in both the inner and outer segments, as expected. By P10, both wild type and homozygous Wpk mutant retina appeared to have all retinal cell types. In contrast, by P21 the cells expressing photoreceptor-specific markers were fewer in number and showed an abnormal expression pattern. Analysis of EM sections showed the mutant photoreceptors did not develop an outer segment process beyond a connecting cilium and rudimentary outer segment.
We conclude that meckelin is not important for formation of connecting cilium and rudimentary outer segments, but is critical for the maturation and maintenance of the outer segment process.
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