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G.J. Pauer, Q. Xi, M. Rayborn, J.G. Hollyfield, J. Wu, N.S. Peachey, S.A. Hagstrom; Expression of Tulp1 During Normal Mouse Development . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3976.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: TULP1, a member of a family of four proteins with unknown function designated tubby–like proteins or TULPs, is expressed specifically in photoreceptor cells. Mutations in TULP1 are associated with autosomal recessive retinitis pigmentosa and Tulp1 knockout mice develop an early–onset, progressive photoreceptor degeneration. To develop a body of information regarding mouse Tulp1, we analyzed the expression of mouse Tulp1 mRNA and protein during development and examined the retinal anatomy and function in young tulp1–/– mice. Methods: Tulp1 mRNA expression in wild–type (WT) mice was studied with quantitative RT–PCR while protein expression was observed using Western blot analysis and immunohistochemistry. Retinal function and anatomy in tulp1–/– mice was studied using electroretinography (ERG) and histology. Results: In WT retinas, Tulp1 mRNA was first detected at postnatal day (P) 1 and then increased incrementally to a stable peak at P11. Tulp1 protein expression paralleled the mRNA expression. At P15, the rod–mediated ERGs of tulp1–/– mice were reduced in amplitude, while cone–mediated ERGs were comparable to those recorded from WT littermates. Histologically at P15, the outer nuclear layer (ONL) of tulp1–/– retinas was normal in thickness, but the outer segments appeared slightly shorter than WT littermate controls. Small gaps near the outer limiting membrane were also seen in the ONL of tulp1–/– retinas that were not detected in the WT retinas. Conclusions: Tulp1 mRNA and protein are both detected in the developing mouse eye immediately following birth. In tulp1–/– mice, photoreceptor degeneration is apparent at an earlier age (P15) than previously described. At this early stage of photoreceptor degeneration, rod function is reduced to a greater extent than predicted from the anatomical presentation. In addition, cone function appears to be spared indicating that cones may be more resilient to the lack of Tulp1 and/or they degenerate at a later age due to an undefined secondary effect. These results indicate a fundamental role for TULP1 in maintaining the viability of rod photoreceptor cells.
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