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Livia S Carvalho, Valentina Voigt, Iona Schuster, Paula Fuller-Carter, Juan Pablo Quesada, Sophia Vasiliou, David M Hunt; Validation and comparison of Achromatopsia mouse lines expressing a fluorescent marker in cone photoreceptors. Invest. Ophthalmol. Vis. Sci. 2018;59(9):970.
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© ARVO (1962-2015); The Authors (2016-present)
Achromatopsia (ACHM) is an inherited early-onset disease that affects cone photoreceptors. Clinical symptoms start at birth and include absent or impaired color discrimination, no recordable cone ERGs, poor visual acuity and severe photophobia. Mutations in 6 genes have been shown to cause ACHM and in vivo imaging shows a variable range of cone photoreceptor integrities and structures between genotypes. However, research into cone disease mechanisms is complicated by the paucity of cones since they account for only 3% of photoreceptors. The purpose of this study was to establish a detailed comparison of 3 ACHM mouse models and validate crosses of these models with a mouse expressing a fluorescent protein in cones.
Cone cell death in three different ACHM models (Pde6ccpfl1, Cnga3-/- and Gnat2cpfl5) was quantified by TUNEL and a retinal immune cell profile was characterised by flow cytometry. To quantify cone numbers via flow cytometry, the Chrnb4.GFP mouse, where cones express GFP, was crossed with the ACHM models. The newly generated ACHM lines with GFP-expressing cones were validated against the original lines via ERGs and morphological analysis.
TUNEL analysis shows a peak of cell death at 24 days old for all 3 models. Interestingly, in the Cnga3, a second cell death peak is present at 40 days. All 3 models, show a delay in the retinal pruning stage compared to wildtype (wt), whereas the retinal immune cell profile in all three models is not significantly different from wt. The GFP-expressing ACHM lines show similar ERG response and retinal morphology to the original ACHM lines. Analysis of cone numbers show significantly different disease progression between the models, with Pde6c being the most severely affected.
The results presented here indicate that cell death timing is similar between the models and that an immune response is not active during later stages of degeneration. However, it would appear that a lack of functional phototransduction proteins might cause a delay in cone migration and/or pruning. Furthermore, there might be molecular and cellular differences between the ACHM genotypes which result in differential rates of cone survival. Finally, the results here validate the use of a fluorescent-labelled cone model; this will allow for more detailed studies into cone degeneration mechanisms.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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