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I. C. Han, J. Tyrrell, P. Yang, G. J. Jaffe; Survival Factor Expression and Distribution in Wild-Type Mouse Eyes. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3054. doi: https://doi.org/.
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The dynamic balance between pro and anti-apoptotic factors determines cell survival in normal eyes and those with posterior segment diseases such as AMD and retinal degenerations. We have shown previously that the survival factors c-IAP1, c-IAP2, TRAF-1, TRAF-2, Bcl-x, Bcl-xL, and c-FLIP are basally expressed in both cultured human retinal pigment epithelial (RPE) cells and fresh RPE cell isolates from human donor eyes, with Bcl-xL being the most highly expressed factor tested. Here we determined the expression and distribution of these survival factors in wild-type mouse eyes.
Eyes were removed from wild-type C5BL/6 mice and dissected into samples of whole eye cup, RPE and retina, or choroid and sclera. Following RNA extraction, expression of various survival factors was analyzed with gene-specific primers using real-time RT-PCR. Immunohistochemistry with anti-Bcl-xL primary and Alexa-594 secondary antibody was performed to localize Bcl-xL in cryosections of both mouse and human eye cups.
Basal mRNA expression was observed in the mouse eye for all survival factors tested, though the relative levels of expression varied among different tissues. In the mouse eye cup, c-IAP1 and c-FLIP were the most highly expressed genes, while TRAF-1 and survivin were expressed at very low levels when compared to the PPIA housekeeping gene. In the RPE-retina, Bcl-xL was the most highly expressed gene, while c-IAP1 and c-FLIP were only expressed at intermediate levels. In contrast, in the choroid-sclera, c-FLIP was the most highly expressed gene, while Bcl-xL and c-IAP2 were expressed at intermediate levels. By immunohistochemistry of wild-type mouse eye cup cryosections, Bcl-xL was identified in all retinal layers, with particularly strong staining in both the inner and outer plexiform layers and relatively faint staining in the RPE. In contrast, in sections of human eyes, immunostaining for Bcl-xL generates a particularly strong signal in the RPE and the ganglion cell layer, with relatively low levels of staining throughout the retina.
The relative expression of survival factors may vary in different posterior segment eye tissues. Localization and expression of the same survival factors may also differ in mouse eyes compared to human eyes. In disease models of AMD and retinal degenerations, consideration of these survival factor variations is especially important when planning in vivo and in vitro experiments or when comparing human pathology to animal models.
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