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Cassandra L Ondeck, Justin Etzel, Yuanjun Zhao, Alistair J Barber, Jeffrey Sundstrom; Expression patterns of the short fibulins in the rat retina.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6540.
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© ARVO (1962-2015); The Authors (2016-present)
The fibulin family is comprised of seven glycoproteins (designated FBLN 1-7), thought to be secreted into the extracellular matrix and basement membranes, and binding with fibronectin, laminin and proteoglycans. The fibulins share several common features including repeated epidermal growth factor-like domains and a unique C-terminus domain. A point mutation in the EFEMP1 gene (encoding FBLN-3) is known to be associated with Doyne honeycomb retinal dystrophy. Several mutations in FBLN-5 are also associated with the development of age related macular degeneration. Despite the potential importance of the fibulins in retinal disease there has been little characterization of their expression patterns in the eye. Therefore the purpose of this study was to determine the expression patterns of the short fibulin proteins in the normal rat eye.
Eyes were enucleated from healthy male Long-Evans rats and preserved by flash-freezing. All procedures were in accordance with the Penn State Hershey College of Medicine IACUC and the ARVO guidelines for use of animals in ophthalmology research. Frozen sections were fixed and probed with primary antibodies to FBLN-3, -4, -5 and -7, and labeled for confocal microscopy imaging (Leica SP8).
Confocal microscopy revealed positive immunoreactivity for FBLN-3 concentrated in the retinal pigment epithelia (RPE) with a punctate distribution, and in the extracellular space between RPE and photoreceptor outer segments (OS). Immunoreactivity for FBLN-4 and -5 appeared similar to each other, with diffuse distribution throughout the retina, concentrated in the plexiform layers and the OS. FBLN-7 immunoreactivity was located exclusively on the surface of the inner retina but did not colocalize with glial fibrillary acidic protein and was especially abundant at the optic nerve head.
Despite their relatively similar molecular structures the fibulins have a diverse distribution in the rat retina. FBLN-3 is exclusively expressed by the RPE and also appears to be part of a matrix in the space between the RPE and OS. FBLN-4 and -5 appear to be abundant throughout the cytoplasm of most retinal neurons and possibly Muller cells. FBLN-7 appears to be exclusively expressed in the axoplasm of retinal ganglion cells and is heavily concentrated at the head of the optic nerve. Given the diverse distribution of fibulins it is likely that these proteins have different functions in the retina.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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