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J. Esteve-Rudd, L. Campello, L. Fernández-Sánchez, N. Cuenca, J. Martín-Nieto; Retinal Immunolocalization of the Ubiquitin-Proteasome System Ligases/Hydrolases, Parkin and UCH-L1. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4160.
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Parkin (an E3 ubiquitin ligase) and UCH-L1 (ubiquitin C-terminal hydrolase L1) are components of the ubiquitin-proteasomal system which, together with their substrate -synuclein, have been related to the etiology of both idiopathic and hereditary Parkinson disease. We are interested in studying their expression in the retina, and have so far reported the distribution profile of -synuclein in vertebrates (1). Here we address the expression of parkin and UCH-L1 genes at the mRNA and protein levels in the normal retina of mammals and describe their immunolocalization pattern.
Retinas from primate (human, monkey), bovine and rodent (rat, mouse) eyes were used in this work. RNA was isolated from the dissected neural retina and retinal pigment epithelium, and RT-PCR was performed using specific primers for the PARK2 and UCHL1 genes. Proteins extracted from both retinal fractions were subjected to immunoblotting analysis with parkin- or UCH-L1-specific antibodies. Retinal sections were incubated with primary antibodies to parkin or UCH-L1, and thereafter with fluorescently-labeled secondary antibodies. Images were obtained by laser-scanning confocal microscopy.
We have found expression of parkin and UCH-L1 mRNAs and proteins in the neural retina and retinal pigment epithelium of all species analyzed. Immunoblots revealed, in addition to the expected bands, higher- and lower-MW isoforms of both proteins. Parkin distributed throughout the retina, but was mainly expressed by photoreceptors, amacrines and ganglion cells, as well as by Müller glial cells. UCH-L1 localization was less widespread, but was found in the cell bodies and dendrites of most retinal neuronal types, including the two plexiform layers.
Both parkin and UCH-L1 genes and their protein products are expressed in the retina of all mammals studied. The different protein isoforms detected are indicative of mRNA alternative splicing and/or postranslational modifications. Their widespread distribution in the retina is suggestive of a relevant role in the ubiquitin-proteasomal pathway of protein degradation in retinal cells. Hence, their altered expression or dysfunction is expected to result in visual impairments.(1) Martínez-Navarrete, G.C., Martín-Nieto, J., Esteve-Rudd, J., Angulo, A. & Cuenca, N. (2007) Mol. Vis. 13: 949-961.
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