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S Peters, N Kociok, H Janicki, J Siodlaczek, U Schraermeyer; Tyrosinase is Present in Adult Mammalian Retinal Pigment Epithelium . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4557.
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Purpose: Tyrosinase and therefore melanin synthesis was commonly believed to be absent in postnatal retinal pigment epithelium (RPE). Only a few studies voiced some doubt about this hypothesis, taking into account the presence of premelanosomes and tyrosinase enzyme activity in the RPE. Methods:In vitro the following detection methods were applied on rat and human RPE before and after feeding of rod outer segments (ROS): RT-PCR, Western Blot, immunhistochemistry and demonstration of DOPA oxidase activity. Freshly enucleated eyes underwent immunhistochemistry with tyrosinase and rhodopsin antibodies at different times of day. Results: Tyrosinase was detected by immunhistochemistry in adult RPE in vivo and in vitro after feeding with ROS. A correlation with the time of the day in vivo and with the time after ROS-feeding in vitro was observed. Enzyme activity was found by DOPA reaction. RT-PCR demonstrated tyrosinase mRNA depending on ROS-exposure. Immunhistochemically tyrosinase colocalized with rhodopsin. Conclusion: This study demonstrates in vivo, that tyrosinase is present in adult mammalian RPE. A time dependancy was found related to the phagocytosis of ROS. The in vitro studies support this finding, demonstrating tyrosinase, enzyme activity and presence of mRNA.
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