Abstract
Abstract: :
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.
Keywords: 567 retinal pigment epithelium • 361 color pigments and opsins • 434 immunohistochemistry