Subretinal injection of rod outer segments leads to an increase in the number of early-stage melanosomes in retinal pigment epithelial cells

Our study was performed to test the hypothesis that sub-retinally injected protein can induce melanogenesis in the retinal pigment epithelium (RPE). R od outer segments (ROS) were isolated from cattle eyes and injected into th e subretinal space of Long Evans rats. Five days after surgery, the injecte d eyes were investigated by electron microscopy. The number of early-stage melanosomes and small melanin granules was compared in injected and noninje cted eyes. It was found that the injected ROS were phagocytized by the RPE cells, and the number of early-stage melanosomes in the RPE was significant ly increased in injected eyes compared to eyes without injection. The ROS-c ontaining endosomes fused with melanolysosomes in which melanogenesis took place. The increased number of early-stage melanosomes indicates new format ion of melanin. Copyright (C) 2000 S. Karaer AG. Basel.