Immunohistochemical localization of MUC1 glycoprotein in the retina.

Glycoconjugates on the photoreceptor cell surfaces and in the interphotoreceptor matrix (IPM) are involved in a variety of cell functions. The O-linked glycoconjugates, seen in the filaments of IPM by electron microscopy,’ may connect the neural retina with the retinal pigment epithelium (RPE) in the subretinal space.’ These O-linked glycoconjugates are found on the surfaces of both cone and rod photoreceptors except for the basal one-fourth of the inner segments, about the height of Miiller cell fiber baskets.3 These observations led us to speculate that Olinked glycoconjugates in the IPM may link the RPE-processes to the Miiller cell fiber baskets, on which some acceptors for glycoconjugates may be present. MUC 1 glycoprotein, the first mucin to be cloned, is localized on the apical surfaces of epithelial cells as a transmembrane, polymorphic glycoprotein.4 We recently examined the immunohistochemical distribution of MUC 1 in various tumors of the eyelid, orbit, and eyeball.5 During examination of the eyeball tumors, we noted a preferential distribution of MUC 1 in the retinal region that was free of tumor cells. We report this finding because MUC 1 appears to be one of the acceptors on Miiller cell fibers for the O-linked glycoconjugates in the IPM. One eyeball with retinoblastoma and two eyeballs with choroidal melanoma were enucleated and histopathologically examined; immunohistochemical examination of MUC 1 was done on the tumor-free retinal areas. The eyeballs were immersion fixed with buffer formalin at 4°C overnight, rinsed in Dul-