SC1, an immunoglobulin superfamily cell adhesion molecule, is transiently expressed during avian embryogenesis by a variety of cell types. This molecule has a homophilic binding activity with SC1 itself and promotes neurite projection from embryonic neurons. However, the potential role of this molecule in pathologic tissue specimens from chickens has yet to be elucidated. In this study, we examined the expression and functional role of SC1 in the sporadic nephroblastomas of chickens. Western blot analysis showed SC1 to be recognized as approximately 100 kDa and enriched in embryonic metanephros with a lower level in the adult kidney, while it was overexpressed in nephroblastomas. Immunohistochemically, SC1 was abundantly found in the tubular epithelia and blastemal cells of embryonic metanephros. In contrast, it had almost completely disappeared in the adult kidney; parts of the distal convoluted and intermediated tubules, collecting ducts, and Bowman's capsule slightly expressed SC1. In all 32 cases of nephroblastoma, SC1 was overexpressed in most characteristic components in tumors such as neoplastic epithelia with various types of differentiation, blastemal cell condensations, and glomeruloid bodies. Primary culture cells from a nephroblastoma expressed SC1 on the cell surface, whereas cells from the adult kidney showed only weak expression. A cell aggregation assay revealed that the dissociated cells from a nephroblastoma have strong aggregation activity, which was inhibited by anti-SC1 antibody. In contrast, the self-aggregation of adult chicken kidney cells was weaker than that of the tumor and not inhibited by the antibody. These findings suggest that the expression of SC1 might play a potential role in both the structural formation of nephroblastomas, based on its adhesive activity, and normal renal development.

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