Oncomodulin Is Expressed Exclusively by Outer Hair Cells in the Organ of CortiNobuki Sakaguchia, Michael T. Henzlb, Isolde Thalmannc, Ruediger Thalmannc, and Bradley A. Schulteaa Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, South Carolina b Department of Biochemistry, University of Missouri, Columbia, Missouri c Department of Otolaryngology, Washington University School of Medicine, St Louis, Missouri Correspondence to: Bradley A. Schulte, Dept. of Pathology and Laboratory Medicine, Medical U. of South Carolina, 171 Ashley Ave., Charleston, SC 29425.
Oncomodulin (OM) is a small, acidic calcium-binding protein first discovered in a rat hepatoma and later found in placental cytotrophoblasts, the pre-implantation embryo, and in a wide variety of neoplastic tissues. OM was considered to be exclusively an oncofetal protein until its recent detection in extracts of the adult guinea pig's organ of Corti. Here we report that light and electron microscopic immunostaining of gerbil, rat, and mouse inner ears with a monoclonal antibody against recombinant rat OM localizes the protein exclusively in cochlear outer hair cells (OHCs). At the ultrastructural level, high gold labeling density was seen overlying the nucleus, cytoplasm, and the cuticular plate of gerbil OHCs. Few, if any, gold particles were present over intracellular organelles and the stereocilia. Staining of a wide range of similarly processed gerbil organs failed to detect immunoreactive OM in any other adult tissues. The mammalian genome encodes one Key Words: cochlea, calcium binding proteins, immunohistochemistry, parvalbumin, gerbil, rat, mouse
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