Reactivity of Tissue-Specific Antigens in N-Methyl-N'-Nitro-N-Nitrosoguanidine-Induced Neoplasms and Normal Tissues from Medaka (Oryzias latipes)*1

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Abstract
To further characterize the distribution of tissue-specific antigens in fish neoplasms, juvenile medaka were exposed to 30 mg/L of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 1 hr and allowed to grow out for up to 16 mo. Using a streptavidin peroxidase technique, keratin, vimentin, and neurofilament intermediate filament proteins, and actin and S-100 proteins were labeled in MNNGinduced neoplasms and normal medaka tissues using specific monoclonal or polyclonal antibodies. In vascular tumors, rhabdomyosarcoma, and teratoma, muscle tissues were positive for actin. Other sarcomas including hemangiopericytoma, fascial sarcoma, and undifferentiated sarcoma were negative for all antibodies tested. An unusual scale-associated neoplasm, composed of clusters of scale-forming cells surrounding spicules of scale, had keratin-positive stroma. The epithelial neoplasms were also positive for keratin, except for pancreatic acinar carcinoma, which had limited positivity. Both teratoma and olfactory carcinoma had S-100-positive intraepithelial cells morphologically reminiscent of neurosensory epithelial cells, which were S-100 positive in normal tissues. Although positive reactivity in fish tissues correlated with mammalian data, the antibodies used were raised against mammalian antigens. Therefore, a negative reation may be indicative of lack of antibody sensitivity to specific fish antigens rather than absence of the antigen in the tissues. However, these data show that tissue-specific antigen detection may assist in elucidating the biology of neoplasia in fish.