Expression of actin and desmin in experimentally induced hepatic lesions and neoplasms from medaka (Oryzias latipes).

Proliferation of stromal cells is a common occurrence in experimentally induced hepatocarcinogenesis in fish. However, the role of these cells in fish hepatic injury and neoplasia is unknown. To better understand the biology of the cells comprising the hepatic stroma, livers from medaka (Oryzias latipes) experimentally induced by diethylnitrosamine or methylazoxymethanol acetate were labeled with keratin, actin, and desmin antibodies. The distribution of these proteins in hepatocellular carcinoma, cholangiocarcinoma, spindle cell proliferative lesions, and spongiosis hepatis was assessed, including three peritoneal sarcomas for comparison. Ductular epithelial cells in cholangiocarcinoma were positive for keratin, with desmin and actin positive ductular walls. Presumptive perisinusoidal cells in primarily trabecular and schirrous hepatocellular carcinoma were also actin positive. Only one spindle cell proliferative lesion was positive for any of the antibodies (desmin), and this lesion was morphologically distinct from others in the same category. Spongiosis hepatis, the peritoneal sarcomas, and normal perisinusoidal and other stromal cells were negative for these proteins. Since actin and desmin can be alternatively or coexpressed by mammalian perisinusoidal cells in association with hepatic fibrosis and neoplasia, the present studies suggest these proteins may serve as functional markers of hepatic stromal cells in fish as well.