Cytokeratins in the liver of the sea lamprey (Petromyzon marinus) before and after metamorphosis

Abstract.

Cytokeratins of the liver were examined during the lamprey life cycle. This organ transforms, at metamorphosis, from a ductal larval structure to an aductal adult organ lacking the biliary passageways. Specifically, the relationship between liver morphology and cytokeratins 7, 18, and 19, and several unidentified cytokeratins was compared in larvae, transformers, and adults. Immunofluorescence staining showed that spatiotemporal cytokeratin distributions are cell-type-specific among hepatocytes, bile-duct cells, and gallbladder cells. In the larva, cytokeratins 7 and 19, and other unknown cytokeratins occur diffusely in the hepatocyte cytoplasm and prominently in the apices of hepatocytes near a bile canaliculus, so that collectively these cytokeratins form a pericanalicular ring. At mid-metamorphosis, the ring disappears, and cytokeratins are located predominantly in the periphery of bile-duct cells. In the adult, cytokeratin 19 has a sexually dimorphic distribution. Electrophoretic separations of cytoskeletal extracts of larval and adult livers have revealed larval cytokeratins 46, 49, 58, and 63.5, and adult male cytokeratins 46, 48, 49, 52.5, 58, 63.5, 64.5, 65, and 66. Immunoblotting has shown that certain cytokeratins are each related to at least two mammalian cytokeratins. We suggest that lamprey-specific liver cytokeratins exist, and that the metamorphosing liver can be used as a model for studying the relationship between cytokeratin organization and cell function.