Cytokeratin-filament expression in epithelial and non-epithelial tissues of the common carp (Cyprinus carpio)

Cytokeratin expression in mammals is generally restricted to epithelial cells and has been utilized to differentiate epithelial from nonepithelial tissues in these species. Since cytokeratins have been shown to be highly conserved during vertebrate evolution, the objective of the present study has been to ascertain the expression pattern of cytokeratins in tissues of the common carp (Cyprinus carpio). A panel of 10 anti-human cytokeratin antibodies was evaluated using a streptavidin-biotin-peroxidase complex detection system. Tissues were fixed in 10% neutral-buffered formalin, 100% ethanol or methacarn. Only formalin-fixed tissues were pre-digested with trypsin prior to immunostaining. Formalin-fixed tissues generally resulted in a less intense, more diffuse staining pattern with considerable background compared with ethanol and methacarn and was therefore the least desirable fixative. The diverse staining pattern observed with the various antibodies used in this study was consistent with previous findings in other teleosts. The results confirm that cytokeratin expression in teleosts is fundamentally different from that in mammals and therefore should be used as a method to differentiate epithelial cell types in these species only with discretion.