Type II cytokeratin expression in adult vertebrate spinal cord

The phylogenetic evolution of the expression of type II cytokeratins (CKs) in the spinal cord of different adult vertebrates has been studied using an anti-CK immunohistochemical technique. Type II CK expression was stronger in lower vertebrates, specially anuran amphibians, than in higher vertebrates. No CK expression was found either in reptiles or birds, but a weak expression was demonstrated in mammals. The main neuroectodermal cell implicated in CK expression was the ependymocyte; some CK-positive radial astrocytes were also found in amphibians and fish, but neither CK-positive astrocytes nor neurons were observed in any vertebrate group. The functional significance of CK expression in the vertebrate spinal cord is not known. CKs do not have a consistent pattern of expression amongst vertebrates; however, the most common site is the ependyma.