Cytokeratin filaments and desmonsomes in the epithelioid cells of the perineurial and arachnoidal sheaths of some vertebrate species

Abstract

Abstract Using electron microscopy and immunohistochemistry with a large panel of antibodies to various cytoskeletal proteins we have noted that the singel- or multilayered sheaths of epithelioid cells (“neurothelia”) surrounding periopheral nerves (perineurial cells) or structres of the central nerous system, including the optic nerve (arachnoid cells), show remarkable interspecies differences in their cytoskeletal complements. In two anuran amphibia examined ( Xenopus laevis, Rana ridibunda), the cells of both froms of neuraothelia, i.e., perineurial and arachnoid, are interconnnected hy true desmosomes and are rich in intermediate-sized filaments (IFs) of the cytokeratin type. Among higher vertebrates, a similar situation is found in the bovine and chicken nervous systems, in which the arachnoid cells of the meninges contain desmosomes and IFs of both the cytokeratin (apparently with restricted epitope accessibilities in the chicken) and the vimentin tupe, whereas the perineurial cells of many nerves contain cytokeratin IFs, often together with vimentin, but no desmosomes. In contrast, in rat arachnoidal and perineurial cells significant reactions have been observed neither for cytokeratins nor for desmosomes. In the human nervous system, cytokeratins and desmosomes have also not been seen in thevarious perineuria studied whereas desmosomes are frequent in arachnoidal cell layers which are dominated by vimentin IFs and only in certain small regions of the brain contain some additional cytokeratins. The occurrence of cytokeratins in the tissues found positive by immunohistochemistry has been confirmed by gel electrophoresis of cytoskeletal proteins, followed by immunoblottting. Our results emphasize both similarities and differences between the neurothelia on the one hand and epithelia or endothelia on the other, justifying classificaiton as a separate kind of tissue, i. e., neurothelium. The observatons of interspecies differences lead tp the challenging conclusion thaht neither desmosomes nor cytokeratins are essential for the basic functions of neurothelial sheaths nor does the specific type of IF protein expressed in these cells appear to matter in this respect. The results are also discussed in relation to the cytoskeletal characteristicis of other epithelioid tissues and of human neurothelium-derived tumors.