Expression of oligo/polyα2,8-linked deaminoneuraminic acid and megalin during kidney development and maturation: mutually exclusive distribution with polyα2,8-linked N-acetylneuraminic acid of N-CAM
In tissues of higher organisms homopolymers of alpha2,8-linked N-acetylneuraminic acid can be found as a posttranslational modification on selected proteins. We report here the discovery of homopolymers of alpha2,8-linked deaminoneuraminic acid [poly(alpha2,8-KDN)] in various tissues derived from all three germ layers in vertebrates including mammals. The monoclonal antibody kdn8kdn in conjunction with a bacterial KDNase permitted the detection of poly(alpha2,8-KDN) by immunohistochemistry and immunoblotting. Further evidence for the existence of poly(alpha2,8-KDN) was obtained by gas/liquid chromatography. The poly(alpha2,8-KDN) glycan was detectable in all tissues studied with the exception of mucus-producing cells present in various organs, the extracellular matrix, and basement membranes. However, in certain organs such as muscle, kidney, lung, and brain its expression was developmentally regulated. Despite its widespread tissue distribution, the poly(alpha2,8-KDN) glycan was detected on a single 150-kDa glycoprotein except for a single >350-kDa glycoprotein in kidney, which makes it most distinctive among polysialic acids. The ubiquitous yet selective expression may be indicative of a general function of the poly(alpha2,8-KDN)-bearing glycoproteins.