GLIAL-CELLS OF THE LAMPREY NERVOUS-SYSTEM CONTAIN KERATIN-LIKE PROTEINS

Lamprey axons regenerate following spinal cord transection despite the formation of a glial scar. As we were unable to detect a lamprey homo logue of glial fibrillary acidic protein (GFAP), a major constituent o f astrocytes, we studied the composition of intermediate filament (IF) proteins of lamprey glia. Monoclonal antibodies (mAbs) were raised to lamprey spinal cord cytoskeletal extracts and these mAbs were charact erized by using Western blotting and immunocytochemistry. On two-dimen sional (2-D) Western blots, five of the mAbs detected three major IF p olypeptides in the molecular weight (MW) range of 45-56 kD. Further st udies were conducted to determine the relationship between the lamprey glial-specific antigen and other mammalian IF proteins. Antikeratin 8 antibody recognized two of the three polypeptides. Several of the gli al-specific mAbs reacted with human keratins 8 and 18 on Western blots . Keratin-like immunoreactivity was found in all parts of the central and peripheral nervous systems in both larval and adult lampreys. The immunocytochemical staining patterns of glial-specific mAbs were indis tinguishable on lamprey spinal cord sections. However, on brain sectio ns, two distinct patterns were observed. A subset of mAbs stained only a few glial fibers in the brain, whereas others stained many more bra in glia, particularly the ependymal cells. The former group of mAbs re cognized only the two lower MW polypeptides on 2-D Western blots, but the latter group of mAbs recognized all three major IF polypeptides. T his correlation is supported by the observation that the highest MW IF polypeptide has an increased level of expression in the brain relativ e to the spinal cord. Thus, in the lamprey, the glial cells of both sp inal cord and brain express molecules similar to simple epithelial cyt okeratins, but their Ifs may contain these keratins in different stoic hiometric proportions. The widespread presence in the lamprey of primi tive glial cells containing keratin-like intermediate filaments may ha ve significance for the extraordinary ability of lamprey spinal axons to regenerate. (C) 1995 Wiley-Liss, Inc.