The endogenous lectin cerebellar soluble lectin and its ligands in central nervous system myelin of myelin-deficient (mld) mutant mice

Cerebellar soluble lectin and its glycoprotein ligands in the developing brain of control and dysmyelinating mutant mice

The levels of an endogenous lectin, the cerebellar soluble lectin (CSL) and of its endogenous glycoprotein ligands were studied using immunoblotting and affinoblotting techniques in the forebrain of quaking, shiverer and jimpy dysmyelinating mutant mice and their respective control littermates during the postnatal development. In the controls of the mutant mice, the level of CSL showed an important increase between days 5-18 then a stabilization, although at all ages the level of CSL was reduced (at least 15%) in the control littermate of the shiverer mutant. In the shiverer mutant the developmental pattern is similar to the control but was reduced by 50% as compared to the control. In the jimpy mutant an erratic development of CSL was observed which was with quasi absence of CSL at days 12 and 25. Variation of CSL levels in the quaking brain were also observed. CSL glycoprotein ligands also showed variable developmental profiles with a special persistence with ageing of CSL-binding glycoproteins in the quaking and jimpy mice. Developmental variations were also observed between the different control littermates. These results are discussed in view of developmental roles attributed to CSL and its glycoproteins ligands in cell adhesion mechanism during brain ontogenesis and especially myelination.

Glycoproteins and lectins in cell adhesion and cell recognition processes

The discovery of endogenous lectins having specific and high affinity for the carbohydrate portions of glycoproteins has opened up new directions in the field of cell adhesion and cell recognition. Two endogenous lectins, termed as CSL and R1, initially isolated from the rat cerebellum and having a wide distribution in mammalian tissues, have been shown to participate in essential mechanisms of cell adhesion. The membrane-bound lectin R1 seems to be involved in transient recognition between neuronal cells, followed by elimination of the glycoprotein ligands at the surface of the recognized cell. In contrast, CSL is a molecule involved in adhesion between various normal or transformed cells since it participates in the formation of tight junctions. The glycoprotein ligands recognized with higher affinity by these two lectins seem to possess a special structure which defines a sub-class of oncofetal HNK-1 glycans. The over-expression of the glycoprotein ligands of these lectins in most transformed cells provides new tools for understanding the underlying mechanism of malignant transformation as well as the generation of signals through cell adhesion.

Purification and partial structural and functional characterization of mouse myelin/oligodendrocyte glycoprotein

The myelin/oligodendrocyte glycoprotein (MOG) is found exclusively in the CNS, where it is localized on the surface of myelin and oligodendrocyte cytoplasmic membranes. The monoclonal antibody 8-18C5 identifies MOG. Several studies have shown that anti-MOG antibodies can induce demyelination, thus inferring an important role in myelin stability. In this study, we demonstrate that MOG consists of two polypeptides, with molecular masses of 26 and 28 kDa. This doublet becomes a single 25-kDa band after deglycosylation with trifluoromethanesulfonic acid or peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase, indicating that there are no or few O-linked sugars and that the doublet band represents differential glycosylation. Partial trypsin cleavage, which also gave a doublet band of lower molecular weight, confirmed this idea. MOG was purified by polyacrylamide gel electrophoresis, followed by electroelution. Three N-terminal sequences of eight to 26 amino acids were obtained. By western blot analysis, no binding was found between MOG and cerebellar soluble lectin. MOG does not seem to belong to the signal-transducing GTP-binding proteins. Reduced MOG concentrations were observed in jimpy and quaking dysmyelinating mutant mice, giving further support to its localization in compact myelin of the CNS.

Endogenous lectin cerebellar soluble lectin involved in myelination is absent from nonmyelinating Schwann cells

In the sciatic nerve, two major classes of Schwann cells are present which differ in their capability to produce myelin. Myelinating Schwann cells surround most of the axons with the formation of a typical myelin sheath. Nonmyelinating Schwann cells serve to insulate individual axons without formation of myelin. These dissimilarities between the two types of Schwann cells provided an interesting model for studying mechanisms underlying myelination and the formation of contacts between axons and myelinating cells. It is demonstrated here that the endogenous lectin cerebellar soluble lectin (CSL), implicated in myelin stabilization and in formation of contact between axon and myelinating cells in the CNS and in the sciatic nerve, is undetectable in non-myelinating Schwann cells. In contrast, most axons surrounded by these cells contained the major axonal glycoprotein ligand of CSL, a 31-kDa glycoprotein which is present in large amounts. The possible relationship between the presence of CSL in Schwann cells and their capacity to interact with axons and to produce myelin are discussed.