The Endogenous Lectin Cerebellar Soluble Lectin and Its Ligands in Central Nervous System Myelin of Myelin‐Deficient (mld) Mutant Mice

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Abstract
The myelin-deficient (mld) mutation is autosomal recessive mutation in the murine CNS exhibiting severe hypomyelination. The primary defect results in a drastic reduction of myelin basic protein synthesis caused by a duplication of the myelin basic protein gene with partial inversion of the upstream gene copy. The severe deficit of myelin basic protein is responsible for the absence of the major dense line but cannot explain the heterogeneity of myelin compaction found in mld. We have tested the hypothesis that the endogenous cerebellar soluble lectin (CSL) and/or its endogenous glycoprotein ligands could be involved in myelin abnormalities in the dysmyelinating mutant, mld. Immunocytochemical and immunoblotting techniques showed that the CSL level was not reduced significantly in the mld mutant. Furthermore, two ligands of CSL, the myelin-associated glycoprotein and an axonal glycoprotein, with a relative molecular mass of 31 kDa, were not decreased in level in the purified myelin fraction isolated from mld mice. In contrast, three minor glycoprotein ligands of CSL of relative molecular mass of 23, 18, and 16 kDa were greatly reduced in content. The reduced concentration of these low-molecular-mass glycoproteins in mld myelin suggests that they are constituents of compact myelin. Furthermore, the observation that CSL is specifically localized in vivo in regions where mld myelin is more compact and absent from regions devoid of myelin compaction may suggest that the endogenous CSL lectin, as well as its minor glycoprotein ligands, plays a role in the stabilization of the myelin sheath.