Endogenous cerebellar soluble lectin and its ligands in central nervous system myelin of quaking and jimpy mutant mice.
The presence of an endogenous 'cerebellar soluble lectin' (CSL) involved in myelin compaction and myelination was analyzed in the dysmyelinating mutant mice quaking and jimpy. The primary defect in these mutations with severe hypomyelination is still unknown in the quaking mutant but results from a single mutation in the proteolipid protein gene in the jimpy mutant. Both immunocytochemical and immunoblotting techniques showed that CSL was not considerably reduced in its expression in the myelin fraction purified from adult quaking mutants. Furthermore, the myelin-associated glycoprotein and an axonal glycoprotein with a relative molecular weight (Mr) of 31 kilodaltons (kDa) were not decreased in quaking mice. This contrasted with several glycoproteins of Mr 23, 18, 16 and 12 kDa which were absent from the purified quaking myelin. In myelin preparations obtained from the jimpy mutant the CSL level was considerably reduced. This defect did not result from a deficient synthesis of CSL. However, as in the quaking mutation low-Mr glycoproteins were lacking. The nature of the low-Mr glycoproteins absent in quaking and jimpy mice is discussed in relation to previous reports on myelin glycoproteins. In the various mutants, due to different primary mutations, a similar absence of myelin compaction was observed, which could be associated with a deficient level of low-Mr glycoproteins. It is thus postulated that these molecules are essential for ensuring myelin compaction as ligands for the endogenous CSL.