Expression of myelin-specific proteins during development of normal and hypomyelinated Paralytic tremor mutant rabbits. II. Studies on the purified myelin.

An X-linked, recessive paralytic tremor (pt) mutation is characterized by CNS hypomyelination. In our previous work, we presented developmental studies on the expression of several myelin-specific proteins (PLP/DM-20, MBP, CNP, MAG, and MOG) in the brain homogeates of both pt mutant and age-matched control Chinchilla rabbits aged 1-120 postnatal days. A moderate reduction in all examined proteins and a striking PLP deficiency were observed in the pt mutant rabbits. In the present study, we investigated isolated and purified myelin fractions. A severe (approximately 30% of control values) and approximately constant hypomyelination of pt mutant CNS was observed during the entire investigated development (28-120 postnatal days). Although the neurological symptoms gradually regressed and a partial recovery of the affected animals usually occurred, no tendency toward regression of the hypomyelination was noticed. Whereas the content of CNP, MBP, and MAG in isolated myelin membrane fractions seemed close to normal, a drastic PLP deficiency was observed. A significantly elevated amount of MOG was found in the myelin of pt mutant rabbits. The controversy between the high degree of hypomyelination and the slight reduction in myelin protein marker expression (except for PLP) in mature brain homogenates is discussed with respect to retarded oligodendrocyte maturation and deficient processing of myelin membranes in pt mutant rabbits.