Myelin-deficient rat: analysis of myelin proteins.

Myelin basic protein (BP), proteolipid protein (PLP), myelin-associated glycoprotein (MAG), and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity were quantitated in the brains and spinal cords of normal and myelin-deficient (md) rats at 8, 12, 18, and 25 days of age. The levels of BP, MAG, and CNP in 25-day-old md brain were 1.1, 1.8, and 11% of those in controls, respectively. In spinal cord, the levels were higher, at 9, 15, and 12% of control values, respectively. Although BP content in the mutant rats was a lower percentage of the control level than MAG and CNPase contents at all ages, the absolute level of BP increased steadily between 8 and 25 days of age in both brain and spinal cord, whereas there was little change in the amounts of MAG and CNPase during this period. Immunoblotting analysis did not reveal an increased apparent Mr for MAG, as has been observed in quaking and trembler mice. There was little difference in the relative distributions of the 14K, 17K, 18.5K, and 21.5K forms of BP between control and md rat spinal cord homogenates at the ages examined. PLP content was reduced more than that of the other proteins in the md mutants, because it could not be detected by a technique capable of detecting 0.2% of the control brain level and 0.1% of control spinal cord level. This suggests that the expression of PLP may be preferentially affected in the md mutation.