Cell‐Free Synthesis of Myelin Basic Proteins in Normal and Dysmyelinating Mutant Mice

Abstract

Total polyribosomes were isolated from the brains of 16- 20-day C57BL/6 mice, 4 neurological mutants (qk/qk, shi/shi, mld/mld, and jp/Y) and 4 heterozygote or littermate controls (qk/+, shi/+, mld, and jp littermates) and translated in a homologous, cell-free system. No differences were observed among the 9 genotypes in either the yield of polysomes (32.2 .+-. 0.6 A260/g brain) or in the incorporation of [35S] methionine into trichloroacetic acid-precipitable protein. When the 4 myelin basic proteins (BP) were isolated from the translation mixtures little incorporation of [35S]methionine into the BP was noted in those assays directed by polysomes from mld/mld or from shi/shi animals. Compared with C57BL/6 polysomes, mld littermate and shi/+ polysomes incorporated .apprx. 1/2 the levels of label into the 4 BP while qk/+ and qk/qk incorporated normal and close-to-normal levels. Polysomes from jp littermates and jp/Y brains synthesized 66% and < 15% of the levels of the 14K BP compared with C57BL/6 polysomes. Incorporation of label into the other 3 BP was normal with jp littermate polysomes and .apprx. 1/2 the control levels with jp/Y polysomes. The shi/shi and mld/mld mutants either produce altered BP not recognized by our antibody or synthesize very low levels of BP. The qk/qk mutant synthesizes much higher levels of MBP than are incorporated into myelin. In the jimpy mutant the synthesis of the 4 BP is affected to differing extents; thus, the mutant cannot be easily characterized as either an assembly or synthesis defect.