Myelin Galactolipid Synthesis in Different Strains of Mice

Previous studies have indicated that the brains of DBA/2J (D2) mice have a more heavily myelinated CNS than those of C57BL/6J (B6) at postnatal days 17–21. However, the amount of myelin in the brains of F1 (B6 × D2) hybrids is even higher than in their parental strains. To investigate further factors involved in regulating myelino‐genesis in these mice, we have focused on the synthesis of cerebrosides and sulfatides, galactolipids enriched in myelin. Brain slices from 14‐, 17‐, and 21‐day‐old D2, B6, and F., mice were incubated with [ 3 H]galactose and [ 35 S]sulfate. After incubation, microsomes, myelin, and oligodendroglial cells were isolated, and the galactolipids were analyzed. At 21 days of age, the labeling of cerebrosides in F 1 mice was higher than in D2 and B6 mice when the results were expressed as microsomal or myelin radioactivity per gram wet weight. At 14 and 17 days of age, the labeling of cerebrosides in F 1 animals was similar to that in D2 mice and was considerably higher than that in B6 mice. The labeling of sulfatides in F 1 animals was significantly higher than in the B6 parent at all ages studied, whereas it remained higher than that in the D2 parent only at 17 days of age. A similar relationship among the strains was observed when the synthesis of myelin galactolipids was estimated by measuring the in vitro activity of UDP‐galactose:ceramide galactosyltransferase and 3′‐phosphoadenylyl sulfate:galactosylceramide 3′‐sulfotransferase. The results indicate that the increased accumulation of myelin galactolipids previously reported in the F 1 mice is partially due to enhanced synthetic activity.