Biochemical Study of Heterosis for Brain Myelin Content in Mice

Abstract: Heterosis (hybrid vigor) for brain myelin content has been examined in detail in (C57BL/6J × DBA/ 2J)F₁ hybrid mice at 17 days of age. The amount of myelin isolated from the F₁ hybrid brain is greater than that isolated from either parental strain. In addition, the total protein content in the myelin of the three genotypes showed the following trend: F₁ > DBA > C57. However, no discernible differences in myelin protein compositions could be detected by sodium dodecyl sulfate‐poly‐acrylamide gel electrophoresis. Analysis of the whole brain for several myelin‐associated constituents such as G_M1 ganglioside, 2′, 3′‐cyclic nucleotide 3′‐phosphohy‐drolase (CNPase), 5′‐nucleotidase and carbonic anhy‐drase indicated that heterosis exists for these components. No heterosis was found for such nonmyelin constituents as gangliosides G_DIa, G_T, G_Q, RNA, DNA and choline acetyltransferase. A developmental study of the whole brain CNPase indicated that the heterotic effect was greatest during the most active period of myelination (17–30 days). We conclude that the heterotic effect is specific for myelin content and is probably the result of an accelerated myelin synthesis. The heterotic effect should have great potential as a new model for studying aspects of myelinogenesis.