Myelin subfractions isolated from mouse brain. Studies of normal mice during development, quaking mutants, and three brain regions

Abstract

Myelin isolated from three areas of mouse brain, from whole brain at several ages in normal mice, and from whole brain of adult quaking mutant mice was separated into seven bands and a pellet on discontinuous density gradients using 0.32, 0.45, 0.55, 0.60, 0.70, 0.75 and 0.85 M sucrose. The distribution of myelin in the subfractions was independent of homogenization and shocking conditions employed to isolate the myelin preparations, but was related to the type of myelin applied to the gradient. Compared to myelin isolated from older animals, myelin isolated from 18-24 day old mice displayed a distribution pattern with greater proportions of material banding at lesser sucrose densities. Similarly, myelin obtained from hindbrain contained proportionately more material layering at lesser sucrose densities compared to myelin isolated from cerebral cortex. Myelin subfraction patterns observed for 8-12 day old control mice and quaking mutants were unlike each other or any other myelin preparation examined. In the 18-90 days old animals, the markers studied were not uniformly distributed among the myelin subfractions. The pellet and the layer banding at the 0.75/0.85 M sucrose interface contained the highest specific concentrations of sialic acid, nucleic acid, and total adenosine triphosphatase activity. In contrast, the specific activity of 2',3'-cyclicnucleotide-3'-phosphohydrolase was lowest in the pellet as well as the three bands obtained above 0.60 M sucrose and was highest in the fraction banding at the 0.65/0.70 M sucrose interface. The results obtained were not consistent with an artifactual origin of the myelin subfractions, but instead suggested that the subfraction have physiological significance. One explanation for the different banding patterns observed between young and mature myelin may be the different amount of myelin in various brain regions during development.

Changes in Sciatic Nerve Protein Composition during Postnatal Development of Mice

“…Developmental alterations observed in this study are in general agreement with several CNS myelin studies [Konat and Clausen, 1978;Malthieu et al, 1978;Chou et a!., 1978: Sheads et al. 1977, Overall changes in total myelin proteins occur in PNS development without a large variation in the relative concentrations of each species of myelin protein.…”

“…Such changes appear con sistent with the heterogeneous densities of myelin, apparent during development [Sheads et al, 1977] and the 'light'-'heavy' myelin dichotomy also reported [Banik and Smith, 1977] in developing CNS. Whereas CNS myelin appears to exhibit decreasing density with increasing development due to the accumulation of light basic proteins and the relative dilution of the heavy Wolfgram protein [Banik and Smith, 1977; Kelly and BPF proteins slowly continue to accumulate in relative concentration through 50 days postnatally.…”

“…In fact, it appears that Wolfgram protein which is prominent in CNS developing myelin Langes, 1976: Banik andSmith, 1977;Sheads et al, 1977] may not occur in the postnatally de veloping sciatic nerve. The most striking ob servation in nerve development is that the myelin proteins appear in nearly equal rela tive concentrations throughout development.…”

“…The most striking ob servation in nerve development is that the myelin proteins appear in nearly equal rela tive concentrations throughout development. This closely regulated factor in myelin pro teins is also seen in myelin alterations of the CNS or PNS whether produced by genetic errors [Matthieu et al, 1978;Sheads et al. 1977], by disease [Chou et ah, 1978;Singh and Spritz, 1974] or degeneration [Lunges et al.…”

“…In contrast, a number of recent studies [Griffith et al, 1970;Grossfeld and Shooter, 1971;Cain et al, 1972;Waehneldt and Neuioff, 1974;Morell et al, 1972;Kelly and Luttges, 1976;Banik and Smith, 1977;Sheads et al, 1977] have dealt with developmental changes in proteins from the central nervous system (CNS). Differences between PNS and CNS proteins are well documented [Brostoff •t al., 1971;Everly et al, 1973;Greenfield et a/., 1973;Mahl and Wolfgram, 1969;Singh and Spritz, 1974;Luttges et al, 1976;Kelly and Luttges, 1976;Wood and Dawson, 1974;Wigginsetal., 1975]; nevertheless, only two studies have been devoted to a comprehensive survey of PNS protein changes during postnatal development.…”