Myelin differences in the central and peripheral nervous system in the 'Jimpy' mouse

Severe Convulsions and Dysmyelination in Both Jimpy and Cx32/47 -/- Mice may Associate Astrocytic L-Channel Function with Myelination and Oligodendrocytic Connexins with Internodal Kv Channels

The Jimpy mouse illustrates the importance of interactions between astrocytes and oligodendrocytes. It has a mutation in Plp coding for proteolipid protein and DM20. Its behavior is normal at birth but from the age of ~2 weeks it shows severe convulsions associated with oligodendrocyte/myelination deficits and early death. A normally occurring increase in oxygen consumption by highly elevated K+ concentrations is absent in Jimpy brain slices and cultured astrocytes, reflecting that Plp at early embryonic stages affects common precursors as also shown by the ability of conditioned medium from normal astrocytes to counteract histological abnormalities. This metabolic response is now known to reflect opening of L-channels for Ca2+. The resulting deficiency in Ca2+ entry has many consequences, including lack of K+-stimulated glycogenolysis and release of gliotransmitter ATP. Lack of purinergic stimulation compromises oligodendrocyte survival and myelination and affects connexins and K+ channels. Mice lacking the oligodendrocytic connexins Cx32 and 47 show similar neurological dysfunction as Jimpy. This possibly reflects that K+ released by intermodal axonal Kv channels is transported underneath a loosened myelin sheath instead of reaching the extracellular space via connexin-mediated transport to oligodendrocytes, followed by release and astrocytic Na+,K+-ATPase-driven uptake with subsequent Kir4.1-facilitated release and neuronal uptake.

Microglial cell reaction in the gray and white matter in spinal cords from jimpy mice. An enzyme histochemical study at the light and electron microscope level

Jimpy is a genetic disorder which results in a severe hypomyelination in the central nervous system associated with a variety of astroglial and oligodendroglial abnormalities. In this study, we examined the morphology and distribution of microglial cells in spinal cord sections from jimpy and normal mice at 10-12 and 20-22 days postnatal using a specific microglial marker, the nucleoside diphosphatase staining. Compared to those of normal littermates, the spinal cords of jimpy mice showed an intense microglial cell reaction in white and gray matter, as revealed by quantitative analysis and light and electron microscope study. Microglial reactivity was apparent in all spinal cord areas, although it was more pronounced in white than in gray matter. The mean microglial densities in the jimpy white matter were about threefold (10-12 days) and fivefold (20-22 days) higher than in the normal, whereas in the gray matter, microglial density in jimpy was about 60% higher than in normal at both ages. Morphologically, microglial cells in the normal spinal cord showed a ramified appearance, similar in size and ramification pattern to those reported in other normal CNS areas. In contrast, microglial cells in the jimpy spinal cord showed a reactive morphology, characterized by a shortening and coarsening of their cell processes, swelling of their cell body and accumulation of lipid inclusions. Reactive microglial cells were found in close association with axons and oligodendroglial cells. The possible role of microglial cells in hypomyelination is discussed.

Differential regulation of cerebroside sulfotransferase and 2',3'-cyclic nucleotide 3'-phosphodiesterase by basic fibroblast growth factor in relation to proliferation in rat oligodendrocyte cultures

Previous results (Fressinaud, C., Sarliève, L.L., and Labourdette, G. J. J. Cell. Physiol., 141:667-674, 1989b) have shown that cerebroside sulfotransferase (CST; EC 2.8.2.11) is enriched in pure rat oligodendrocyte (OL) cultures and that its activity is increased by factors mitogenic for OL precursors and galactocerebroside (GC) expressing OL, such as basic fibroblast growth factor (bFGF), platelet-derived growth factor, and high insulin concentrations. In contrast, transforming growth factor beta or low insulin concentrations were found to be ineffective in this culture system. As bFGF mainly enhanced the proliferation of OL precursors (GC negative cells) rather than that of differentiated (GC+) cells, a relationship between OL precursor proliferation and CST increase was suggested. This hypothesis was first tested in 20-day-old OL cultures grown in chemically defined medium. The dose-response curve of [125I] Iododeoxyuridine ([125I]dUrd) incorporation toward bFGF was parallel to that of CST specific activity, and maximal stimulation was reached at 5 ng/ml bFGF for both. In contrast, 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP; EC 3.1.4.37) specific activity decreased after bFGF treatment. To determine if CST increase was linked to the proliferation of OL precursors induced by bFGF, cell proliferation was blocked by cytosine arabinoside (ARA-C). From 10(-8) to 10(-5) M ARA-C there was a dose-dependent inhibition of cell proliferation and a decrease in CST specific activity, whereas CNP specific activity was enhanced. When the cells were treated with bFGF and 10(-6) M ARA-C together, the proliferation was completely blocked and CST activity decreased by 72% below control values, whereas CNP activity was not significantly decreased. Immunocytochemical studies showed that the number of sulfatide-expressing cells and the number of cycling cells were increased after bFGF treatment, but that there was no overlapping between these two populations. Taken together these results suggest that CST activity and sulfatide expression appear shortly after the arrest of OL precursor division.

Regulation of cerebroside sulfotransferase activity in cultured oligodendrocytes: effect of growth factors and insulin

Cerebroside sulfotransferase (EC 2.8.2.11, CST) specific activity has been determined in oligodendrocyte (OL)-enriched glial cell cultures from newborn rat brain grown in serum supplemented medium. This activity is detectable at 5 days in vitro (DIV) and reaches its maximum value at 12 DIV. This period corresponds to that of oligodendrocyte precursor proliferation in these cultures. The activity decreases thereafter and remains nearly constant after 24 DIV. The developmental curve of CST activity is parallel in pure oligodendrocyte subcultures but twice higher than in primary cultures. These data confirm that CST is highly enriched in OL. Basic fibroblast growth factor (bFGF) (15 ng/ml) and platelet derived growth factor (PDGF) (0.75 U/ml) both enhance CST activity by 90% and 72%, respectively. This increase is in the same range than that of DNA content in treated cultures, whereas protein increase is smaller (50% and 22%, respectively). In contrast, transforming growth factor beta 1 (TGF beta 1, 0.5 and 5 ng/ml) does not significantly enhance CST activity nor DNA content of OL cultures. Insulin at high concentrations (5 micrograms/ml) also enhances CST activity but has no effect at physiological concentrations (20 ng/ml). These results show that CST activity can be controlled by growth factors. They suggest that CST activity is more closely related to OL and OL precursor proliferation than to myelination itself since its maximal activity preceeds myelination in vitro.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

2',3'-cyclic nucleotide 3'-phosphodiesterase and 5'-nucleotidase in the central nervous system of a myelin-deficient rat mutant

2',3'-Cyclic nucleotide 3'-phosphodiesterase activity was examined in brains and spinal cords of normal and myelin-deficient Wistar rats. While the activity in normal brains increased from 0.2 mumol/min/mg protein (units) at 6-10 days to 3.5 units at 25 days of postnatal age, the activity in the myelin-deficient rat remained at 0.2-0.3 units over the same period. In spinal cord, the normal activities were 5.7 and 10.9 units at 12 and 20 days, respectively, whereas they declined in the myelin-deficient rat from 1.06 to 0.79 units for the same age points. 5'-Nucleotidase activities in brain and spinal cord were normal in the myelin deficient rat at both ages.

Biochemical expression of mosaicism in female mice heterozygous for the jimpy gene

Expression of the jimpy gene in heterozygous females was analyzed by measuring galactolipid synthesis in brain during early myelination. Sulfatide labeling in brains of heterozygous females at 13-14 days is decreased to 40-80% that of female littermates who do not carry the jimpy gene. The activities of ceramide galactosyl transferase and cerebroside sulfotransferase and levels of myelin basic protein were similarly depressed. Since the jimpy gene was maintained with the Tabby gene in these studies, the effect of the Tabby gene on these parameters was examined and found to have no effect. These biochemical findings indicate that myelination is retarded in the brains of heterozygous jimpy females during the second week of development. However, at 18 days and thereafter, sulfatide labeling is less reduced, suggesting that the oligodendrocytes in brain attempt to compensate, in agreement with morphologic studies which show that myelin is decreased in brain during early development, but appears normal in adult animals.

Normal proliferation rate of galactocerebroside positive oligodendrocytes in brain cell cultures of the hypomyelinated mouse mutant jimpy

Proliferation of oligodendrocytes from the jimpy (jp) hypomyelinated mouse mutant was studied in dissociated brain cell cultures. This was done by combining anti-galactocerebroside (GC) immunostaining (for identifying oligodendrocytes) with [3H]thymidine autoradiography (for identifying proliferating cells). Previously we showed that the expression of GC in culture by jp oligodendrocytes is not altered by the jp mutation. Present results show that in 7-, 14- and 21-day-old jp cultures oligodendrocytes proliferate at a rate similar to that of normal GC+ oligodendrocytes. This indicates that, in jp brain cell cultures, oligodendrocytes which are not affected by mutation in their capability to express GC are also unaffected with regard to their proliferation rate.

The central-peripheral transition zone of cervical spinal nerve roots in Jimpy mutant and normal mice. Light- and electron-microscopic study

Comparative morphological and ultrastructural investigations on the cervical dorsal and ventral central-peripheral transition zones (CPTZs) of Jimpys and control mice have been performed at early and advanced myelination stages. After postnatal development a characteristic cone-shaped glial outgrowth extends into the proximal part of the dorsal roots, while the ventral roots exhibit short Schwann cell and peripheral nervous tissue invaginations into the spinal cord at the ventral root-spinal cord junction in both animal groups. In Jimpys, although there is marked central myelin deficiency and absence of oligodendroglial development on the CNS side, the normal general aspect of the CPTZs is maintained. Previously postulated astrocytic and neuroaxonal abnormalities in the mutants do not alter the central-peripheral borderline, and Schwann cell migration from the spinal nerve roots into the cord does not occur.

Developmental changes in glycolipid synthesizing enzymes in the brain of a myelin-deficient mutant Wistar rat

Changes in the activities of UDP-galactose:ceramide galactosyltransferase (CGalT, EC 2.4.1.45), UDP-glucose:ceramide glucosyltransferase (CGlcT, EC 2.4.1.80) and 3'-phosphoadenosine-5'-phosphosulfate (PAPS): galactosylceramide 3'-sulfotransferase (EC 2.8.2.11) over the myelinating period between 12 and 25 days were studied in the brains of control and myelin-deficient rats. Although the activity of galactosyltransferase with ceramides containing hydroxy fatty acids quadrupled in normal male littermates between 14 and 20 days, hardly any increase was observed in the mutant and the activity was less than 10% of control above 20 days of age. With normal fatty acid containing ceramides as acceptors, the activity decreased from 83% of the control at 12 days to approximately 30% after 20 days. Sulfotransferase activity also did not show the normal increase during the 3rd week of life and declined from 60% to 22%. Glucosyltransferase and lysosomal hydrolases in brain and ceramide galactosyltransferase in sciatic nerves appeared to be normal. These results suggest close similarities to the jimpy mutant mouse in which myelin deficiency is also inherited as an x-linked recessive trait.

Hypomyelinated mutant mice IV: peripheral myelin in jp msd

This study compares peripheral myelination in a specific subdivision of the sciatic nerve of jp msd and unaffected littermate mice. No significant differences are found in numbers of myelinated and unmyelinated axons, diameters of axons, thickness of myelin sheaths relative to axon diameter, extent of unmyelinated axons segregation by Schwann cell processes, or in the ultrastructure of myelin and Schwann cells. By contrast, jp msd mutant mice show severe CNS hypomyelination. This evidence, that the jp msd mutation affects only oligodendrocytes, distinguishes mutations at this locus from others producing CNS hypomyelination in which PNS myelin is also affected.

Levels and syntheses of cerebrosides and sulfatides in subcellular fractions of jimpy mutants

During the period of brain development, the levels of nonhydroxy- and hydroxycerebrosides in the cytosol from brains of jimpy mutants were determined by high-performance liquid chromatography and compared to those in the rest of the particulates from the same brains as well as those in the littermate controls. The concentrations of cerebrosides in jimpy brain preparations were much lower than in controls at all ages. In another experiment, [U-14C]glucose was injected intraperitoneally into jimpy mutants and their littermate controls. The amounts of radioactivity incorporated into cerebrosides and sulfatides in brain cytosol, the microsome-rich fraction, and the rest of the heavier particles were determined. Although the total radioactivity incorporated into these lipids was much lower in jimpy, the specific activities were 2-3 times the control value in all subcellular fractions.

Net sulfatide synthesis, galactosylceramide sulfotransferase and arylsulfatase A activity in the developing cerebrum and cerebellum of normal mice and myelin-deficient jimpy mice

Net sulfatide synthesis, galactosylceramide sulfotransferase (EC 2.8.2.11) and arylsulfatase A (EC 3.1.6.1) activities were measured in two brain regions, cerebrum and cerebellum, of normal and jimpy mice during postnatal development. In normally myelinating mice, two phases of increasing rates of net sulfatide synthesis were observed, the first coinciding with oligodendrocyte proliferation and the second with myelination. Net sulfatide synthesis was quantitatively higher in the cerebellum than in the cerebrum. In both brain regions, the developmental patterns of net sulfatide synthesis were related to the activity patterns of both galactosylceramide sulfotransferase and arylsulfatase A. In jimpy mice, a neurological mutant showing hypomyelination in brain, the first phase of net sulfatide synthesis was preserved in both brain regions and galactosylceramide sulfotransferase and arylsulfatase A activities were normal up to 12 days. However, during the phase in which myelination occurred in controls, the net sulfatide synthesis in both brain regions of jimpy mice was zero or even negative. The sulfatide deficit was larger in the cerebellum than in the cerebrum. In both mutant brain parts, galactosylceramide sulfotransferase activity increased up to 12 days showing about 50% of the maximal activities observed in normal brain regions. Thereafter up to 15 days, enzyme activity decreased to about 25% of that of controls and remained low in both brain regions. The developmental patterns and the activities of arylsulfatase A were, however, normal in the cerebrum and cerebellum of jimpy mice. These results suggest that the enzyme activities and the developmental patterns of galactosylceramide sulfotransferase and arylsulfatase A as measured in vitro reflect to a high degree their functional activity in vivo. Furthermore, sulfatide degradation by arylsulfatase A seems to be important in regulating net sulfatide synthesis during normal and impaired myelination.

A spin-label study of sciatic nerves from quaking, jimpy and trembler mice

The spin labels, 5-nitroxide stearic acid and 16-nitroxide stearic acid were incorporated into whole sciatic nerves dissected from normal, quaking, jimpy and trembler mice. With 5-nitroxide stearic acid, we have studied the thermal variation of the maximal apparent coupling constant (T) between 0 degrees C and 50 degrees C. Within this range of temperatures, we obtained identical values of 2 T for nerves from normal and jimpy mice, whereas 2 T was smaller for nerves from quaking and trembler mice. With 16-nitroxide stearic acid, composite spectra were recorded, particularly in the high-field range. A line characteristic of myelin was clearly observed in the spectra of nerves from normal and jimpy mice; its intensity was somewhat less in nerves from quaking mice and much less in spectra from trembler mice. A shoulder in the principal highfield line of the spectrum is modified only with nerves from jimpy mice. The results agree well with those obtained by electron microscopy, which reveal normal myelination in nerves from jimpy mice, a slight modification of the myelin from those of quaking mice and a practically complete demyelination in peripheral nerves from trembler mice. However, the structure of the nerves of jimpy mice also seems to be modified at an, as yet, undetermined level.

Diminished cerebroside-sulfotransferase activity in the Jimpy mouse mutant due to altered lipid composition in microsomal membranes

The mouse mutant Jimpy shows a deficient myelination. In the microsomes of the Jimpy brain, the cerebroside-sulfotransferase (EC 2.8.2.11) activity is low. The cerebroside-sulfotransferase activity of Jimpy microsomes could be normalised by delipidating the microsomes with cold acetone and adding to them acetone-extracted lipids from normal microsomes. The lipids extracted from Jimpy membranes did not influence the cerebroside-sulfotransferase activity of neither normal nor Jimpy microsomes. The same results were obtained if artificial cholesterol-phospholipid mixtures in ratios corresponding to the ones found in normal and Jimpy membranes were used for recombination experiments. Therefore the diminished enzyme activities in Jimpy microsomes may be related to the lower cholesterol-phospholipid ratio found in the microsomal membranes of the Jimpy mutant.

Dysmyelination of the central nervous system in the Chow-Chow dog

Five Chow-Chow dogs from three different litters had generalized body tremors since birth. Histologically a severe myelin deficiency was found in the central nervous system. The peripheral nerves were normally myelinated. Electron microscopically abnormally thin myelin sheaths and completely naked nerve fibers were found. There were many astrocytes in the myelin deficient areas as well as cells with the characteristic features of oligodendrocytes but also containing fibrils. The present cases are compared to other dysmyelinating diseases and possible pathogenetic mechanisms are discussed.

[Fatty acid distribution of the normal sciatic nerve lipids in the rat]

We isolated and purified the main lipids of the rat sciatic nerve. After methanolysis, fatty acids were isolated and purified by thin layer chromatography, and studied by gas chromatography. C 16 and C 18 fatty acids are the most abundant. Among the long-chain fatty acids, arachidonic acid (20:4) is present in some lipids; highly desaturated fatty acids in C 22 and C 24 are also present. In general, the fatty acids are highly saturated; cholesterol esters and ethanolamine phosphoglyceride fatty acids are highly unsaturated.

3'-phosphoadenylylsulfate:galactosylceramide 3'-sulfotransferase. An optimized assay in homogenates of developing brain

An optimized in vitro assay of 3'-phosphoadenylysulfate:galactosylceramide 3'-sulfotransferase (EC 2.8.2.11, galactosylceramide sulfotransferase, formerly known as galactocerebroside sulfotransferase) activity is presented, that can be used in crude homogenate of brain tissue of various developmental stages. The enzyme activity is determined by measuring the [35S]sulfatides formed by the enzymic transfer of [35S]sulfate from 3'-phosphoadenoside 5'-phospho [35S]sulfate to galactosylceramides. The sulfatide formation at 30 degrees C is linear up to 30 min and up to a protein concentration of 1 mg per 0.5 ml assay volume. The presence of 0.4% Triton X-100 and 50 micrometer exogenous bovine cerebrosides are optimal for enzyme activity. The pH optimum of the reaction is at pH 6.5 using 0.1 M imidazole buffer. The enzyme reaction is stimulated by NaCl, KCl, MgCl2, CaCl2, MnCl2, ATP and inhibited by ADP. The developmental enzyme activity pattern of mouse brain is the same, if derived from homogenates and microsomes, respectively, under our assay conditions.