[Some ultrastructural aspects of white matter in Quaking mice]

The QKI-6 and QKI-7 RNA binding proteins block proliferation and promote Schwann cell myelination

Background

The quaking viable (qk^v) mice have uncompacted myelin in their central and peripheral nervous system (CNS, PNS). The qk gene encodes 3 major alternatively spliced isoforms that contain unique sequence at their C-terminus dictating their cellular localization. QKI-5 is a nuclear isoform, whereas QKI-6 and QKI-7 are cytoplasmic isoforms. The qk^v mice harbor an enhancer/promoter deletion that prevents the expression of isoforms QKI-6 and QKI-7 in myelinating cells resulting in a dysmyelination phenotype. It was shown that QKI regulates the differentiation of oligodendrocytes, the myelinating cells of the CNS, however, little is known about the role of the QKI proteins, or RNA binding proteins in PNS myelination.

Methodology/Principal Findings

To define the role of the QKI proteins in PNS myelination, we ectopically expressed QKI-6 and QKI-7 in primary rat Schwann cell/neuron from dorsal root ganglia cocultures. We show that the QKI isoforms blocked proliferation and promoted Schwann cell differentiation and myelination. In addition, these events were coordinated with elevated proteins levels of p27^KIP1 and myelin basic protein (MBP), markers of Schwann cell differentiation. QKI-6 and QKI-7 expressing co-cultures contained myelinated fibers that had directionality and contained significantly thicker myelin, as assessed by electron microscopy. Moreover, QKI-deficient Schwann cells had reduced levels of MBP, p27^KIP1 and Krox-20 mRNAs, as assessed by quantitative RT-PCR.

Conclusions/Significance

Our findings suggest that the QKI-6 and QKI-7 RNA binding proteins are positive regulators of PNS myelination and show that the QKI RNA binding proteins play a key role in Schwann cell differentiation and myelination.

Abnormal postnatal ontogeny of the locus coeruleus in the epileptic mutant mouse quaking

The tonic-clonic convulsions of the quaking mutant mice have been shown to be associated with the hyperplasia of the nucleus locus coeruleus, the origin of most brain noradrenergic neurons. In the present study, the postnatal ontogeny of the locus coeruleus has been studied by tyrosine hydroxylase immunolabeling in the mutant mice quaking and their controls at postnatal days 1, 30 and 90. In the control mice, the number of immunoreactive neuronal cell bodies increased significantly in the rostral half of the locus coeruleus between birth and postnatal day 30, while it decreased significantly in the caudal half between birth and adulthood. Thus, during postnatal maturation, the distribution of locus coeruleus neurons was shifted in the rostral direction. In the quaking mutant mice, while the increase of immunolabeling between birth and postnatal day 30 was observed in the rostral half of the locus coeruleus, no diminution could be found in the caudal half between birth and adulthood. As a result, the rostral shift of tyrosine hydroxylase immunoreactivity was not observed. Consequently, in adult mice, the caudal part of the mutants locus coeruleus appeared to contain significantly more neurons than the corresponding region in the controls. These results indicate that the hyperplasia of the locus coeruleus of the quaking mice that we had previously reported results from an alteration of the postnatal maturation of this nucleus. This developmental abnormality might be a primary determinant of the inherited epilepsy of the quaking mutant mice.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Cerebellar soluble lectin and its glycoprotein ligands in the developing brain of control and dysmyelinating mutant mice

The levels of an endogenous lectin, the cerebellar soluble lectin (CSL) and of its endogenous glycoprotein ligands were studied using immunoblotting and affinoblotting techniques in the forebrain of quaking, shiverer and jimpy dysmyelinating mutant mice and their respective control littermates during the postnatal development. In the controls of the mutant mice, the level of CSL showed an important increase between days 5-18 then a stabilization, although at all ages the level of CSL was reduced (at least 15%) in the control littermate of the shiverer mutant. In the shiverer mutant the developmental pattern is similar to the control but was reduced by 50% as compared to the control. In the jimpy mutant an erratic development of CSL was observed which was with quasi absence of CSL at days 12 and 25. Variation of CSL levels in the quaking brain were also observed. CSL glycoprotein ligands also showed variable developmental profiles with a special persistence with ageing of CSL-binding glycoproteins in the quaking and jimpy mice. Developmental variations were also observed between the different control littermates. These results are discussed in view of developmental roles attributed to CSL and its glycoproteins ligands in cell adhesion mechanism during brain ontogenesis and especially myelination.

Quaking shiverer double mutant mice: morphological phenotypes support possible dual actions of the shiverer locus

Mice doubly homozygous for the two different hypomyelination mutations, quaking (qk) and shiverer (shi) or shiverer myelin-deficient (shimld) (abbreviations: qk*shi and qk*shimld), both have much less myelin than either single mutant ancestor, myelin morphology resembling shi or shimld rather than qk, and abundant shi-type oligodendrocytic microprocesses. The qk*shimld double mutant differs from qk*shi only in having small amounts of normal or abnormal major dense line, in keeping with the morphologic difference between the shi and shimld single mutants. By contrast, shi*jp and shimld*jp have clearly different morphological phenotypes; unexpectedly the major dense line is present in the CNS myelin of shi*jp but not shimld*jp. When shi and shimld act alone, their different DNA abnormalities produce similar protein abnormalities. We speculate that the two mutations interact with qk at a different, later step of DNA expression than they interact with jp. In the interaction with qk, the similar proteins produce similar morphologies. In the interaction with jp, the different DNAs are somehow caused to produce protein differences that are reflected in different morphologies. In this study we have observed for the first time a morphological effect of these mutant genes in heterozygous animals. Of particular importance, animals whose genomes combine shi/+ or shimld/+ with qk/qk produce qk-type, compacted myelin but abundant shi-type oligodendrocyte microprocesses. We consider this as evidence that both shi and shimld have two effects: non-production of a normal structural protein, myelin basic protein, and production of an abnormal protein which perturbs the cytogogic function we postulate to be normally exercised by the myelin basic protein gene.

Acylgalactosylceramides in developing dysmyelinating mutant mice

Acylgalactosylceramides (AGC) from forebrains of normal and dysmyelinating (quaking and shiverer) mice were purified by Florisil column chromatography and preparative TLC. These procedures resolved the AGC on the basis of their Rf values into two main fractions which comigrate with their homologs from rat forebrains. In control animals, AGC were detectable in mouse forebrains from the eighth postnatal day and reached maximal values within 20 days. The same developmental pattern was obtained in dysmyelinating shiverer mice but the AGC content was reduced to approximately 30% of control values. In quaking mutants, the AGC were hardly detected. They were also present in sciatic nerve of normal mice and to a lesser extent in trembler mice. Gas chromatography-mass spectrometry analysis of both ester- and amide-linked fatty acids isolated from AGC of normal and shiverer mice shows that the shiverer mutant AGC display a chemical structure similar to that of normal AGC. AGC constituents of control myelin are reduced by approximately 70% in shiverer myelin, indicating that these molecules can be considered as early markers of oligodendrocyte differentiation. The early arrest of myelinogenesis in the quaking animals and the near absence of AGC are in good agreement with this proposal. Moreover, the reduced amount of AGC in the trembler PNS indicates that AGC could also be early markers for differentiation of the Schwann cell.

Growth cones, dying axons, and developmental fluctuations in the fiber population of the cat's optic nerve

We have studied the rise and fall in the number of axons in the optic nerve of fetal and neonatal cats in relation to changes in the ultrastructure of fibers, and in particular, to the characteristics and spatiotemporal distribution of growth cones and necrotic axons. Axons of retinal ganglion cells start to grow through the optic nerve on the 19th day of embryonic development (E-19). As early as E-23 there are 8,000 fibers in the nerve close to the eye. Fibers are added to the nerve at a rate of approximately 50,000 per day from E-28 until E-39--the age at which the peak population of 600,000-700,000 axons is reached. Thereafter, the number decreases rapidly: About 400,000 axons are lost between E-39 and E-53. In contrast, from E-56 until the second week after birth the number of axons decreases at a slow rate. Even as late as postnatal day 12 (P-12) the nerve contains an excess of up to 100,000 fibers. The final number of fibers--140,000-165,000--is reached by the sixth week after birth. Growth cones of retinal ganglion cells are present in the optic nerve from E-19 until E-39. At E-19 and E-23 they have comparatively simple shapes but in older fetuses they are larger and their shapes are more elaborate. As early as E-28 many growth cones have lamellipodia that extend outward from the core region as far as 10 microns. These sheetlike processes are insinuated between bundles of axons and commonly contact 10 to 20 neighboring fibers in single transverse sections. At E-28 growth cones make up 2.0% of the fiber population; at E-33 they make up about 1.0%; from E-36 to E-39 they make up only 0.3% of the population. Virtually none are present in the midorbital part of the nerve on or after E-44. At all ages growth cones are more common at the periphery of the nerve than at its center. This central-to-peripheral gradient increases with age: at E-28 the density of growth cones is two times greater at the edge than at the center but by E-39 the density is four to five times greater. Necrotic fibers are observed as early as E-28 in all parts of the nerve. Their axoplasm is dark and mottled and often contains dense vesiculated structures.(ABSTRACT TRUNCATED AT 400 WORDS)

Altered postnatal ontogeny of alpha 1- and alpha 2-adrenoceptor binding sites in the brain of a convulsive mutant mouse (quaking)

Binding assays of [3H]dihydroalprenolol ([3H]DHA), [3H]prazosin and [3H]clonidine have been performed on whole brain (minus cerebellum) homogenates of the convulsive mutant mice quaking (qk) and the controls of the same strain (C57BL/6J:B6). In 70-day-old mutants (which fully exhibit the qk convulsive phenotype), the binding of [3H]DHA to beta-adrenoceptor binding sites was not different from the controls, whereas the binding capacities of [3H]prazosin and [3H]clonidine to alpha 1-and alpha 2-adrenoceptor sites, respectively, were greatly enhanced. The biphasic ontogenic pattern of alpha 2-adrenoceptors had a greater amplitude in the brain of 30- to 90-day-old mutants than in the corresponding B6 controls. In mutants younger than 30 days or older than 90 days, the number of alpha 2-adrenoceptor sites was not modified. The number of alpha 1-adrenoceptor binding sites was increased in the brain of the mutants, only in animals older than 70 days. In younger mice, the postnatal modulation of alpha 1-adrenoceptor sites was identical to the controls. Regional studies were performed in 70-day-old mice. [3H]clonidine binding was increased in the brainstem of the mutants, and to a lesser extent in the cerebral cortex, while it was slightly diminished in the hypothalamic area. [3H]prazosin binding was also increased in the brainstem of the mutants, and decreased in the olfactory bulbs. Our results suggest that the convulsions of the qk mutants are selectively associated with modifications of alpha- and not beta-adrenoceptor binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain gangliosides of quaking and shiverer mutants: qualitative and quantitative changes of monosialogangliosides in the quaking brain

Ganglioside compositions in the brains of the mutant mice quaking and shiverer were compared with those of their littermate controls, C57BL/6 and C3HSWV. Neither ganglioside content nor composition of shiverer brains differed from those of the control brains. Change in the ganglioside composition of the mutant brain from that of the control was observed only in the quaking mutant brain, in which monosialoganglioside GM1 was significantly reduced and GM4 was completely absent. The structures of the gangliosides were determined by negative ion fast atom bombardment mass spectrometry, and the GM3 and GM4 gangliosides in the quaking brain were found to be altered in regard to their long-chain base and fatty acid compositions when compared to the normal C57BL/6 brain.

A quantitative assessment of myelin sheaths in the peripheral nerves of dystrophic, quaking, and trembler mutants

If myelin sheaths are relatively thin for axon caliber, this is generally taken as a sign of insufficient myelin formation. However, recent studies have shown that sheath thickness relates not only to axon caliber; the relative length of the internode is also important. Foreshortened internodes have slightly thinner sheaths than long internodes of the same fiber caliber (Friede and Bischhausen 1982). In the present study we compared sheath thickness with internode geometry in the sciatic fibers of three murine mutants, the Dystrophic, Quaking and Trembler mice, using a new computer-assisted method. A quantitative correspondence was found between abnormally thin sheaths and internode foreshortening. The magnitude of the changes was the same as that found previously in normal and regenerated fiber populations. The data show that the geometric proportions of internodes cannot be ignored when assessing sheath thickness, and they also shed some new light on the mechanisms which produce abnormally thin sheaths.

Axonal swellings in jimpy mice: does lack of myelin cause neuronal abnormalities?

We have observed focal axonal enlargements in jimpy, a myelin deficient mutant mouse. Similar axonal swellings have also been found in other studies, in two other myelin deficient mutant mice and in a myelin deficient mutant rat. We suggest that this axonal abnormality represents a common secondary reaction to lack of myelin. Such a secondary reaction might also occur in other species including human, in response to deficient myelin or to loss of myelin due to disease.

Altered brain copper and zinc content in quaking mice

Brain copper and zinc levels were determined in 21-day-old and "adult" C3HeB/FeJ quaking mice and in normal littermate controls. Expressed per gram dry weight of brain, copper was increased 84% over normal mice at 21 days after birth, but was not significantly different from normal in the adults. Zinc was increased 23 to 24% at both ages. At both ages, brains from quaking mice had a significantly reduced content of solids, indicating increased water content in the mutant brain. Our study is the first to report copper and zinc content as a measure of both wet and dry brain weights. Our results indicate abnormal copper content in the quaking mutant. The relationship between copper content and other aspects of the quaking phenotype, including its seizure behavior and myelin deficit, remain to be established.

Quaking mouse: vacuolar degeneration of spinal roots

Quaking is a neurologic mutant mouse with hypomyelination of CNS and PNS. In this mutant mouse of over 6 months of age, extensive vacuolation was found in the nerve fibers of the spinal roots, mostly in the ventral root. Normal axoplasmic constituents, such as mitochondria, neurotubules, and neurofilaments were, in general, well preserved. Many of these vacuoles appeared to be intra-axonal and only a few showed direct continuity with dilated periaxonal space. However, moderately electron-dense fluffy materials were often found in both the vacuoles and in the dilated periaxonal space, and rare mononuclear cells were found within the vacuoles, suggesting that these vacuoles were likely to be dilated periaxonal spaces. The vacuoles tended to be found more often in the myelinated nerve fibers than non-myelinated fibers. The changes in the periaxonal spaces observed in the old quaking mice were closely similar to those found in the myelinated cultures maintained on low calcium medium (Blank et al. 1974). Since calcium is highly concentrated in the node-paranodal regions and may be involved in the adhesion of Schwann cell loops to the axolemma (Ellisman et al. 1979), disturbed calcium and possibly other ionic concentrations due to structural abnormalities of node and paranodal regions in quaking mouse (Suzuki and Zagoren 1977) are speculated to be responsible for such morphological changes of spinal root in this mutant mouse.

Triethyl tin does not induce intramyelinic vacuoles in the cns of the quaking mouse

Triethyl tin (TET), when injected intraperitoneally, failed to produce the typical intramyelinic edema in the spinal cord of quaking mice with two different genetic backgrounds (B6C3H-qk and BTBRTF/Nev-qk), while control littermates and normal C57BL/6J mice were susceptible, as expected. The only prominent change in the quaking mice was the presence of spherical vacuoles containing floccular electron-dense materials, some of which were clearly within the oligodendroglial perikarya and the inner and outer tongues. They are likely to represent degenerative responses. Consistent with the lack of edema, no increase in the water content was found in the quaking spinal cord following TET injection. Although the presence of numerous interlamellar tight junctions in quaking CNS myelin may mechanically restrict formation of the intralamellar vacuoles, the unique changes in the oligodendroglia and the lack of edema fluid accumulation suggest more fundamental metabolic abnormality that renders the quaking CNS resistant to the triethyl tin-induced edema.

Resistance of quaking mouse CNS to triethyl tin edema

Intraperitoneal injection of triethyl tin (TET) sulfate, 5 or 10 mg/kg body weight did not induce intramyelinic edema without altering water content in quaking mice while in C57BL/6J and littermate control mice, water content was increased and typical intramyelinic edema was induced following TET injection. Even among control mice, however, there were some strain differences in the histological severity of the edema, which were in precise agreement with the quantitative alterations in water content. These observations suggest that CNS myelin in quaking may differ qualitatively from that in controls and the mode of response to TET is under genetic control.

Radial component of central myelin in normal and quaking mice

Radial component of myelin sheaths was investigated in C57BL and quaking mice. In immature myelinated fibres of C57BL mice, more than one group of radial component were observed in the several regions of myelin sheaths while in mature fibres, one group of radial component was localized between the internal mesaxon and outer tongue process which were situated within 90 degrees of each other. In thinly myelinated fibres of adult quaking mice, numerous groups of radial component were found at random distance and directions but they were always closely related to the cytoplasmic islands of oligodendroglia. Even in quaking mice, small well myelinated fibres showed normal mature pattern of radial component. Possible functional significance of radial component was briefly discussed.

Chronological study of oligodendroglial alterations and myelination in quaking mice

Chronological morphological investigation was carried out in the spinal cord of quaking mice from day 3 to day 130. Numbers of myelinated fibres were far fewer in quaking mice at day 3 compared to controls. However, when the animals became older, myelination progressed and numbers of myelinated fibres increased although myelin sheaths remained far thinner than the size of axons. Many oligodendroglia during day 5 to 15 in quaking mice revealed prominent dilation and proliferation of smooth walled vesicles and cisterns but after 20 days, such changes were no longer observed. Tortuous bizarre oligodendroglial processes, aberrant myelination and myelin figures were very prominent around day 5--15, but such changes also gradually subsided. Density of glial cells during pre-myelination gliosis was similar in both quaking and control mice. However, glial cell population decreased far slower pace than controls when myelination progressed. Thus, glial cell density remained proportionally higher in quaking than controls although the density declined with age in both.

Regional distribution of myelin basic protein in the central nervous system of quaking, jimpy, and normal mice during development and aging

Myelin basic protein (MBP) was quantified using a RIA technique in the spinal cord, cerebellum, diencephalon plus brainstem region and cerebral hemispheres of two dysmyelinating murine mutants, quaking (qk) and jimpy (jp) mice. Comparison was made with normal control values. The whole life-span has been investigated: ie, ages ranging from 0 to 26 days for the jp, O to one year for the qk, and prenatal stage to three years for the control animals. Assays in the mutants at early ages were rendered feasible by the use of marker genes, which has allowed the diagnosis of the mutation at birth, 12 days before the expression of their typical tremor phenotype. Special care was given to the period of early myelinogenesis in order to clarify the dysynchrony between the various parts of the central nervous system. In normal mice, MBP was already detected in the brain of 19-day-old embryos. During development, rapid accumulation of MBP first occurred in the spinal cord then in the diencephalon, the brainstem, the cerebellum, and finally in the cerebral hemispheres. In the 25-day-old jimpy mutant, levels of MBP were found dramatically decreased, never exceeding 6% of the normal controls in any of the areas investigated. The situation for the quaking mouse was quite different. This mutant could be investigated up to one year old. At that age, a high discrepancy was observed between the values found in the brain and in the spinal cord (respectively, 10% and 35%) compared to normal controls. In both mutants, not only were the levels of MBP decreased, but also its appearance during development was delayed. Nevertheless, in both mutants the caudo-rostral timing of myelination as assayed by MBP levels was maintained. Furthermore, the later myelination occurred, the stronger weas the deficit in MBP. Interestingly, in the quaking mutant, the specific plasticity of the spinal cord was exemplified by its ability to reduce constantly, even at an advanced age, its initial deficit of MBP.

Brain nucleic acids and protein in various neurological mutant mice

A study was made to compare alterations in the cerebral contents of nucleic acids and protein of several mouse strains affected by different neurological mutations: jimpy, msd, quaking, reeler, weaver, and dwarf. In normal and affected jimpy and msd mice the brain components analyzed were very similar. On the other hand, the cerebral hemispheres of quaking mice showed significant decreases in total RNA and DNA, when compared with those of normal littermates. In the affected reeler and weaver mice, total protein, RNA, and DNA in the cerebellum differed markedly from controls. Protein decreased slightly, whereas nucleic acids showed no significant variation in the cerebral hemispheres of the same mutants. The cerebella and cerebral hemispheres of affected dwarf mice had wet weights and total protein contents that were about 20% lower than those of their controls; DNA did not vary significantly in the various brain regions analyzed. The decrease of DNA we report in reeler and weaver mutant cerebellum in toto quantifies the lack of cell number, in contrast to histological studies which give only semiquantitative information.

Accumulation of GFA, the monomeric precursor of the gliofilaments, during development in normal mice and dysmyelinating mutants

Astrocytic reactivity during the myelination period in the mouse was studied with immunochemical method, ie, quantitative determination of the soluble pool of the GFA protein. There is normally a maximum content at the time of early myelinogenesis in any structure; then the GFA level decreases and finally keeps constant for a long period during the adult life. This evolutive pattern is also observed in the dysmyelinating mutant quaking, with a permanent shift toward higher values especially in areas of earlier maturation. In the jimpy mutant, practically devoid of myelin, the increase of GFA occurs but does not stop until death, at 25 days postnatal. This study points out 1) the capacity of astrocytes to synthesize surprisingly high amounts of soluble GFA at periods of intense metabolic activity, and 2) the reactivity of astrocytes in relation to the degree of deficiency of the myelinating oligodendrocytes.

Immunohistochemical localization of the myelin basic protein and of the glial fibrillary acidic protein: comparative study in normal, quaking and jimpy mice

The topographical distribution of myelin basic protein (MBP) and of glial fibrillary acidic protein (GFA) have been compared in the CNS of 18-day-old normal, quaking, and jimpy mice using indirect immunofluorescence. Comparison was made in brain and spinal cord sections. MBP was strongly decreased in quaking and jimpy mice in all parts of the CNS. A pronounced gliosis was observed in jimpy mice with occurrence of numerous hypertrophied astrocytes. To a lesser extent, an astrocytic reaction was also observed in quaking CNS.

Absence of the major dense line in myelin of the mutant mouse "shiverer"

The myelin of the central nervous system (CNS) of the mutant mouse Shiverer is characterized by the absence of the major dense line (MDL). The intraperiod line, as seen in conventional electron micrographs and in freeze-fractured replicas, appears normal. Peripheral myelin, as seen in ventral and dorsal roots of spinal cord, is unaffected by the mutation. During the period of active myelination, the cytoplasm of most oligodendrocytes (ODs) is packed with electron-lucent vacuoles in continuity with the Golgi apparatus and with bundles of microtubules. It is concluded that a metabolic pathway possibly involving the Golgi apparatus, and contributing to the formation of the MDL is selectively affected in this mutant.

In vivo incorporation of 32P into myelin basic protein from normal and quaking mice

Myelin basic protein in normal mice is phosphorylated. Since phosphorylation can decrease the net positive charge of the myelin basic protein, this could affect molecular interactions between this protein and other myelin components. In this study 32P incorporation into small and large components of the myelin basic protein was studied in immature and young adult mice and also in Quaking mutants which have a severe myelin deficit. We found a short half-life of 32P in myelin basic protein. The 32P specific activity of myelin basic protein was higher in immature and Quaking mice than in young adult animals. Of the 32P-labeled basic proteins of control and Quaking mice, the small component had a slightly higher specific activity than the large component. Although the small basic protein is quantitatively decreased in Quaking mice, the ratio of specific activity of small to large basic protein is similar in control and Quaking animals. Since Quaking and immature mice have many uncompacted myelin lamellae, these preliminary results suggest that phosphorylation and dephosphorylation could be involved in compaction mechanisms.

Immunohistochemical studies of Wolfgram proteins in central nervous system of neurological mutant mice

Immunohistochemical localization of Wolfgram proteins has been studied by the indirect immunoperoxidase technique with Wolfgram protein W1 antibodies in the nervous system of myelin deficient mutant mice: Jimpy, MSD and Quaking. In all these mutants, the myelinated fibers and the oligodendroglial cells (few in number) in the corpus callosum and the white matter of the cerebellum folium show a positive reaction to protein W1. These observations are in accordance with the immunological studies showing that the two major Wolfgram proteins, W1 and W2, of mutant mice have immunological similarities with that of the controls.

Quaking mouse: an ultrastructural study of the peripheral nerves

Ultrastructural study of the peripheral nervous system of quaking mice has revealed several unusual features in the pattern of myelination in addition to hypomyelination. These are 1) the presence of 'atypical' Schmidt-Lanterman incisures, 2) irregularities of the nodal and internodal termination of Schwann cell cytoplasm and 3) the presence of non-myelinated segments without associated Schwann cell processes, but covered by basal lamina. In view of the observation of similar features during the development of the P.N.S. and also during P.N.S. remyelination, we suggest that these features are the results of modified myelination due to a defect in the control mechanisms necessary for normal myelination.

Evidence for defective incorporation of proteins in myelin of the quaking mutant mouse

The defect in myelinogenesis present in the Quaking mutant mouse was investigated using a double radioisotope technique for comparing the incorporation of amino acid into myelin proteins of normal and mutant mice. Quaking mice and littermate controls received intracranial injections of 150 muCi [3H]glycine and 25 muCi of [14C]glycine respectively. After 2 h their brains were combined and jointly processed to obtain subcellular fractions. The 3H/14C ratio for the myelin subfraction was 1.88 as compared to a 3H/14C ratio of 3.0 for the other subfractions, indicating a 40% decrease in glycine incorporation into myelin of Quaking mice. Myelin proteins were separated by discontinuous gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) and the 3H/14C ratios determined in each gel slice. In contrast to the microsomal subfractions which gave a 3H/14C ratio of 2.6 across the gel, the 3H/14C ratio of myelin showed large variations with values ranging from 0.54 for proteolipid protein to 2.0 for some of the high molecular weight proteins. During development, the Quaking mutant exhibited a preferential depression in glycine incorporation into proteolipid protein in 18-day-old mice, while in older animals (32-54 days) the fast migrating basic protein, as well as the proteolipid protein, was labeled to a significantly lesser extent.

Hyperplasia of oligodendrocytes in quaking mice

The number of neuroglial cells in selected fiber tracts of 90-day-old quaking and normal mice was determined by a combination of light and electron microscopy. Oligodendrocytes of quaking mice are normal in number in the anterior commissure and corticospinal tract (in the cervical spinal cord) but are increased two- to fourfold in the optic nerve and the fasciculi cuneatus and gracilis (in the cervical spinal cord). The nuclei and perikarya are normal in size or smaller than normal. Those tracts with the greatest hyperplasia of oligodendrocytes also have the greatest content of myelin, suggesting that cell number influences content of myelin. However, the volume of myelin per oligodendrocyte also varies, between 2 and 11% of normal, in the different tracts of the mutant. The hyperplasia of oligodendrocytes in quaking mice may arise as compensation for their decreased production of myelin and reflect a normal plasticity in the processes of myelination. If so, the mutant may be a useful system for study of the regulation of myelogenesis.

Alterations in the accumulation patterns of polyamines in brains of myelin-deficient mice

Quaking mutants and jimpy mutants of mice have known deficiencies of myelination of the central nervous system, as well as lesser involvement of the peripheral nervous system. Both mutants also have altered polyamine synthesis and accumulation, particularly in the hindbrain and spinal column. The ratio of spermidine/spermine, which generally is higher in tissues with high rates of biosynthetic activity, was significantly lower in the mutants as compared to their normal siblings. In quaking mutants, 5 months of age, the spermidine concentration of hindbrain and spinal column was 60% that of controls. In contrast, the decreased spermidine/spermine ratio in jimpy mutants resulted from a marked increase in the spermine concentration in both forebrain and hindbrain. Alterations in the spermidine/spermine ratio could lead to reductions in the biosynthetic potential of the brain during development.