Aluminum inhibits neurofilament protein degradation by multiple cytoskeleton-associated proteases

Intense Pulsed Electric Fields Denature Urease Protein

Background: This article describes the effects of nanosecond pulsed electric fields (nsPEFs) on the structure and enzyme activity of three types of proteins. Materials and Methods: Intense (up to 300 kV/cm) 5-ns-long electrical pulses were applied for 500 times at 3 Hz to solutions of lysozyme, albumin, and urease. We analyzed covalent bonds (peptide bonds and disulfide bonds) of lysozyme and albumin, and also the tertiary and quaternary structures of urease as well as urease activity. Results: The results indicated deformation of both the quaternary and tertiary structures of urease upon exposure to an electric field with an amplitude of 250 kV/cm or higher, whereas no structural changes were observed in lysozyme or albumin, even at 300 kV/cm. The enzyme activity of urease also decreased at field strengths of 250 kV/cm or higher. Conclusion: Our experiments demonstrated that intense nsPEFs physically affected the conformation and function of some types of proteins. Such intense electric fields often occur in cell membranes when exposed to a moderate pulsed electric field.

Aluminum induces neurofilament aggregation by stabilizing cross-bridging of phosphorylated c-terminal sidearms

Exposure to neurotoxin aluminum neurotoxicity is accompanied by the perikaryal accumulation of tangles of phosphorylated neurofilaments (NFs). We examined their formation and reversibility under cell-free conditions. AlCl3 induced dose-dependent formation of NF aggregates, ultimately incorporating 100% of detectable NFs. The same concentration of CaCl2 induced approximately 25% of NFs to form longitudinal dimers and did not induce aggregation. AlCl3 induced similar percentages of aggregates in the presence or absence of CaCl2, and CaCl2 could not reduce pre-formed aggregates. CaCl(2)-induced dimers and AlCl(3)-induced aggregates were prevented by prior NF dephosphorylation. While CaCl(2)-induced dimers were dissociated by phosphatase treatment, AlCl(3)-induced aggregates were only reduced by approximately 50%, suggesting that aggregates may sequester phosphorylation sites. Since phosphatases regulate NF phosphorylation within perikarya, inhibition of NF dephosphorylation by aluminum would promote perikaryal NF phosphorylation and foster precocious phospho-dependent NF-NF associations. These findings are consistent with the notion that prolonged interactions induced among phospho-NFs by the trivalent aluminum impairs axonal transport and promotes perikaryal aggregation.

Neuronal intermediate filaments and neurodegenerative disorders

Intermediate filaments represent the most abundant cytoskeletal element in mature neurons. Mutations and/or accumulations of neuronal intermediate filament proteins are frequently observed in several human neurodegenerative disorders. Although it is now admitted that disorganization of the neurofilament network may be directly involved in neurodegeneration, certain type of perikaryal intermediate filament aggregates confer protection in motor neuron disease. The use of various mouse models provided a better knowledge of the role played by the disorganization of intermediate filaments in the pathogenesis of neurodegenerative disorders, but the mechanisms leading to the formation of these aggregates remain elusive. Here, we will review some neurodegenerative diseases involving intermediate filaments abnormalities and possible mechanisms susceptible to provoke them.

The predominant form in which neurofilament subunits undergo axonal transport varies during axonal initiation, elongation, and maturation

The forms in which neurofilament (NF) subunits undergo axonal transport is controversial. Recent studies from have provided real-time visualization of the slow axonal transport of NF subunits by transfecting neuronal cultures with constructs encoding green fluorescent protein (GFP)-conjugated NF-M subunits. In our studies in differentiated NB2a/d1 cells, the majority NF subunits underwent transport in the form of punctate NF precursors, while studies in cultured neurons have demonstrated transport of NF subunits in predominantly filamentous form. Although different constructs were used in these studies, transfection of the same cultured neurons with our construct yielded the filamentous pattern observed by others, while transfection of our cultures with their construct generated punctate structures, confirming that the observed differences did not reflect variances in assembly-competence among the constructs. Manipulation of intracellular kinase, phosphatase, and protease activities shifted the predominant form of GFP-conjugated subunits between punctate and filamentous, confirming, as shown previously for vimentin, that punctate structures represent precursors for intermediate filament formation. Since these prior studies were conducted at markedly differing neuronal differentiation states, we tested the alternate hypothesis that these differing results reflected developmental alterations in NF dynamics that accompany various stages of neuritogenesis. We conducted time-course analyses of transfected NB2a/d1 cells, including monitoring of transfected cells over several days, as well as transfecting cells at varying intervals prior to and following induction of differentiation and axonal neurite outgrowth. GFP-conjugated subunits were predominantly filamentous during the period of most robust axonal outgrowth and NF accumulation, and presented a mixed profile of punctate and filamentous forms prior to neuritogenesis and following the developmental slowing of neurite outgrowth. These analyses demonstrate that NF subunits are capable of undergoing axonal transport in multiple forms, and that the predominant form in which NF subunits undergo axonal transport varies in accord with the rate of axonal elongation and accumulation of NFs within developing axons.

Ligand specific effects on aluminum incorporation and toxicity in neurons and astrocytes

Aluminum is present in many manufactured foods and medicines and is added to drinking water for purification purposes. It has been proposed that aluminum is a contributing factors to several neurodegenerative disorders such as Alzheimer's disease. However, this remains controversial primarily due to the unusual properties of aluminum and a lack of information on its cellular sites of action. To resolve some of these questions, we have examined aluminum uptake in both neuronal and astroglial cells as well as the role of metal speciation. The relative accumulation of four aluminum salts, aluminum maltolate, aluminum lactate, aluminum chloride and aluminum fluoride, was investigated and correlated with cell viability and intracellular distribution as determined by morin staining. Significant differences in aluminum incorporation and toxicity were observed in both neuronal and glia cells with the largest effects exhibited by the maltol species. This was accompanied by a nuclear accumulation in the neuronal cell line that was contrasted by the perinuclear, vesicular distribution in astrocytes that partially co-localized with cathepsin D, a lysosomal marker. These findings demonstrate differences in aluminum species and highlights the importance of these factors in modulating the toxic effect of aluminum.

Alterations in the cytoskeleton accompany aluminum-induced growth inhibition and morphological changes in primary roots of maize

Although Al is one of the major factors limiting crop production, the mechanisms of toxicity remain unknown. The growth inhibition and swelling of roots associated with Al exposure suggest that the cytoskeleton may be a target of Al toxicity. Using indirect immunofluorescence microscopy, microtubules and microfilaments in maize (Zea mays L.) roots were visualized and changes in their organization and stability correlated with the symptoms of Al toxicity. Growth studies showed that the site of Al toxicity was associated with the elongation zone. Within this region, Al resulted in a reorganization of microtubules in the inner cortex. However, the orientation of microtubules in the outer cortex and epidermis remained unchanged even after chronic symptoms of toxicity were manifest. Auxin-induced reorientation and cold-induced depolymerization of microtubules in the outer cortex were blocked by Al pretreatment. These results suggest that Al increased the stability of microtubules in these cells. The stabilizing effect of Al in the outer cortex coincided with growth inhibition. Reoriented microfilaments were also observed in Al-treated roots, and Al pretreatment minimized cytochalasin B-induced microfilament fragmentation. These data show that reorganization and stabilization of the cytoskeleton are closely associated with Al toxicity in maize roots.

Aluminum inhibits neurofilament assembly, cytoskeletal incorporation, and axonal transport. Dynamic nature of aluminum-induced perikaryal neurofilament accumulations as revealed by subunit turnover

The mechanism by which aluminum induces formation of perikaryal neurofilament (NF) inclusions remains unclear. Aluminum treatment inhibits: 1. The incorporation of newly synthesized NF subunits into Triton-insoluble cytoskeleton of axonal neurites; 2. Their degradation and dephosphorylation; 3. Their translocation into axonal neurites. It also fosters the accumulation of phosphorylated NFs within perikarya. In the present study, we addressed the relationship among these effects. Aluminum reduced the assembly of newly synthesized NF subunits into NFs. During examination of those subunits that did assemble in the presence of aluminum, it was revealed that aluminum also interfered with transport of newly assembled NFs into axonal neurites. Similarly, a delay in axonal transport of microinjected biotinylated NF-H was observed in aluminum-treated cells. Aluminum also inhibited the incorporation of newly synthesized and microinjected subunits into the Triton-insoluble cytoskeleton within both perikarya and neurites. Once incorporated into Triton-insoluble cytoskeletons, however, biotinylated subunits were retained within perikarya of aluminum-treated cells to a greater extent than within untreated cells. Notably, these subunits were depleted in the presence and absence of aluminum within 48 h, despite the persistence of the aluminum-induced perikaryal accumulation itself, suggesting that individual NF subunits undergo turnover even within aluminum-induced perikaryal accumulations. These findings demonstrate that aluminum interferes with multiple aspects of neurofilament dynamics and furthermore leaves open the possibility that aluminum-induced perikaryal NF whorls may not represent permanent structures, but rather may require continued recruitment of cytoskeletal constituents.

Aluminum-induced structural alterations of the precursor of the non-A beta component of Alzheimer's disease amyloid

The precursor of the non-A beta component of Alzheimer's disease amyloid (NACP) is a presynaptic protein whose function has been suspected to be tightly involved in neuronal biogenesis including synaptic regulations. NACP was suggested to seed the neuritic plaque formation in the presence of A beta during the development of Alzheimer's disease (AD). Recombinant NACP purified through heat treatment, DEAE-Sephacel anion-exchange, Sephacryl S-200 size-exclusion, and S-Sepharose cation-exchange chromatography steps appeared as a single band on SDS-PAGE with Mr of 19 kDa. Its N-terminal amino acid sequence clearly confirmed that the protein was NACP. Interestingly, however, the protein was split into a doublet on a nondenaturing (ND)-PAGE with equal intensities. The doublet was located slightly above a 45-kDa marker protein on a 12.5% ND-PAGE. In addition, the size of NACP was more carefully estimated as 53 kDa with high-performance gel-permeation chromatography using a TSK G3000sw size-exclusion column. Recently, Lansbury and his colleagues (Biochemistry 35, 13709-13715) have reported that NACP exists as an elongated "natively unfolded" structure which would make the protein more actively involved in protein-protein interactions and Kim (Mol. Cells 7, 78-83) has also shown that the natively unfolded protein is extremely sensitive to proteases. Here, we report that the structure of NACP could be altered by certain environmental factors. Aluminum, a suspected risk factor for AD, converged the doublet of NACP into a singlet with slightly lower mobility on ND-PAGE. Spectroscopic analysis employing uv absorption, intrinsic fluorescence, and circular dichroism indicated that NACP experienced the structural alterations in the presence of aluminum such as the secondary structure transition to generate about 33% alpha-helix. This altered structure of NACP became resistant to proteases such as trypsin, alpha-chymotrypsin, and calpain. Therefore, it is suggested that aluminum, which influences two pathologically critical processes in AD such as the protein turnover and the protein aggregation via the structural modifications, could participate in the disease.

Spinal motor neuron neuroaxonal spheroids in chronic aluminum neurotoxicity contain phosphatase-resistant high molecular weight neurofilament (NFH)

It has previously been shown that a single intracisternal inoculum of AlCl3 in young adult New Zealand white rabbits will induce a dose-dependent phosphatase resistance of high molecular weight neurofilament protein (NFH) that is proportionate to the extent of neurofilamentous inclusion formation (Strong and Jakowec, 1994). To determine if the potential for dissolution of aluminum-induced neurofilamentous inclusions was dependent on the degree of NFH phosphatase resistance, we have examined NFH phosphatase sensitivity in a reversible chronic model of aluminum neurotoxicity. Rabbits receiving repeated intracisternal inoculums of 100 microgram AlCl3 at 28 day intervals until day 267 develop spinal motor neuron perikaryal and neuroaxonal neurofilamentous aggregates in a stereotypic, dose-dependent fashion. In the rabbits receiving inoculums until day 156 with survival until day 267 without further aluminum exposure, neuroaxonal spheroids remained prominent while perikaryal inclusions largely resolved. Immunoreactivity to a monoclonal antibody recognizing phosphorylated NFH (SMI 31) was abolished in perikaryal aggregates at each time interval by dephosphorylation with bovine alkaline phosphatase. However, neuroaxonal spheroids maintained their immunoreactivity. Using time-course dephosphorylation studies of spinal cord homogenates, we observed a significant reduction in the rate of dephosphorylation of NFH following 267 days of AlCl3 exposure (P < 0.05). These observations suggest that neuroaxonal spheroids contain phosphatase-resistant NFH isoforms and that the potential for resolution of intraneuronal neurofilamentous inclusions correlates with the susceptibility of NF within these inclusions to enzymatic dephosphorylation.

Inhibition of proteolysis enhances aluminum-induced perikaryal neurofilament accumulation but does not enhance tau accumulation

As observed for neurons in situ, phosphorylated neurofilament (NF) epitopes are normally segregated within the axonal cytoskeleton of NB2a/d1 cells. However, accumulations of phosphorylated NFs develop in NB2a/d1 perikarya following exposure to aluminum salts and following inhibition of proteolysis. In the present study, we observed that perikarya of cells exposed to both aluminum and the protease inhibitor C1 (also known as "AllNal") were more intensely labeled by monoclonal antibodies directed against both nonphosphorylated and phosphorylated epitopes than were cells treated with either aluminum or protease inhibitor alone. Since these monoclonal antibodies crossreact with tau, we also immunostained cells treated under these conditions with monoclonal antibodies directed against phosphate-insensitive (5E2) and phosphorylated (PHF-1) epitopes of tau. Aluminum treatment, but not C1 treatment, induced accumulation of total tau isoforms as judged by an increase in 5E2 immunoreactivity. Neither treatment, either separately or in combination, induced an increase in PHF-1 immunoreactivity. These findings suggest that alterations in immunoreactivity with SMI antibodies reflected increases in NF epitopes. This was confirmed by immunoblot analyses. Since proteolysis is apparently instrumental in maintaining the normal distribution patterns of phosphorylated NF epitopes, these findings implicate deficiencies in proteolytic mechanisms in the development of neurofibrillary pathology, and underscore the possibility of a multiple etiology in human neuropathological conditions.

Aluminum treatment of intact neuroblastoma cells alters neurofilament subunit phosphorylation, solubility, and proteolysis

Addition of 400 microM AlCl3 to the culture medium for 72 h has been previously shown to induce perikaryal whorls of intermediate-sized filaments in intact mouse NB2a/d1 neuroblastoma cells. Immunoblot analyses demonstrated that in vivo treatment of cells with aluminum induced the de novo appearance of extensively phosphorylated NF-H isoforms in cytoskeletons of undifferentiated cells and increased levels of these isoforms in differentiated cells. Neurofilament subunits isolated from intact cells treated with aluminum were resistant to dephosphorylation in vitro by alkaline phosphatase and to in vitro degradation by endogenous calcium-dependent protease(s). These alterations were accompanied by a greater tendency of neurofilaments to form insoluble aggregates after isolation. These findings demonstrate direct effects of aluminum on neurofilament subunits within intact neuronal cells similar to those previously demonstrated following in vitro exposure of isolated neurofilaments to aluminum.

Effect of neurotoxic metal ions in vitro on proteolytic enzyme activities in human cerebral cortex

In order to develop a clearer understanding of the role of aberrant protein turnover in the pathogenesis of neurodegenerative disorders, the effect of a series of potentially neurotoxic metal ions on a wide range of proteases (lysosomal and cytoplasmic proteinases and peptidases) from human cerebral cortex was determined in vitro. The response of lysosomal and cytoplasmic proteases to inhibition by metal ion species (0.05-5 mmol/l) was broadly similar; Sr2+, Mg2+, Ba2+ or Ca2+ showed little inhibitory effect at any concentration for most protease types, whilst Cu2+, Cd2+, Pb2+, Mg2+ or Zn2+ showed a substantial degree of inhibition, depending on metal ion concentration and enzyme type. Ca2+ activated neutral proteinases were no more susceptible to general metal ion inhibition than most other protease types. Some proteases showed marked activation of activity in the presence of several metal ion species. Both lysosomal and cytoplasmic proteases were relatively insensitive to inhibition by Al3+, compared with that obtained with other metal ion species. It is of note that cathepsin D was particularly resistant to inhibition by most metal ion species, whilst pyroglutamyl aminopeptidase was particularly susceptible to inhibition by low concentrations of many metal ions. The above data suggest that in considering the potential role of neurotoxic metal ions in the pathogenesis of neurodegenerative disorders of the CNS (via protease inhibition in the intracellular protein degradation pathway), attention should be focused on the interactions between a wide range of metal ion species and protease types, rather than be restricted to the Al3+/calpain system (as is presently the case in Alzheimer's disease research). In particular, the potential role of pyroglutamyl aminopeptidase in intracellular protein degradation (in addition to more specialized functions such as neurotransmitter processing) and the pathological consequences of the susceptibility of this enzyme to inhibition by neurotoxic metal ions requires further investigation.

Calcium modulates aluminum neurotoxicity and interaction with neurofilaments

We examined the influence of calcium on neurotoxicity of AlCl3 and Al-lactate toward differentiated NB2a/d1 cells. Apart from induction of perikaryal neurofibrillary inclusions, AlCl3 at 1 mM induced no obvious additional signs of toxicity when added to culture medium in the presence of the normal medium CaCl2 content of 1.8 mM, nor when extracellular calcium was decreased by the addition to the medium of 0.9 mM EDTA. Increasing the extracellular CaCl2 concentration by fivefold was only marginally toxic, but in the presence of AlCl3, reduced viable cell numbers by well over 50% as compared to control cultures, and by approximately 50% vs fivefold CaCl2 alone. A twofold increase in extracellular CaCl2 did not increase the percentage of cells exhibiting Bielschowsky-positive perikarya, but induced a near doubling in the percentage of cells exhibiting accumulations in the presence of 1 mM Al-lactate. AlCl3 (1 mM) retards the electrophoretic migration of NF subunits on SDS-gels. This effect was eliminated by withholding CaCl2 from the incubation mixture and including 5 mM EDTA during incubation of cytoskeletons with AlCl3. The presence of CaCl2 alone did not alter NF migration. These findings underscore the possibility that multiple factors, including those that compromise general neuronal homeostasis, may contribute to neurofibrillary pathology.

Relative susceptibility of cytoskeleton-associated and soluble neurofilament subunits to aluminum exposure in intact cells. A possible mechanism for reduction of neurofilament axonal transport during aluminum neurotoxicity

Previous studies have demonstrated the appearance of phosphorylated neurofilament (NF) subunits within perikaryal cytoskeletons following aluminum exposure. In order to examine the mechanisms leading to this altered distribution of NF subunits, we carried out biochemical analyses of NF subunits in Triton-insoluble and -soluble fractions derived from aluminum-treated NB2a/d1 cells. In addition to increases in the Triton-insoluble cytoskeleton, increases in all three NF subunits were also detected within the Triton-soluble fraction of aluminum-treated cells. To address the nature of this increase in Triton-soluble subunits, aluminum-treated and untreated cultures were harvested in the absence of Triton and fractionated by established procedures to yield fractions greatly enriched for perikarya and neurites, respectively. Each of these subcellular fractions was then subjected to further homogenization in the presence of 1% Triton and centrifugation to yield Triton-insoluble cytoskeletons and Triton-soluble material derived from perikarya and axonal neurites, respectively. Resulting Triton-soluble fractions were "clarified" by high-speed centrifugation to eliminate oligomeric assemblies or soluble neurofilaments. Immunoblot analysis demonstrated quantitative recovery of the aluminum-induced increase in Triton-soluble NF subunits in the perikaryal fraction. Additional aluminum-treated and untreated cultures were pulse-chase radiolabeled with [35S]methionine and fractionated into Triton-insoluble and soluble fractions from isolated perikarya and axonal neurites. Autoradiographic analysis of immunoprecipitated NF subunits revealed that aluminum treatment delayed the translocation of newly synthesized subunits into neurites and resulted in the accumulation of radiolabeled subunits within the Triton-soluble fraction of perikarya. These findings suggest that aluminum may exert a relatively greater effect on NF subunits that have not yet undergone axonal transport and/or incorporation into Triton-insoluble structures vs those that have already deposited into axons. This possibility was supported by the observation that a higher concentration of aluminum was required to alter the electrophoretic migration of in vitro reassembled neurofilaments vs that required for unassembled NF subunits. These findings provide possible mechanisms for the accumulation of NF subunits in perikarya during aluminum intoxication.

Multiple interactions of aluminum with neurofilament subunits: regulation by phosphate-dependent interactions between C-terminal extensions of the high and middle molecular weight subunits

Exposure of individual purified neurofilament (NF) proteins to AlCl3 alters their electrophoretic properties in a time- and concentration-dependent manner, as visualized by their failure to migrate into SDS gels. Co-incubation of purified high (NF-H) and middle (NF-M) but not low (NF-L) molecular weight NF subunits prevents this AlCl3-induced alteration in electrophoretic migration. This latter finding suggested that specific interactions between NF-H and NF-M other than filament formation influenced their interaction with AlCl3. Co-incubation of the 160 kDa alpha-chymotryptic cleavage product of NF-H (corresponding to the highly phosphorylated C-terminal sidearm domain) with native NF-M prevented alteration in subunit electrophoretic migration by AlCl3. By contrast, intact, dephosphorylated NF-H subunits were unable to prevent AlCl3-induced alteration of native NF-M electrophoretic migration. Taken together, these findings suggest that phosphate-dependent interactions between the sidearm extensions of NF-H and NF-M diminish the ability of AlCl3 to associate with either subunit in a manner that alters their electrophoretic migration. This interaction of NF-H and NF-M sidearms is SDS-sensitive, while AlCl3-induced alteration in electrophoretic migration of individual subunits is SDS-resistant. Addition of SDS to mixtures of NF-H and NF-M subunits disrupted the protective effect, and promoted AlCl3-induced alterations in subunit electrophoretic migration. These findings support and extend the current hypothesis that the ability of aluminum to interact with NF subunits is a function of subunit phosphorylation, assembly, and extent of neurofilament-neurofilament cross-linking.

Stable intrachain and interchain complexes of neurofilament peptides: a putative link between Al3+ and Alzheimer disease

The etiologic role of Al3+ in Alzheimer disease has been controversial. Circular dichroism (CD) spectroscopic studies on two synthetic fragments of human neurofilament protein mid-sized subunit (NF-M), NF-M13 (KSPVPKSPVEEKG) and NF-M17 (EEKGKSPVPKSPVEEKG), and their alanine-substituted and/or serine-phosphorylated derivatives were carried out in an attempt to find a molecular mechanism for the effect of Al3+ to induce aggregation of neuronal proteins or their catabolic fragments. Al3+ and Ca2+ ions were found to induce beta-pleated sheet formation in the phosphorylated fragments. The cation sensitivity depended on the length and charge distribution of the sequence and site of phosphorylation. Al3+-induced conformational changes were irreversible to citric acid chelation, whereas Ca(2+)-induced conformational changes were reversible with citric acid. Studies of the alanine derivatives demonstrated which residues affected Al3+ or Ca2+ binding. Peptides containing at least one free (nonphosphorylated) serine residue were shown to form an intramolecular Al3+ complex, rather than an intermolecular one. In the intramolecular (intrachain) complex, the ligand function of the deprotonated serine hydroxyl was delineated [(Al.pepH-1)-type complex]. Ca2+ ions did not show a tendency for intramolecular complexing. The potential role of Al3+ in Alzheimer disease tangle and plaque formation is strongly suggested.

Partial reversal of aluminium-induced neurofibrillary degeneration by desferrioxamine in adult male rabbits

Desferrioxamine, a chelating agent with a high affinity for aluminium, has been reported to slow the clinical progression of dementia associated with Alzheimer's disease [4]. We report here the effects of desferrioxamine treatment on aluminium-induced neurofibrillary degeneration in rabbits. Adult male New Zealand white rabbits received a single injection of aluminium-maltolate into the lateral cerebral ventricle. Three days later, one group of rabbits was treated with intramuscular injections of desferrioxamine twice daily; a second group received saline instead of desferrioxamine. Both groups were sacrificed 4 or 5 days following initiation of desferrioxamine or saline treatment. Minimal neurofibrillary degeneration was found in two of six desferrioxamine-treated rabbits, while all six rabbits treated with saline showed extensive neurofibrillary degeneration, particularly in the ventral horn of the lower spinal cord. Quantitation of the neurofibrillary degeneration in ventral horn neurons of lumbar cord revealed 30% to be affected in saline-treated animals compared to zero-affected neurons following desferrioxamine treatment. When sacrificed just 3 days after aluminium treatment, 50% of the rabbits already revealed neurofibrillary degeneration, corresponding to the time-point when desferrioxamine treatment was begun in the above animals; on quantitation, 7.5% of ventral lumbar cord neurons were involved. These findings indicate a partial reversal of aluminium-induced neurodegeneration by desferrioxamine. Delaying desferrioxamine treatment to 6 days after aluminium administration prevented any reversal of the aluminium effect; all animals had abundant neurofibrillary degeneration as well as a striking basophilic spicular deposit of calcium and argyrophilic material in the leptomeninges, lateral ventricles and brain parenchyma adjacent to these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurofilament deficiency in quail caused by nonsense mutation in neurofilament-L gene

The existence of a neurofilament-deficient mutant of Japanese quail was recently documented (Yamasaki, H., C. Itakura, and M. Mizutani. 1991. Acta Neuropathol. 82:427-434), but the genetic events leading to the neurofilament deficiency have yet to be determined. Our molecular biological analyses revealed that the expression of neurofilament-L (NF-L) gene was specifically repressed in neurons of this mutant. To search for mutation(s) responsible for the shutdown of this gene expression, we cloned and sequenced the NF-L genes in the wild-type and mutant quails. It is eventually found that the NF-L gene in the mutant includes a nonsense mutation at the deduced amino acid residue 114, indicating that the mutant is incapable of producing even a trace amount of polymerization-competent NF-L protein at any situation. The identification of this nonsense mutation provides us with a solid basis on which molecular mechanisms underlying the alteration in the neuronal cytoskeletal architecture in the mutant should be interpreted.