Giant axonal neuropathy: an inborn error of organization of intermediate filaments

Intermediate filament aggregates cause mitochondrial dysmotility and increase energy demands in giant axonal neuropathy

Intermediate filaments (IFs) are cytoskeletal polymers that extend from the nucleus to the cell membrane, giving cells their shape and form. Abnormal accumulation of IFs is involved in the pathogenesis of number neurodegenerative diseases, but none as clearly as giant axonal neuropathy (GAN), a ravaging disease caused by mutations in GAN, encoding gigaxonin. Patients display early and severe degeneration of the peripheral nervous system along with IF accumulation, but it has been difficult to link GAN mutations to any particular dysfunction, in part because GAN null mice have a very mild phenotype. We therefore established a robust dorsal root ganglion neuronal model that mirrors key cellular events underlying GAN. We demonstrate that gigaxonin is crucial for ubiquitin-proteasomal degradation of neuronal IF. Moreover, IF accumulation impairs mitochondrial motility and is associated with metabolic and oxidative stress. These results have implications for other neurological disorders whose pathology includes IF accumulation.

Kelch Domain of Gigaxonin Interacts with Intermediate Filament Proteins Affected in Giant Axonal Neuropathy

Patients with giant axonal neuropathy (GAN) show progressive loss of motor and sensory function starting in childhood and typically live for less than 30 years. GAN is caused by autosomal recessive mutations leading to low levels of gigaxonin (GIG), a ubiquitously-expressed BTB/Kelch cytoplasmic protein believed to be an E3 ligase substrate adaptor. GAN pathology is characterized by aggregates of intermediate filaments (IFs) in multiple tissues. To delineate the molecular pathway between GIG deficiency and IF pathology, we undertook a proteomic screen to identify the normal binding partners of GIG. Prominent among them were several classes of IFs, including the neurofilament subunits whose accumulation leads to the axonal swellings for which GAN is named. We showed these interactions were dependent on the Kelch domain of GIG. Furthermore, we identified the E3 ligase MYCBP2 and the heat shock proteins HSP90AA1/AB1 as interactors with the BTB domain that may result in the ubiquitination and subsequent degradation of intermediate filaments. Our open-ended proteomic screen provides support to GIG’s role as an adaptor protein, linking IF proteins through its Kelch domain to the ubiquitin pathway proteins via its BTB domain, and points to future approaches for reversing the phenotype in human patients.

Intermediate filament protein accumulation in motor neurons derived from giant axonal neuropathy iPSCs rescued by restoration of gigaxonin

Giant axonal neuropathy (GAN) is a progressive neurodegenerative disease caused by autosomal recessive mutations in the GAN gene resulting in a loss of a ubiquitously expressed protein, gigaxonin. Gene replacement therapy is a promising strategy for treatment of the disease; however, the effectiveness and safety of gigaxonin reintroduction have not been tested in human GAN nerve cells. Here we report the derivation of induced pluripotent stem cells (iPSCs) from three GAN patients with different GAN mutations. Motor neurons differentiated from GAN iPSCs exhibit accumulation of neurofilament (NF-L) and peripherin (PRPH) protein and formation of PRPH aggregates, the key pathological phenotypes observed in patients. Introduction of gigaxonin either using a lentiviral vector or as a stable transgene resulted in normalization of NEFL and PRPH levels in GAN neurons and disappearance of PRPH aggregates. Importantly, overexpression of gigaxonin had no adverse effect on survival of GAN neurons, supporting the feasibility of gene replacement therapy. Our findings demonstrate that GAN iPSCs provide a novel model for studying human GAN neuropathologies and for the development and testing of new therapies in relevant cell types.

New mutations, genotype phenotype studies and manifesting carriers in giant axonal neuropathy

Giant axonal neuropathy (GAN; MIM 256850) is a severe childhood onset autosomal recessive sensorimotor neuropathy affecting both the peripheral nerves and the central nervous system. Bomont and colleagues identified a novel ubiquitously expressed gene they named Gigaxonin on chromosome 16q24 as the cause of GAN in a number of families. We analysed five families with GAN for mutations in the Gigaxonin gene and mutations were found in four families; three families had homozygous mutations, one had two compound heterozygous mutations and one family had no mutation identified. All families had the typical clinical features, kinky hair and nerve biopsy. We report some unusual clinical features associated with GAN and Gigaxonin mutations as well as confirm the heterogeneity in GAN and the identification of two families with manifesting carriers.

The dynamic and motile properties of intermediate filaments

For many years, cytoplasmic intermediate filaments (IFs) were considered to be stable cytoskeletal elements contributing primarily to the maintenance of the structural and mechanical integrity of cells. However, recent studies of living cells have revealed that IFs and their precursors possess a remarkably wide array of dynamic and motile properties. These properties are in large part due to interactions with molecular motors such as conventional kinesin, cytoplasmic dynein, and myosin. The association between IFs and motors appears to account for much of the well-documented molecular cross talk between IFs and the other major cytoskeletal elements, microtubules, and actin-containing microfilaments. Furthermore, the associations with molecular motors are also responsible for the high-speed, targeted delivery of nonfilamentous IF protein cargo to specific regions of the cytoplasm where they polymerize into IFs. This review considers the functional implications of the motile properties of IFs and discusses the potential relationships between malfunctions in these motile activities and human diseases.

Cerebral proton magnetic resonance spectroscopy of a patient with giant axonal neuropathy

Magnetic resonance imaging of a girl with giant axonal neuropathy revealed a progressive white matter disease. In close agreement with histopathological features reported previously, localized proton magnetic resonance spectroscopy at 9 and 12 years of age indicated a specific damage or loss of axons (reduced N-acetylaspartate and N-acetylaspartylglutamate) accompanied by acute demyelination (elevated choline-containing compounds, myo-inositol, and lactate) in white matter as well as a generalized proliferation of glial cells (elevated choline-containing compounds and myo-inositol) in both gray and white matter.

A requirement for cytoplasmic dynein and dynactin in intermediate filament network assembly and organization

We present evidence that vimentin intermediate filament (IF) motility in vivo is associated with cytoplasmic dynein. Immunofluorescence reveals that subunits of dynein and dynactin are associated with all structural forms of vimentin in baby hamster kidney-21 cells. This relationship is also supported by the presence of numerous components of dynein and dynactin in IF-enriched cytoskeletal preparations. Overexpression of dynamitin biases IF motility toward the cell surface, leading to a perinuclear clearance of IFs and their redistribution to the cell surface. IF-enriched cytoskeletal preparations from dynamitin-overexpressing cells contain decreased amounts of dynein, actin-related protein-1, and p150Glued relative to controls. In contrast, the amount of dynamitin is unaltered in these preparations, indicating that it is involved in linking vimentin cargo to dynactin. The results demonstrate that dynein and dynactin are required for the normal organization of vimentin IF networks in vivo. These results together with those of previous studies also suggest that a balance among the microtubule (MT) minus and plus end-directed motors, cytoplasmic dynein, and kinesin are required for the assembly and maintenance of type III IF networks in interphase cells. Furthermore, these motors are to a large extent responsible for the long recognized relationships between vimentin IFs and MTs.

The gene encoding gigaxonin, a new member of the cytoskeletal BTB/kelch repeat family, is mutated in giant axonal neuropathy

Disorganization of the neurofilament network is a prominent feature of several neurodegenerative disorders including amyotrophic lateral sclerosis (ALS), infantile spinal muscular atrophy and axonal Charcot-Marie-Tooth disease. Giant axonal neuropathy (GAN, MIM 256850), a severe, autosomal recessive sensorimotor neuropathy affecting both the peripheral nerves and the central nervous system, is characterized by neurofilament accumulation, leading to segmental distension of the axons. GAN corresponds to a generalized disorganization of the cytoskeletal intermediate filaments (IFs), to which neurofilaments belong, as abnormal aggregation of multiple tissue-specific IFs has been reported: vimentin in endothelial cells, Schwann cells and cultured skin fibroblasts, and glial fibrillary acidic protein (GFAP) in astrocytes. Keratin IFs also seem to be alterated, as most patients present characteristic curly or kinky hairs. We report here identification of the gene GAN, which encodes a novel, ubiquitously expressed protein we have named gigaxonin. We found one frameshift, four nonsense and nine missense mutations in GAN of GAN patients. Gigaxonin is composed of an amino-terminal BTB (for Broad-Complex, Tramtrack and Bric a brac) domain followed by a six kelch repeats, which are predicted to adopt a beta-propeller shape. Distantly related proteins sharing a similar domain organization have various functions associated with the cytoskeleton, predicting that gigaxonin is a novel and distinct cytoskeletal protein that may represent a general pathological target for other neurodegenerative disorders with alterations in the neurofilament network.

A case of giant axonal neuropathy showing focal aggregation and hypophosphorylation of intermediate filaments

We report here the clinicopathological features of a typical case of giant axonal neuropathy (GAN). Scanning electron microscopy of the hair of this case revealed an extraordinarily irregular cuticle. Focal accumulation of intermediate filaments in axons, Schwann cells, muscle fibers and skin fibroblasts were also found under an electron microscopy. When examined immunocytochemically, muscle fibers exhibited local disruption of the filamentous network in the subsarcolemmal space and in the central cytoplasm accompanied by focal accumulation of desmin. The intracellular network of vimentin was also disrupted, exhibiting global accumulation in some of the cultured skin fibroblasts. Decreased interneurofilament spacing was found in enlarged axons, suggesting the presence of hypophosphorylation of neurofilaments in this patient. These findings suggest general disorganization, abnormal distribution and possible defective phosphorylation of intermediate filaments in GAN.

Localization of the giant axonal neuropathy gene to chromosome 16q24

Giant axonal neuropathy (GAN) is a degenerative disorder of the peripheral nerves that is inherited as an autosomal recessive trait, presenting in early childhood and progressing to death, usually by late adolescence. Diagnosis is made by peripheral nerve biopsy, in which a striking pathological finding is seen--fibers distorted by giant axonal swellings filled with densely packed bundles of neurofilaments (the primary intermediate filament in neurons), with segregation of other axoplasmic organelles. In addition to disorganized neurofilaments in nerve, disorganization of other members of the intermediate filament family of proteins is seen in other tissues; this implies that the underlying defect is one of generalized intermediate filament organization, with neurofilaments predominantly affected. We have pursued a genomewide search for regions of homozygosity of descent in 5 consanguineous families. A 5.3-cM region of homozygosity, shared in all 5 families, was found on chromosome 16q24, and linkage was established to this locus with a LOD score of 4.18 at theta = 0.00 at the most tightly linked marker, D16S3098. Determination of this locus is the first step toward characterizing the gene responsible for a fundamental property of intermediate filament organization and may shed light on other disorders (such as amyotrophic lateral sclerosis) in which neurofilament pathology is prominent.

Aggregation of a subpopulation of vimentin filaments in cultured human skin fibroblasts derived from patients with giant axonal neuropathy

Giant axonal neuropathy (GAN) is a generalized disorder of intermediate filament networks which results in the formation of an ovoid aggregate in a large variety of cell types. We investigated the cytoskeletal organization of cultured skin fibroblasts derived from three GAN patients by indirect immunofluorescence, confocal, and electron microscopy. Whereas the organization of microfilaments seemed normal, the microtubule network appeared disorganized and tangled. The organization of the intermediate filament network, composed of vimentin, was probed with three antibodies directed against different epitopes: two vimentin-specific antibodies, a monoclonal antibody (mAb V9) and a polyclonal antibody, and a serum specific for all type III IFPs (PI serum). These experiments showed that 20% of cultured skin fibroblasts from GAN patients have a vimentin aggregate composed of densely packed filaments which coexists with a well-organized vimentin network. After depolymerization of microtubules with nocodazole, all fibroblasts from GAN patients contained a vimentin aggregate which seemed to arise from a subpopulation of vimentin filaments normally integrated in the vimentin network. Such aggregates were never observed in any condition in control fibroblasts. Moreover, the ultrastructural analysis of GAN cells revealed the presence of swollen mitochondria. We suggest that GAN may be due to a defect in a factor which stabilizes cytoplasmic intermediate filament networks, and we speculate on its identification and properties.

Axonal neurofilamentous accumulations: a comparison between human and canine giant axonal neuropathy and 2,5-HD neuropathy

The neuropathy produced by the hexacarbon 2,5-hexanedione (2,5-HD) resembles human and canine inherited giant axonal neuropathy (GAN) in the presence of giant axonal swellings that contain accumulations of neurofilaments. The accumulations are both paranodal and internodal in GAN and 2,5-HD induced neuropathy. Detailed morphometry on the neurofilaments reveals that the changes in human and canine GAN are closely similar and differ from those of 2,5-HD neuropathy, suggesting that the mechanisms underlying the formation of the axonal neurofilamentous accumulations differ between the two conditions. In both human and canine GAN, the neurofilaments are more closely spaced and are of greater diameter than in 2,5-HD neuropathy. The changes in the NF in GAN may be the consequence of flattening of the side-arms of the neurofilaments against the axis of the filaments.

Cytoskeletal changes induced by 2,5-hexanedione on developing human neurons in vitro

Dissociated dorsal root ganglion cells from human fetuses were exposed to 2,5-hexanedione (2,5-HD) for 2 weeks. Morphological changes induced by 2,5-HD consisted in focal neurofilament (NF)-containing enlargements preferentially located in distal, preterminal regions of unmyelinated fibers. Tangles of NF were also observed in the perikarya of nerve cells. Morphometric analysis disclosed that the cross-sectional areas of the 2,5-HD treated axons were 30% smaller than those of control axons. This alteration was associated with reduction of number of NF per unit area. These findings demonstrate that 2,5-HD treatment induces a generalized disorganization of neuronal and axonal NF responsible for focal enlargements as well as atrophic changes of unmyelinated fibers.

Anaesthesia for a patient with giant axonal neuropathy

Giant axonal neuropathy is a generalised disorder of cytoplasmic intermediate filaments which particularly involves the peripheral and central nervous systems. In this paper we describe a child with giant axonal neuropathy and discuss the anaesthetic management in the light of the pathology and physiology of the condition.

Giant axonal neuropathy: clinical, electrophysiologic, and neuropathologic features in two siblings

Giant axonal neuropathy is a progressive central-peripheral axonopathy characterized by distention of axons by aggregated neurofilaments. We report two female siblings with giant axonal neuropathy. Both patients developed symptoms of a chronic progressive polyneuropathy at age 3 years. Clinical evidence of central nervous system involvement was present in both cases. Autopsy neuropathologic examination of the older sibling at the age of 11 years revealed numerous giant axons, Rosenthal fibers, and gliosis throughout the brain and spinal cord and typical giant axons in the peripheral nerves. Electrophysiologic studies in the younger sibling indicated brain stem dysfunction, and her sural nerve biopsy revealed enlarged axons packed with neurofilaments. These patients illustrate that neurologic deficits of giant axonal neuropathy result from widespread lesions in the central, as well as peripheral (including autonomic), nervous systems. This occurrence of giant axonal neuropathy in two siblings supports a genetic origin of this disease. This is the first report of autopsy findings in giant axonal neuropathy in an affected sibling.

Giant axonal neuropathy: studies with sulfhydryl donor compounds

Giant axonal neuropathy (GAN) is a disorder characterized pathologically by distal neurofilament-filled bulbous swellings in axons, and widespread collection of intermediate filaments, including masses of vimentin filaments in cultured skin fibroblasts. A morphologically similar neurofibrillary disorder is produced by acrylamide and the toxic hexacarbons, agents which bind to thiol groups. We report, in GAN fibroblasts, inhibition of vimentin filament aggregation by dithiothreitol and penicillamine, sulfhydryl donor compounds which stabilize thiols. In addition, we describe clinical improvement in a GAN patient treated with penicillamine, despite earlier progressive disease. These findings support the hypothesis of disordered thiol metabolism in GAN, and open up avenues for further research.

Giant axonal neuropathy. A review

First reported in 1972 by Berg & colleagues, giant axonal neuropathy is a generalized disorder of cytoplasmic intermediate filaments affecting the nervous system particularly. The condition was originally thought to be a disorder of the peripheral nervous system, but clinical and pathological evidence has now accumulated which indicates that the brain and spinal cord are progressively involved. Over 20 cases have been reported to date. All cases reported have developed clumsiness and progressive weakness with hyporeflexia in the first seven years of life. Later dysarthria, cerebellar signs and pyramidal tract disturbances appear. Mental retardation, dementia and seizures are sometimes seen. Tightly curled hair is characteristic of, but not invariably present in, the condition. This disorder, as well as a similar condition affecting dogs, appears to be transmitted by autosomal recessive inheritance. No treatment is effective. Most cases are wheelchair bound or dead by the end of the second decade.

Axonal transport in neurological disease

The axonal transport systems have a wide variety of primary roles and secondary responses in neurological disease processes. Recent advances in understanding these roles have built on the increasingly detailed insights into the cell biology of the axon and its supporting cells. Fast transport is a microtubule-based system of bidirectional movement of membranous organelles; the mechanism of translocation of these organelles involves novel proteins, including the recently described protein of fast anterograde transport, kinesin. Slow transport conveys the major cytoskeletal elements, microtubules, and neurofilaments. Several types of structural changes in diseased nerve fibers are understood in terms of underlying transport abnormalities. Altered slow transport of neurofilaments produces changes in axonal caliber (swelling or atrophy) and is involved in some types of perikaryal neurofibrillary abnormality. Secondary changes in slow axonal transport--for example, the reordered synthesis and delivery of cytoskeletal proteins after axotomy--also can produce changes in axonal caliber. Secondary demyelination can be a prominent late consequence of a sustained alteration of neurofilament transport. Impaired fast transport is found in experimental models of distal axonal degeneration (dying back). Retrograde axonal transport provides access to the central nervous system for agents such as polio virus and tetanus toxin, as well as access for known and hypothetical trophic factors. Correlative studies of axonal transport, axonal morphometry, cytoskeletal ultrastructure, and molecular biology of cytoskeletal proteins are providing extremely detailed reconstructions of the pathogenesis of experimental models of neurological disorders. A major challenge lies in the extension of these approaches to clinical studies.

Childhood giant axonal neuropathy. Case report and review of the literature

Giant axonal neuropathy (GAN) is a rare autosomal recessive childhood disorder characterized by a peripheral neuropathy and features of central nervous system involvement. Typically seen are distal axonal swellings filled with 8-10 nm in diameter neurofilaments in central and peripheral axons, and intermediate filament collections in several other cell types. Many neurotoxins produce a morphologically similar neuropathy in humans and experimental animals. Defective nerve fiber energy metabolism has been postulated as a cause in these toxic neuropathies. It is possible that GAN represents an inborn error of metabolism of enzyme-linked sulfhydryl containing proteins, resulting in impaired production of energy necessary for the normal organization of intermediate filaments.

Characterization of the intermediate filament apparatus in skin fibroblasts from patients with giant axonal neuropathy: effect of trypsin

Skin fibroblasts from two siblings with giant axonal neuropathy (GAN) were examined by both biochemical and immunocytochemical studies. The presence of intermediate filaments (IF) characteristic of these cells was affected by the growth conditions. Immediately after plating and during the following 24 hours the majority of the cells contained an IF "bundle"; however, after 4-6 days in culture only a minority of the cells retained this structure. We present evidence that trypsinization but not serum concentration is likely to influence the formation of the "bundle." The results indicate that the formation of the "bundle" may result from a defective association or relationship between the cytoskeleton and the plasma membrane.

Giant axonal neuropathy. A neuropathological study

Giant axonal neuropathy (GAN) is a disease characterized by a slowly progressive neuropathy and signs of central involvement, manifested by visual impairment, corticospinal tract dysfunction, ataxia, and dementia. Pathological hallmarks of the disease include axonal swellings packed with neurofilaments in both peripheral and central nervous systems, and accumulations of intermediate filaments in Schwann cells, fibroblasts, melanocytes, endothelial, and Langerhans cells. Rosenthal fibers, sometimes appearing in masses and mimicking Alexander's disease, emerge as a conspicuous characteristic in longstanding GAN.

Immunoextraction of lipoamide dehydrogenase from cultured skin fibroblasts in patients with combined alpha-ketoacid dehydrogenase deficiency

Combined deficiency of the pyruvate, alpha-ketoglutarate and branched-chain keto acid dehydrogenase complexes is a rare condition in which activity of lipoamide dehydrogenase is either reduced or grossly deficient. Activities in three cell strains from patients with excretion of branched chain ketoacids and alpha-ketoglutarate and lactic-acidemia showed decreased levels of the three alpha-ketoacid dehydrogenases. Lipoamide dehydrogenase activity was 5% of normal in one cell stain and 50-60% in the other two. Antiserum raised against lipoamide dehydrogenase was used to immunoprecipitate labelled lipoamide dehydrogenase from fibroblasts grown on [35S]methionine. After separation of cell proteins from control fibroblasts by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and fluorography, a prominent 55 kilodalton band was evident in cell extracts treated with the antiserum which corresponded to lipoamide dehydrogenase. In the cell lines from patients with combined alpha-ketoacid dehydrogenase deficiency immunoprecipitation of lipoamide dehydrogenase showed that this protein was present in similar amounts to that seen in control cell lines and was also of the correct molecular weight.

Molecular mechanisms of diketone neurotoxicity

The important industrial and commercial solvents n-hexane and methyl n-butyl ketone undergo metabolic conversion in experimental animals and man to the neurotoxic gamma-diketone 2,5-hexanedione. Several molecular mechanisms of action have been proposed to explain the pathogenesis of gamma-diketone neuropathy. Such a mechanism must account for the target organ specificity, neurofilament accumulation, structure/activity relationships, in vivo covalent binding, and apparent direct axonal toxicity encountered in this syndrome. It has been proposed that the gamma-diketones exert their effects by reaction with sulfhydryl moieties of energy-producing axonal glycolytic enzymes, with resultant disruption of axoplasmic transport. Others have suggested that reaction instead occurs with lysine moieties of axonal cytoskeletal proteins to form alkyl pyrrole adducts, leading to damaging physicochemical changes in these proteins. Additional hypotheses involve inhibition of axonal sterologenesis, alterations in nerve membrane properties, and reduced neurofilament proteolysis within the nerve terminal. Although a comprehensive mechanism of action for the gamma-diketones remains to be demonstrated, much progress has been made toward this goal. Ultimate success awaits elucidation of the interactions of the neurotoxic diketones with axonal components at the molecular level. Previous reviews have addressed the historical, pharmacokinetic, and neuropathological aspects of this neuropathy. The present critique will examine proposed molecular mechanisms for the gamma-diketones with regard to theoretical considerations and experimental evidence.

Giant axonal neuropathy: a conditional mutation affecting cytoskeletal organization

Giant axonal neuropathy (GAN) results from autosomal recessive mutations (gan-) that affect cytoskeletal organization; specifically, intermediate filaments (IFs) are found collapsed into massive bundles in a variety of different cell types. We studied the gan- fibroblast lines WG321 and WG139 derived from different GAN patients. Although previous studies implied that the gan- IF phenotype was constitutive, we find that it is conditional. That is, when cells were grown under the permissive condition of medium containing over 2% fetal calf serum, most cells had normal IF organization. IF bundles formed when gan- cells were transferred to the nonpermissive condition of low (0.1%) serum. Microtubule organization appeared normal in the presence or absence of serum. The effect of serum starvation was largely blocked or reversed by the addition of BSA to the culture media. We found no evidence that the gan- phenotype depends upon progress through the cell cycle. We discuss the possible role of serum effects in the etiology of GAN and speculate as to the molecular nature of the gan- defect.

Role of cytoskeletal elements in the retractile activity of human skin fibroblasts

Giant axonal neuropathy skin fibroblasts, which are characterized by a selective and partial disorganization of vimentin filaments [1] exhibited, when compared with normal skin fibroblasts, less fibrin clot retractile (FCR) activity and spreading within the fibrin clot both during active growth and resting stage. Skin fibroblasts derived from patients affected with adenomatosis of the colon and rectum, which display a disorganized actin network [2], exhibited reduced FCR activity and spreading within the fibrin clot only during resting stage. FCR inhibition was also obtained by treating the cells with colcemid, cytochalasin B (CB) and dihydrocytochalasin B. The data suggest that FCR activity is under the control of different cytoskeletal structures. For the first time, a direct involvement of intermediate-sized filaments could be demonstrated in the interaction between fibroblasts and an organic substratum.

The neurotoxins 2,5-hexanedione and acrylamide promote aggregation of intermediate filaments in cultured fibroblasts

Axonal swellings associated with large aggregates of neurofilaments are characteristic of neuropathies caused by chemical neurotoxins (n-hexane, methyl n-butyl ketone, and acrylamide) or giant axonal neuropathy (GAN--an autosomal recessive genetic disease). In GAN, filamentous aggregates have been shown also to occur in other cell types including cultured skin fibroblasts. Therefore, we studied the effects of 2,5-hexanedione (the neurotoxic metabolite of n-hexane and methyl n-butyl ketone) and acrylamide on normal human skin fibroblasts in tissue culture. We show that both neurotoxins induce aggregation of intermediate filaments of the vimentin type in the cultured fibroblasts without disrupting microtubules.

The surface glycoproteins of human skin fibroblasts detected after electrophoresis by the binding of peanut (Arachis hypogaea) agglutinin and Ricinus communis (castor-bean) agglutinin I

A new methodology was developed to study the cell-surface glycoproteins of cultured human skin fibroblasts. This was based on the binding of a variety of biotinyl-lectins to nitrocellulose electrophoretic transfers of total fibroblast lysates after separation in sodium dodecyl sulphate/polyacrylamide gels, followed by reaction with avidin-biotinyl-peroxidase complexes and detection with 3,3'-diaminobenzidine. The technique proved to be very sensitive and a large number of glycoproteins were detected by binding of concanavalin A and wheat-germ agglutinin. Binding of peanut agglutinin and to a lesser extent of Ricinus communis agglutinin I were found to be dependent on prior removal of sialic acid residues from the glycoproteins. Since by treatment of intact viable cells with neuraminidase only external sialic acid residues were removed, peanut agglutinin and Ricinus communis agglutinin I could thus be utilized for selective detection of cell-surface glycoproteins. Also, because peanut agglutinin was known to bind preferentially to oligosaccharides of the O-glycosidic type, and Ricinus communis agglutinin I to those of the N-glycosidic type, the two lectins were complementary in displaying the surface glycoproteins and in providing information about their oligosaccharide composition.