The cyanogen bromide peptide maps of neurofilament polypeptides in axonal preparations isolated from bovine brain are different

Microheterogeneity ("neurotypy") of neurofilament proteins

Neurofilaments purified from adult rat brainstem by two methods were electrophoresed on NaDodSO4/polyacrylamide gels to separate the triplet proteins (approximate Mrs of 200,000, 155,000, and 68,000) which, in turn, were electroblotted onto nitrocellulose paper. On Coomassie blue-stained gels that were not electroblotted, the same banding pattern was seen with both methods of preparation. Immunocytochemical staining of the electroblots with each of five monoclonal antibodies revealed that three of the monoclonal antibodies were specific for the Mr 200,000 neurofilament protein and two, for both the Mrs 200,000 and 155,000 neurofilament proteins. None of the antibodies reacted with the Mr 68,000 band. The Mr 200,000 band could be resolved into doublet bands. Individual monoclonal antibodies reacted with either one or both of the Mr 200,000 doublets. The immunocytochemical staining of the neurofilament triplets on electroblots was compared to that of adult rat cerebellar paraffin sections. Each monoclonal antibody had a unique pattern of staining, reacting only with certain subpopulations of neurons or their processes. Correlation of the staining patterns in cerebellar tissue sections with those of neurofilament polypeptides on electroblots suggested that different neurofilament polypeptides can be localized to different structures and subpopulations of neurons and that molecular heterogeneity ("neurotypy") may be revealed within the Mrs 200,000 and 155,000 neurofilament polypeptides.

Preparative separation and amino acid composition of neurofilament triplet proteins

Intact neurofilaments were isolated from bovine spinal cord white matter, washed by sedimentation in 0.1 M-NaCl, and extracted with 8 M-urea. Solubilized neurofilament triplet proteins of molecular weights approximately 68,000 (P68), 150,000 (P150), and 200,000 (P200) were purified by preparative electrophoresis, using an LKB 7900 Uniphor apparatus. The method provides for an enhanced yield of purified protein and has markedly reduced admixture of electrophoresed protein with acrylamide and associated protein contaminants. Amino acid compositions of the purified neurofilament triplet proteins are reported and compared.

Assessment of immunological properties of neurofilament triplet proteins

The relationship between mammalian neurofilament triplet proteins was studied immunologically using rabbit and guinea pig antibodies to bovine neurofilament triplet proteins. Neurofilament proteins were separated by preparative electrophoresis, each protein being isolated and re-electrophoresed to enhance purification. Antisera to 68,000 (P68), 150,000 (P150) and 200,000 (P200) dalton neurofilament proteins showed greatest activity with the corresponding protein immunogen but also revealed cross-reactivity with the other two neurofilament proteins when assessed by the ELISA method. The same antigenic inoculum elicited variable cross-reactivity, more in the guinea pig than in the rabbit. Rabbit antisera to P68 was specific in that it did not cross-react with P150 or P200. Rabbit antisera to P150 and to P200 were rendered specific by absorption with P200 and P150, respectively. By electron microscopy, isolated neurofilaments became decorated with an uniform coat of antibodies when exposed to specific antisera for each of the neurofilament proteins. By indirect immunofluorescence, each antisera showed identical patterns of tissue localization, corresponding to the distribution of neurofilaments in peripheral nerve, spinal ganglia, spinal cord, cerebellum and cerebrum. Neurofilament antigens were not detected in liver, kidney, spleen, lung, bladder, intestine, aorta, heart or tongue.

Similarity of neurofilament proteins from different parts of the rabbit nervous system

In the nervous system, the various populations of neurons perform a large spectrum of functions. Although neurofilaments are a major constituent of the different neurons, the neurofilament protein composition and the expression of the genes specifying these proteins may not be the same throughout the entire nervous system. To investigate these two aspects of the biology of neurofilaments, we have prepared neurofilament-rich fractions from different regions of the nervous system of strains of rabbits known to present a genetically determined polymorphism involving one of the neurofilament polypeptides (P200). Filaments were isolated from brain, spinal cord, sciatic, optic and trigeminal nerves, and lumbar ventral and dorsal roots by a procedure not involving axonal flotation and yielding material suitable for comparative analysis within a single animal. The filaments were compared for their variability as a function of the region from which they were prepared. For any given animal, the neurofilament peptides migrate to identical positions on SDS-gel electropherograms. Whatever allele of P200 is expressed in filaments from one region, the same allele is also expressed in all of the other filament preparations from that animal. On two-dimensional analysis isomorphs of the P68 neurofilament protein are not present in the same amounts in different regions of the nervous system. These results indicate that, although it seems that the gene for the P200 neurofilament protein is expressed uniformly throughout the nervous system, there may be some topographic specificity in the distribution of the other constituent proteins of neurofilaments.

Immunohistochemical localization of the 150K neurofilament protein in the rat and the rabbit

Antisera to the 150K-dalton polypeptide of the bovine neurofilament triplet and chicken neurofilament antisera reacting with the 70K protein in isolated bovine brain filaments stained the same structures in rat cerebellum by immunofluorescence and peroxidase-antiperoxidase methods, that is Purkinje cell baskets, thin nerve fibers in the lower half of the molecular layer and myelinated axons. The 150K bovine neurofilament antisera did not stain large motor neurons in the anterior horns of the spinal cord in rat and rabbit, nor aluminum-induced neurofibrillary tangles in the rabbit. All these structures were demonstrated by the chicken neurofilament antisera and by silver neurofibrillary methods. IDPN-induced axonal balloons containing accumulations of neurofilaments were equally well stained by bovine 150K and chicken neurofilament antisera. These data suggest that the 150K polypeptide of the neurofilament triplet is not a subunit of the neurofilament core and probably plays a role in axonal transport.

Heterogeneity of intermediate filament proteins from rabbit spinal cord

Large amounts of a nerofilament-enriched fraction may be prepared from spinal cord homogenates by a simple, three-step procedure. This involves flotation of filament-containing axon fragments, extraction with Triton X-100, and washing by sedimentation through a sucrose density gradient. The material obtained by this procedure includes both large mats of individual 10-nm filaments and tightly packed bundles of filaments. SDS-gel electrophoresis of these fractions indicates that the fractions are formed of four polypeptides: the three which are generally considered to form neurofilaments (P200, P150, and P68) and another, with a molecular weight of about 50,000 daltons (P50), which is thought to be derived from fibrous astrocytes. Analysis of these filament fractions on two-dimensional gels indicate heterogeneity among each of the different molecular weight classes. The largest polypeptide of neurofilaments, P200, focuses at several spots in the pH gradient. P68 and P150 are more acidic: each appears as a pair of overlapping spots. P50 resolves into a complex of spots of about the same molecular weight but with different isoelectric points. Heterogeneity is not unique to these filament polypeptides but appears to be a characteristic of all fibrous proteins of the nervous system.

Astroglial and axonal proteins in isolated brain filaments. II. Isolation of a 70 000-dalton polypeptide from bovine brain filament preparations by immunoaffinity chromatography with antineurofilament antisera

Antineurofilament antisera raised against chicken brain antigen were used to isolate neurofilament protein from bovine brain filament preparations by immunoaffinity chromatography. Glial fibrillary acidic protein, the subunit of glial filaments, passed unabsorbed through the column. The Mr 70 000 component of the neurofilament triplet was tightly absorbed to the column and essentially the only protein eluted at pH 2.5. The other two components of the triplet, of approximately 200 000 and 150 000 daltons, were less tightly attached to the column and eluted at pH 6.0 in 5 M urea.

Immunohistochemical characterization of neurofibrillary tangles induced by mitotic spindle inhibitors

Neurofibrillary tangles were induced in the motor neurons of the rabbit spinal cord by the intrathecal injection of colchicine, vinblastine, and vincristine. The tangles stained intensely by immunofluorescence and by the peroxidase-anti-peroxidase procedure using neurofilament antisera raised against chicken brain antigen, as previously reported for aluminum-induced neurofibrillary tangles. No immunohistochemical reactivity could be demonstrated between the tangles and a 150,000 dalton bovine neurofilament antiserum, although the adjacent axons were intensely stained in cryostat sections of the spinal cord.