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.