Immunoelectronmicroscopical localization of the three neurofilament triplet proteins along neurofilaments of cultured dorsal root ganglion neurones

Correlated immunofluorescence and electron microscopy was used to study neurofilament expression, organization and structure in cultured neurones of newborn rat dorsal root ganglia. The results extend previous immunofluorescent data subdividing the neurones into two main classes: neurones rich in neurofilaments, expressing all three triplet proteins and neurones without noticeable neurofilaments which cannot be stained positively for any of the triplet proteins. The two classes are identified as the large light cells and small dark cells characteristically found in adult dorsal root ganglia in situ. Further ultrastructural characterization identifies the various subclasses of each major class in the cultures used. Cytoskeletons of neurofilament-rich neurones decorated by antibodies specific for each triplet protein lead to the following model. All three triplet proteins are associated with each individual filament, although the antibodies show a different localization. Whereas the 68K protein seems to form the backbone of the filament, the 200K protein is periodically arranged (repeat approx. 100 nm) in a more peripheral position. The 145 K protein is revealed in a nearly continuous manner along the filament.