The organization of 10 nm filaments and microtubules in embryonic neurons from spinal ganglia.

The distribution of tubulin and 10 nm filament protein: vimentin and the 70 K neurofilament component, was investigated in cultures of dorsal root ganglion cells by indirect immunofluorescence using antisera specific for these proteins. The neuronal cell bodies and the neurites in these cultures were brightly stained. Fibres stained with both tubulin and 10 nm filament antibodies were visible at branch points, whereas only microtubules extended into growth cones, including those that were in the process of bifurcation. Differences in the arrangement of microtubules and 10 nm filaments were also detected during colcemid-induced neurite retraction. After complete retraction, perinuclear coils of 10 nm filaments were found in the cell bodies whereas only very weak diffuse tubulin staining was visible. When regrowth commenced on removal of colcemid, microtubule organizing centres were visible in the cell bodies and were then rapidly obscured by bright staining which later extended into the neurite stump. Similarly, the 10 nm coils were replaced by fibrous staining which also projected into the growing neurite. These observations suggest that the extension of microtubules and 10 nm filaments is both co-ordinated and sequential, with microtubules having a dynamic role in growth and 10 nm filaments stabilizing the pattern of growth thereafter.