Reexpression of vimentin in differentiated neuroblastoma cells enhances elongation of axonal neurites.

Department of Pharmacology, Vanderbilt University, Nashville, TennesseeVimentin (Vm) is initially expressed by early neuronalprecursors in situ and in culture. Vm is essential forneuritogenesis at least in culture and is gradually re-placed by neurofilaments (NFs) because of down-regulation of Vm expression. This period is accompaniedby a slowing of axonal elongation. We examined whethercontinued expression of Vm could foster continued ax-onal elongation. NB2a/d1 cells differentiated with dibu-tyryl cAMP were transfected with constructs expressingVm or the middle-molecular-weight NF subunit (NF-M)each conjugated to green fluorescent protein (GFP). Ax-onal neurites of cells expressing GFP-Vm were 30%longer than those of nonexpressing cells, or cells ex-pressing GFP-M, and exhibited a decrease in neuritecaliber. Expression of GFP-M did not enhance axonalneurite length but significantly increased caliber. Thesefindings provide further evidence of a role for Vm inaxonal outgrowth. Culturing of nontransfected cells onlaminin increased neurite length, but cells expressingGFP-Vm demonstrated an equivalent increase whethercultured on laminin or culture plastic. Axonal neurites ofcells expressing GFP-Vm turned to avoid a nonfavorablesubstrate (nitrocellulose), but culturing of these cells onnitrocellulose did not impair axonal outgrowth. Theselatter findings indicate that the more robust outgrowthfollowing reexpression of Vm is independent of a favor-able or nonfavorable substrate but that axonal neurites ofthese cells still interact with the substrate to the extentthat the substrate can influence directionality.