Abstract
Vimentin (Vm) is initially expressed by early neuronal precursors in situ and in culture. Vm is essential for neuritogenesis at least in culture and is gradually replaced by neurofilaments (NFs) because of downโregulation of Vm expression. This period is accompanied by a slowing of axonal elongation. We examined whether continued expression of Vm could foster continued axonal elongation. NB2a/d1 cells differentiated with dibutyryl cAMP were transfected with constructs expressing Vm or the middleโmolecularโweight NF subunit (NFโM) each conjugated to green fluorescent protein (GFP). Axonal neurites of cells expressing GFPโVm were 30% longer than those of nonexpressing cells, or cells expressing GFPโM, and exhibited a decrease in neurite caliber. Expression of GFPโM did not enhance axonal neurite length but significantly increased caliber. These findings provide further evidence of a role for Vm in axonal outgrowth. Culturing of nontransfected cells on laminin increased neurite length, but cells expressing GFPโVm demonstrated an equivalent increase whether cultured on laminin or culture plastic. Axonal neurites of cells expressing GFPโVm turned to avoid a nonfavorable substrate (nitrocellulose), but culturing of these cells on nitrocellulose did not impair axonal outgrowth. These latter findings indicate that the more robust outgrowth following reexpression of Vm is independent of a favorable or nonfavorable substrate but that axonal neurites of these cells still interact with the substrate to the extent that the substrate can influence directionality. ยฉ 2004 WileyโLiss, Inc.