Misdirected vimentin messenger RNA alters cell morphology and motility

Localized messenger RNAs were first observed as embryonic determinants that altered development when mislocalized. In recent years localized mRNAs hav e been found for several cytoskeletal proteins, including actin, vimentin a nd several microtubule associated proteins, We sought to determine whether redirecting mRNA for a cytoskeletal protein to an inappropriate address wou ld alter cellular phenotypes. To do so we generated vimentin mRNAs with a m yc epitope tag and the beta-actin 3' untranslated region (3' UTR) as a loca lization signal. When misdirected vimentin mRNAs are expressed in either fi broblasts or SW13 cells, cells develop numerous, extremely long processes; these cells also move more slowly to enter a wound of the monolayer. In sit u hybridization revealed that the misdirected mRNA was often localized in t he processes, in contrast to endogenous vimentin mRNA, The processes usuall y contained actin distal to the transgenic vimentin and microtubules proxim al to it, SW13 cells lacking vimentin produced fewer and shorter processes, suggesting a dominant negative effect that involves recruitment of endogen ous vimentin. Control experiments that transfected in constructs expressing tagged, correctly localized vimentin, or beta-galactosidase that localized through the beta-actin 3' UTR, indicate that neither the shape nor the mot ility changes are solely due to the level of vimentin expression in the cel l, This is direct evidence that the site of expression for at least one cyt oskeletal mRNA alters the phenotype of the cell in which it is expressed, M essenger RNA localization is proving to be as essential for the normal main tenance of somatic cell phenotypes as embryonic determinants are for embryo genesis.