Multiple tubulin forms are expressed by a single neurone

Abstract

Microtubules are a key cytoskeletal constituent of the eukaryotic cell, being involved in mitosis, cell division, cell shape, intracellular transport and motility¹. They are composed of tubulin, a 110,000-molecular weight (M_r) protein which is a dimer of 55,000-M_r α and β submits². Multiple forms of both α-and β- tubulin have been demonstrated biochemically by gel electrophoresis^3,4, column chromatography⁵ and peptide maps⁶; immunologically by monoclonal antibodies⁷; and genetically by mapping multiple tubulin genes in the eukaryotic genome^8–10. There is evidence for multiple tubulin mRNA species^11,12,13, but some of the microheterogeneity may also arise from posttranslational modifications such as phosphorylation¹⁴ and glycosylation¹⁵. Tubulin microheterogeneity is most dramatic in the brain where it could be the result of cellular heterogeneity or a multiplicity of specific functions within each cell, such as neurite extension and axoplasmic transport^1,16. Functional specificity has been demonstrated in particular tubulin subunits in other tissues^9,16,17. To determine whether multiple forms of tubulin coexist in single cells, we have purified and characterized the tubulin of single, isolated sympathetic neurones grown in primary cell culture¹⁸. We show here for the first time that tubulin can be isolated and characterized from a single mammalian neurone. Single neurones exhibit multiple tubulin isoelectric forms, suggesting that structurally different forms of microtubules have functionally different roles in a single cell.