Kinesin is a microtubule-based motor protein involved in intracellular organelle transport. Neurons are characterized by the presence of at least two isoforms of conventional kinesin: ubiquitous kinesin, expressed in all cells and tissues, and neuronal kinesin, whose pattern of expression is confined to neuronal cells. In order to investigate whether the two kinesin motors, which are encoded by different genes, may play distinct biological roles in neurons, we studied their expression during neuronal differentiation. Human neuroblastoma SH-SY5Y and IMR32 cells and rat phaeochromocytoma PC12 cells were used as an in vitro system for neuronal differentiation and were induced to differentiate in the presence of retinoic acid, a combination of dibutyryl cAMP and 5-bromodeoxyuridine, and nerve growth factor respectively. The expression level of each kinesin isoform was evaluated by quantitative immunoblot before and after pharmacological treatment. We found that in all cell types the expression level of neuronal kinesin, but not of ubiquitous kinesin, is stimulated during differentiation. In particular, SH-SY5Y cells show a 4.5-fold, IMR32 cells a 3-fold and PC12 cells a 7-fold increase in the level of expression of neuronal kinesin. By Northern blot analysis we found that the selective increase in the expression of neuronal kinesin is paralleled by an increase in its mRNA, indicating that there is a transcriptional control of the expression of this kinesin isoform during differentiation of neuroblastoma and PC12 cells. Our results suggest that these cells represent an adequate model to study the function of conventional kinesin and its isoforms.

Abstract:The kinesin family of motor proteins comprises at least two isoforms of conventional kinesin encoded by different genes: ubiquitous kinesin, expressed in all cells and tissues, and neuronal kinesin, expressed exclusively in neuronal cells. In the present study, we have analyzed the expression of the two kinesin isoforms by immunochemistry at different stages of development of the rat CNS. We have found that the level of expression of neuronal kinesin is five to eight times higher in developing than in adult rat brains, whereas that of ubiquitous kinesin is only~2.5 times higher in maturing versus adult brains. Moreover, we have studied the distribution of neuronal kinesin by light microscopic immunocytochemistry in the rat brain at different postnatal ages and have found this protein not only to be more highly expressed in juvenile than in adult rat brains but also to show a different pattern of distribution. In particular, tracts of axonal fibers were clearly stained at early postnatal stages of development but were markedly unlabeled in adult rat brains. Our results indicate that the expression of at least one isoform of conventional neuron-specific kinesin is up-regulated in the developing rat CNS and suggest that this protein might play an important role in microtubule-based transport during the maturation of neuronal cells in vivo. Key Words: Microtubule-based motors-Conventional kinesin isoforms-Quantitative protein expression-Immunocytochemical localization-Brain development.