Expression of neuronal kinesin heavy chain is developmentally regulated in the central nervous system of the rat

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 approximately 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.