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KIF3A, KIF3B and KIF3C are kinesin-related motor subunits of the KIF3 family that associate to form the kinesin-II motor complex in which KIF3C and KIF3B are alternative partners of KIF3A. We have analysed the expression of Kif3 mRNAs during prenatal murine development. Kif3c transcripts are detectable from embryonic day 12.5 and persist throughout development both in the CNS and in some peripheral ganglia. Comparison of the expression patterns of the Kif3 genes revealed that Kif3c and Kif3a mRNAs colocalize in the CNS, while only Kif3a is also present outside the CNS. In contrast, Kif3b is detectable in several non-neural tissues. We have also performed immunocytochemical analyses of the developing rat brain and have found the presence of the KIF3C protein in selected brain regions and in several fibre systems. Using neuroblastoma cells as an in vitro model for neuronal differentiation, we found that retinoic acid stimulated the expression of the three Kif3 and the kinesin-associated protein genes, although with different time courses. The selective expression of Kif3c in the nervous system during embryonic development and its up-regulation during neuroblastoma differentiation suggest a role for this motor during maturation of neuronal cells.

Kinesins are microtubule-dependent molecular motors involved in intracellular transport and mitosis. Here, we report the cloning, sequencing, mapping, and expression of a novel member of the kinesin superfamily. The sequence of this newly identified human cDNA reveals an open reading frame encoding a putative protein of 792 residues. Based on its high sequence similarity to the kinesin-like molecule KIF3B, we named this protein KIF3C. KIF3C is encoded by transcripts that are distinct from the KIF3B mRNA in human, rat, and mouse and is preferentially expressed in the brain. Fluorescence in situ hybridization reveals that, in the human genome, the KIF3C gene maps to chromosome 2 at 2p23. The sequence of KIF3C predicts an unusually long insertion in the proximity of L11, a region thought to mediate microtubule binding. Taken together, these findings suggest that KIF3C is a novel kinesin-like protein that might be specifically involved in microtubule-based transport in neuronal cells., (Copyright 1998 Academic Press.)

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.

Kinesin is a microtubule-based motor protein involved in organelle transport in neuronal and nonneuronal cells. Although a single kinesin motor has been thought to serve all cell types, we document here that neurons express a second conventional kinesin heavy chain (nKHC) that is 65% identical in amino acid sequence to the ubiquitously expressed kinesin heavy chain (uKHC). By preparing antibodies which distinguish between the two KHCs, we demonstrate that nKHC is a nucleotide-dependent microtubule-binding protein which partially cofractionates with membrane organelles. Immunolocalization experiments show that nKHC is distributed throughout the CNS but is highly enriched in subsets of neurons. In hippocampal neurons in culture, uKHC is distributed uniformly throughout the neuron, whereas nKHC is selectively concentrated in the cell body. These results demonstrate that mammalian neuronal tissue contains two conventional kinesin motors which may serve distinct functions in microtubule-based transport.