EXPRESSION OF THE MITOTIC MOTOR PROTEIN CHO1 MKLPI IN POSTMITOTIC NEURONS/

The kinesin-related motor protein CHO1/MKLP1 was initially thought to be expressed only in mitotic cells, where it presumably transports opp ositely oriented microtubules relative to one another in the spindle m id-zone. We have recently shown that CHO1/MKLP1 is also expressed in c ultured neuronal cells, where it is enriched in developing dendrites [ Sharp et al. (1997a) J. Cell Biol., 138, 833-843]. The putative functi on of CHO1/MKLP1 in these postmitotic cells is to intercalate minus-en d-distal microtubules among oppositely oriented microtubules within de veloping dendrites, thereby establishing their non-uniform microtubule polarity pattern, Here we used in situ hybridization to determine whe ther CHO1/MKLP1 is expressed in a variety of rodent neurons both in vi vo and in vitro. These analyses revealed that CHO1/MKLP1 is expressed within various neuronal populations of the brain including those in th e cerebral cortex, hippocampus, olfactory bulb and cerebellum. The mes senger ribonucleic acid (mRNA) levels are high within these neurons we ll after the completion of their terminal mitotic division and through out the development of their dendrites. After this, the levels decreas e and are relatively low within the adult brain. Parallel analyses on developing hippocampal neurons in culture indicate that the levels of expression increase dramatically just prior to dendritic development, and then decrease somewhat after the dendrites have differentiated. Do rsal root ganglion neurons, which generate axons but not dendrites, ex press significantly lower levels of mRNA for CHO1/MKLP1 than hippocamp al or sympathetic neurons, These results are consistent with the propo sed role of CHOI/MKLP1 in establishing the dendritic microtubule array .