The nuclear/mitotic apparatus protein NuMA is a component of the somatodendritic microtubule arrays of the neuron

Neurons are terminally post-mitotic cells that utilize their microrubule ar rays for the growth and maintenance of axons and dendrites rather than for the formation of mitotic spindles. Recent studies from our laboratory sugge st that the mechanisms that organize the axonal and dendritic microtubule a rrays may be variations on the same mechanisms that organize the mitotic sp indle in dividing cells. In particular, we have identified molecular motor proteins that serve analogous functions in the establishment of these seemi ngly very different microtubule arrays. In the present study, we have sough t to determine whether a non-motor protein termed NuMA is also a component of both systems. NuMA is a similar to 230 kDa structural protein that is pr esent exclusively in the nucleus during interphase. During mitosis, NuMA fo rms aggregates that interact with microtubules and certain motor proteins. As a result of these interactions, NuMA is thought to draw together the min us-ends of microtubules, thereby helping to organize them into a bipolar sp indle. In contrast to mitotic cells, post-mitotic neurons display NuMA both in the nucleus and in the cytoplasm. NuMA appears as multiple small partic les within the somatodendritic compartment of the neuron, where its levels increase during early dendritic differentation. A partial but not complete colocalization with minus-ends of microtubules is suggested by the distribu tion of the particles during development and during drug treatments that al ter the microtubule array. These observations provide an initial set of clu es regarding a potentially important function of NuMA in the organization o f microtubules within the somatodendritic compartment of the neuron.