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* Department of Anatomy and Program in Neuroscience, The University of Wisconsin Medical School, Madison, Wisconsin
53706; The quintessential feature of the dendritic
microtubule array is its nonuniform pattern of polarity
orientation. During the development of the dendrite, a
population of plus end-distal microtubules first appears, and these microtubules are subsequently joined by a population of oppositely oriented microtubules.
Studies from our laboratory indicate that the latter microtubules are intercalated within the microtubule array by their specific transport from the cell body of the
neuron during a critical stage in development (Sharp,
D.J., W. Yu, and P.W. Baas. 1995. J. Cell Biol. 130:93- 104). In addition, we have established that the mitotic
motor protein termed CHO1/MKLP1 has the appropriate properties to transport microtubules in this manner
(Sharp, D.J., R. Kuriyama, and P.W. Baas. 1996. J. Neurosci. 16:4370-4375). In the present study we have
sought to determine whether CHO1/MKLP1 continues
to be expressed in terminally postmitotic neurons and
whether it is required for the establishment of the dendritic microtubule array. In situ hybridization analyses
reveal that CHO1/MKLP1 is expressed in postmitotic
cultured rat sympathetic and hippocampal neurons. Immunofluorescence analyses indicate that the motor is
absent from axons but is enriched in developing dendrites, where it appears as discrete patches associated
with the microtubule array. Treatment of the neurons
with antisense oligonucleotides to CHO1/MKLP1 suppresses dendritic differentiation, presumably by inhibiting the establishment of their nonuniform microtubule
polarity pattern. We conclude that CHO1/MKLP1
transports microtubules from the cell body into the developing dendrite with their minus ends leading,
thereby establishing the nonuniform microtubule polarity pattern of the dendrite.
Department of Cell Biology and Neuroanatomy, The University of Minnesota Medical School, Minneapolis, Minnesota
55455; and § Creative Biomolecules, Hopkinton, Massachusetts 01748
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