| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2000: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 1999: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Research Abstract |
Cell polarity provides a basis for the complex morphology of neurons. The mechanisms for the establishment and maintenance of cell polarity in neurons are not well understood. Banker G.and colleagues have reported that polarity is altered when the axon is cut in hippocampal neurons in vitro ; another immature neurite subsequently develops into an axon. It is not known, however, whether mature dendrites in vivo are still able to change their identity. To examine this possibility, we isolated and cultured neurons from neonatal rat brain. With mild pipetting of cerebral cortex following trypsinization, we obtained neurons that each possessed a long and thick process. This process had a tapering structure, contained the Golgi complexes, was immunoreactive to anti-MAP2ab antibody, and was therefore identified as a dendrite. We monitored the regeneration of this dendrite for three days in culture. In 77% of observed neurons, novel axons, as identified by positive immunoreactivity to dephosphorylated tau or by negative immunoreactivity to MAP2ab, appeared to have formed from the original dendrite. Closer observation of such cases revealed that the distal half of the original dendrite became dephosphorylated tau-positive or MAP2ab-negative. Time lapse video microscopy followed by immunostaining disproved the possibility that the original dendrite retracted and that a novel axon was generated from the stump. These results indicate the conversion of a dendrititic cytoskeleton into an axonal one. Our study shows that the polarity of neurons, once established in vivo can be altered when neurons are isolated. The alteration of polarity is often coupled with the conversion of dendrites into axons.
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