CYTOSKELETAL CHANGES DURING NEUROGENESIS IN CULTURES OF AVIAN NEURAL CREST CELLS

Neural crest cells are motile and mitotic, whereas their neuronal deri vatives are terminally post-mitotic and consist of stationary cell bod y from which processes grow. The present study documents changes in th e cytoskeleton that occur during neurogenesis in cultures of avian neu ral crest cells. The undifferentiated neural crest cells contain dense bundles of actin filaments throughout their cytoplasm, and a splayed array of microtubules attached to the centrosome. In newly differentia ting neurons, the actin bundles are disrupted and most of the remainin g actin filaments are reorganized into a cortical layer underlying the plasma membrane of the cell body and processes. Microtubules are more abundant in newly-differentiating neurons than in the undifferentiate d cells, and individual microtubules can be seen dissociated from the centrosome. Neuron-specific beta-III tubulin appears in some crest cel ls prior to cessation of motility and cell division, and expression in creases with total microtubule levels during neurogenesis. To investig ate how these early cytoskeletal changes might contribute to alteratio ns in morphology during neurogenesis, we have disrupted the cytoskelet on with pharmacologic agents. Microfilament disruption by cytochalasin immediately arrests the movement of neural crest cells and causes the m to round-up, but does not significantly change the morphology of the immature neurons. Microtubule depolymerization by nocodazole slows th e movement of undifferentiated cells and causes retraction of processe s extended by the immature neurons. These results suggest that changes in the actin and microtubule arrays within neural crest cells govern distinct aspects of their morphogenesis into neurons.