Changes in membrane trafficking and actin dynamics during axon formation in cultured hippocampal neurons

Neurons begin to polarize when one of the neurites becomes the axon. Hippoc ampal neurons in cell culture have a sharp transition between their unpolar ized and polarized stage revealed by the rapid growth of the future axon. R ecent progress shows that both a cytoplasmic membrane flow and actin dynami cs govern axon formation, and thereby initial neuronal polarization. We her e review these mechanisms, evaluate their physiological role, and show simi larities to the transient polarization of migrating fibroblasts. Finally, w e present a model how actin dynamics and vectorial membrane flow may intera ct to achieve axon formation. (C) 2000 Wiley-Liss, Inc.