Microtubule polarity reversal accompanies regrowth of amputated neurites

Intact chicken sensory neurites have the same microtubule polarity reported for nongrowing axons in intact organisms. The assembly-favored or + ends of the microtubules are found at the distal terminal (growth cone) of the neuron. After amputation of chicken sensory neurites, the fragment removed from the cell body collapsed to a bead of axoplasm from which neurites rapidly regrew. In nine such regrown neurites analyzed for microtubule polarity, the + ends of microtubules faced the newly formed growth cones, i.e.,--ends of microtubules were now at the original distal terminal of the neuron. These results indicate that microtubules reorganized concomitant with neurite regrowth to form a uniformly polar microtubule array but with reversed polarity. This suggests that mechanisms within the neurite, independent of the cell body, are sufficient for organization of microtubule assembly during axonal elongation. Our data also indicate that microtubule + ends were correlated with growth cone formation in the following three experimental classes of neurites: normal, regrown, and amputated but extended. We speculate that + ends of microtubules are a requirement for growth cone formation and advance.