SEGMENTED PATTERN OF TYROSINATED MICROTUBULES ASSEMBLY IN NEURITES OFCHICK-RETINAL NEURONS

The sites of microtubule assembly in neurites of cultured chick retina l neurons were assessed by double indirect immunofluorescence using an tibodies specific for tyrosinated and detyrosinated tubulin. Tyrosinat ed microtubules were distributed all over the neuron while detyrosinat ed microtubules were found only in long neurites. When cultures were i ncubated with nocodazole, the tyrosinated but not the detyrosinated mi crotubules were disassembled. The sites of appearance of tyrosinated m icrotubules after a reversible depolymerization by nocodazole were exa mined in neurons bearing one unique and long neurite. One minute after releasing the drug, tyrosinated microtubules quickly appeared as a sh ort segment at the neurite tip and as spots periodically distributed a long the neurite length. At longer times, the tyrosinated microtubules depicted a segmented pattern along the neurite reaching a continuous pattern at about 60 min. Our results suggest that the neurite cytoskel eton is composed by microtubules of low (detyrosinated) and high (tyro sinated) dynamism. Dynamic tyrosinated microtubules could be formed al ong the entire length and at the tip of the axon-like neurite using de tyrosinated microtubules as primers.