A New Strategy for Studying Microtubule Transport and Assembly During Axon Growth

Abstract

There is widespread agreement that the net addition of new microtubule polymer to the axon is necessary for its growth, but there is controversy concerning the mechanisms by which this occurs. The earliest model held that preassembled microtubules are transported from the cell body of the neuron down the growing axon, while subsequent models held that new polymer is added at the distal region of the growing axon via local microtubule assembly. Since these early models were proposed, many workers have taken the view that microtubule transport and assembly events are mutually exclusive, and hence that evidence supporting one model refutes the other. We have taken a very different view, that microtubule transport and assembly are both important during axon growth. In our model, microtubule transport is required to increase the tubulin levels within the axon, and local assembly events are required to regulate the lengths of the microtubules (for review see Baas and Yu 1996).