Analysis of microtubules in isolated axoplasm from the squid giant axon.

Biochemical specialization of cellular microtubules has emerged as a primary mechanism in specifying microtubule dynamics and function. However, study of specific subcellular populations of cytoplasmic microtubules has been limited, particularly in the nervous system. The complexity of nervous tissue makes it difficult to distinguish neuronal microtubules from glial microtubules, and axonal microtubules from dendritic and cell body microtubules. The problem is further compounded by the finding that a large fraction of neuronal tubulin is lost during standard preparations of brain tubulin, and this population of stable microtubules is enriched in axons. Here, we consider a unique biological model that provides a unique opportunity to study axonal microtubules both in situ and in vitro: isolated axoplasm from the squid giant axon. The axoplasm model represents a powerful system for addressing fundamental questions of microtubule structure and function in the axon.