Axonal transport of the cytoplasmic matrix.

Abstract

The cytoplasmic matrix is often highly specialized, making it possible to clearly relate particularaspects ofthe cytoplasmic matrix to the specialized functions of cells . For example, in striated muscle cells the contractile components of the cytoplasmic matrix dominate the cell structurally and functionally. Neurons are another example of cells in which specializations of structure and function can be clearly related to particular aspects of the cytoplasmic matrix (36, 37) . The primary function of neurons is to convey information from one location in the organism to another. Pathways for information transfer in the nervous system are provided by specialized neuronal extensions, the axons and the dendrites . Axons, in particular, are specialized to convey information over very long distances, meters in some cases . Accordingly, in the axon the cytoplasmic matrix is specialized to generate and support the extremely elongate shape ofthe axon during development, regeneration, and maturity. To generate and maintain the great volume of cytoplasm within the axon, neurons must produce tremendous amounts of protein (32) . Essentially all axonal proteins are synthesized in the neuron cell body and then conveyed into the axon by axonal transport, which provides a lifeline for the axon and its terminus (25, 36) . Axonal transport is a process that is initiated when the axon first develops and that continues throughout the life of the neuron . To meet the needs of large animals, which require long axons, axonal transport has become one of the most highly developed mechanisms for the intracellular transport of materials in metazoan cells .