Axonally Transported Proteins in Axon Development, Maintenance, and Regeneration

Abstract

The static beauty of the structure of an axon belies its dynamic nature. An axon typically comprises a scaffolding of linear elements, the microtubules and neurofilaments, that are connected to each other and to the plasma membrane by a lattice of cross-linkers (Fig. 1). Embedded in this lattice, and communicating with the linear elements by additional cross-linkers, are membrane-bounded organelles (mitochondria and a variety of vesicular organelles). Smooth endoplasmic reticulum and F-actin microfilaments are often most concentrated beneath the axolemma. This picture of the axon represents the steady state of a system whose components are, in fact, in rapid flux. To appreciate the dynamic nature of the axon at a molecular level, the metabolic polarity of the axon can be exploited. Because the