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 .

Neurofilaments at a glance

“…The earliest in vivo pulse-labeling studies of neurofilament protein transport by Lasek and colleagues were initially interpreted to support the idea that the labeled neurofilaments that undergo transport constitute the entire NF cytoskeleton within axons, which, according to this model, is continuously moving (Lasek et al, 1984;Lasek et al, 1992). A different model, however, was proposed by the authors on the basis of studies of short and exceptionally long-term (6 months) pulse-labeling by using the mouse optic system (Nixon and Logvinenko, 1986).…”

Cytoskeletal Requirements in Axonal Transport of Slow Component-b

“…SCb moves at average rates of 2-8 mm/d and transports Ϸ200 proteins, of which only a handful have been identified. Among these are myosin, dynein, clathrin, calmodulin, synapsin, ␣-synuclein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), superoxide dismutase-1, phosphofructokinase, ubiquitin, molecular chaperones, tau and other microtubule-associated proteins (MAPs), spectrin, actindepolymerizing factor, and actin (Willard et al, 1974;Black and Lasek, 1979;Brady et al, 1981;Garner and Lasek, 1982;Lasek et al, 1984;Baitinger and Willard, 1987;Nixon et al, 1990;Bray et al, 1992;Mercken et al, 1995;Dillman et al, 1996;Yuan et al, 1999;Ma et al, 2000;Bourke et al, 2002;Li et al, 2004). Clearly, the proteins of SCb are functionally diverse, play critical roles in maintaining the integrity of axons and synapses, and are implicated in neurodegenerative diseases .…”

Rotational dynamics of cargos at pauses during axonal transport

“…The underlying mechanism of axonal transport has been studied intensively for several decades [3][4][5][6][7][8] . Cargos are moved between the cell body and the synapse via fast and slow axonal transport.…”