Axon Outgrowth & Guidance

The growth cone at the tip of an extending axon is exquisitely sensitive to repulsive and attractive guidance cues in its environment. These molecules may be diffusible and work from a distance, or may be bound to a membrane or substrate and work at close range. It is the complex integration of these repulsive and attractive signals that enhance or suppress axon outgrowth, and/or guide the axon to its appropriate target. These molecules play critical roles during nervous system development and may regulate the regeneration during nervous system disease.

The regenerative capacity of the injured adult central nervous system is limited. This may be due in part to inhibition by factors associated with myelin. Specifically, three myelin proteins including Nogo, Oligodendrocyte Myelin Glycoprotein, (OMgp), and Myelin-associated Glycoprotein (MAG) have been recognized as having the ability to suppress neurite outgrowth through their interaction with a receptor complex that contains the Nogo Receptor, NGF R/P75, and Lingo-1.

R&D Systems offers many research tools to study molecules involved in axon outgrowth and guidance. These include a broad selection of active proteins and specific antibodies designed for the ligands and receptors of several protein families including Ephrins/Ephs, Netrins, Semaphorins, Neurotrophins, Myelin-associated proteins, and more. Please visit our website at Neuroscience for a complete listing of our neuroscience-related products.

New: Recombinant Rat Nogo-A

Nogo-A is a member of the reticulon family of transmembrane proteins. This family is characterized by the presence of a non- signal sequence-containing N-terminus, a topologically conserved approximately 200 amino acid (aa) C-terminus that contains two transmembrane domains and an ER-retention motif. It exhibits a punctate intracellular distribution within the ER that is reminescent of a reticulum.1,2 Nogo-A in rat exists in four isoforms.3-5 The full length rat Nogo-A is 1163 aa in length and contains a 989 aa N-terminus, a 21 aa transmembrane segment, a 94 aa connecting loop, a second 21 aa transmembrane segment, and a 38 aa C-terminus (Figure 1). The exact topology of Nogo-A is unclear. With two transmembrane segments, the N- and C-termini may be extracellular with the loop region intracellular, or vice versa.6,7 Alternatively, the loop region and N-terminus may be on the same side of the membrane.8 Nogo-A is expressed in neurons, endothelial cells. oligodendrocytes, fibroblasts and myoblasts.9-11 Functionally, a 66 aa segment within the transmembrane connecting loop has been reported to bind to the GPI-linked Nogo receptor/p75 complex on axons to induce growth cone collapse,8,12,13 and aa segment 544-725 is reported to block neurite outgrowth.8,14

Figure 1. Schematic depicting the general structure of the rat Nogo-A polypeptide. The orientation of the protein in the cell membrane is currently unknown.

R&D Systems recombinant rat Nogo-A (Catalog # 2445-NG) is expressed as the 544-725 aa segment linked to the Fc region of human IgG in the murine myeloma cell line, NS0. The purified protein is a glycosylated disulfide-linked homodimer that exhibits inhibitory activity toward neurite outgrowth of cultured embryonic chick dorsal root ganglion cells (Figure 2).

Figure 2. Nogo-A inhibits neurite outgrowth. A. Embryonic chick dorsal root ganglion (DRG) cells exhibit neurite outgrowth when cultured on nitrocellulose-coated plates treated with laminin. B. Precoating similar plates with R&D Systems recombinant rat Nogo-A (Catalog # 2445-NG; 100 µg/mL) completely inhibits neurite outgrowth from embryonic chick DRG cells.


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  2. GrandPre, T. et al. (2000) Nature 403:439.
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  13. Wang, K.C. et al. (2002) Nature 420:74.
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