In normal brain development, oligodendrocytes
are responsible for regulating axonal growth via the Nogo protein and
its receptor, Nogo receptor (NgR). Nogo binds to the leucine-rich repeat
(LRR) domains of NgR and facilitates the inhibition of axon growth [4].
There are a number of co-receptors that signal with NgR on the axonal
membrane including Lingo-1 as a co-factor [5–7]. Since NgR itself
does not contain a transmembrane domain, it requires a transmembrane
co-receptor in order to elicit intracellular signals. NgR contains a
glycosylphosphatidylinositol-anchored-ligand-binding subunit which
binds with either the p75 neurotrophin receptor or Tumor necrosis factor
Receptor Orphan Y (TROY). The resulting trimolecular NgR receptor
complex activates RhoA a small GTP-binding protein, subsequently
setting off a cascade of intracellular molecular events resulting in the
collapse of growth cones, thus preventing further growth by the axon,
and the inhibition of myelination