Interaction of Nogo-A with Nogo receptor. The interaction of Nogo-A (RTN4A) on oligodendrocytes and the Nogo receptor (NogoR) on neurons results in inhibition of axon regeneration after injury via Rho signaling [17,23,55,59,61-63,79]. The different regions of Nogo-A are colored as follows: red, 66-loop (Nogo66); green, Nogo-A-24; blue, Δ20. NogoR is in orange. The 66-loop interacts with NogoR to mediate growth-cone collapse and neurite outgrowth in vitro and to inhibit axon regeneration after injury [21,23,25,53,56,58,60,62]. The amino-terminal region Nogo-A-24 increases the binding affinity of Nogo-A to NogoR and also binds NogoR directly . The amino-terminal region Δ20 can mediate fibroblast and growth-cone collapse independently of NogoR . Some known co-receptors and signal transducers are listed beside the yellow symbol and are described in more detail in Table 1.