Molecular dissection of the myelin-associated glycoprotein receptor complex reveals cell type–specific mechanisms for neurite outgrowth inhibition

Neuronal Nogo66 receptor-1 (NgR1) binds the myelin inhibitors NogoA, OMgp, and myelin-associated glycoprotein (MAG) and has been proposed to function as the ligand-binding component of a receptor complex that also includes Lingo-1, p75^NTR, or TROY. In this study, we use Vibrio cholerae neuraminidase (VCN) and mouse genetics to probe the molecular composition of the MAG receptor complex in postnatal retinal ganglion cells (RGCs). We find that VCN treatment is not sufficient to release MAG inhibition of RGCs; however, it does attenuate MAG inhibition of cerebellar granule neurons. Furthermore, the loss of p75^NTR is not sufficient to release MAG inhibition of RGCs, but p75^NTR−/− dorsal root ganglion neurons show enhanced growth on MAG compared to wild-type controls. Interestingly, TROY is not a functional substitute for p75^NTR in RGCs. Finally, NgR1^−/− RGCs are strongly inhibited by MAG. In the presence of VCN, however, NgR1^−/− RGCs exhibit enhanced neurite growth. Collectively, our experiments reveal distinct and cell type–specific mechanisms for MAG-elicited growth inhibition.