Reticulon-4, also known as Foocen, Neurite outgrowth inhibitor, Nogo protein, Neuroendocrine-specific protein, Neuroendocrine-specific protein C homolog, RTN-x, Reticulon-5 and RTN4, is a multi-pass membrane protein which contains onereticulon domain. Isoform1of RTN4 is specifically expressed in brain and testis and weakly in heart and skeletal muscle. Isoform2 of RTN4 is widely expressed except for the liver. Isoform3of RTN4 is expressed in brain, skeletal muscle and adipocytes. Isoform4of RTN4 is testis-specific. Reticulon-4 / RTN4 is a developmental neurite growth regulatory factor with a role as a negative regulator of axon-axon adhesion and growth, and as a facilitator of neurite branching. Reticulon-4 / RTN4 regulates neurite fasciculation, branching and extension in the developing nervous system. Reticulon-4 / RTN4 is involved in down-regulation of growth, stabilization of wiring and restriction of plasticity in the adult CNS. It regulates the radial migration of cortical neurons via an RTN4R-LINGO1 containing receptor complex. Isoform 2 of RTN4 reduces the anti-apoptotic activity of Bcl-xl and Bcl-2. This is likely consecutive to their change in subcellular location, from the mitochondria to the endoplasmic reticulum, after binding and sequestration. Isoform 2 and isoform 3 of RTN4 inhibit BACE1 activity and amyloid precursor protein processing.