Member of the repulsive guidance molecule (RGM) family that contributes to the patterning of the developing nervous system. Acts as a bone morphogenetic protein (BMP) coreceptor that potentiates BMP signaling. Promotes neuronal adhesion. May inhibit neurite outgrowth (By similarity). Homooligomer. Interacts with DRGX. Interacts with BMP2 and BMP4. Interacts with the BMP type I receptors ACVR1, BMPR1A and BMPR1B and with the BMP type II receptor ACVR2B. The functional complex with its receptor NEO1/neogenin appears to be a heterotetramer with a 2:2 stoichiometry, RGM molecules acting as staples that bring two NEO1 receptors together without interacting themselves, this arrangement leads to activation of downstream signaling via RhoA. Detected in neonatal and adult dorsal root ganglion sensory neurons, spinal cord, and brain (at protein level). Also expressed at high levels in retinal ganglion cells of developing mouse, extending to the optic nerve (at protein level). Expressed in testis, epididymis, ovary, uterus, and pituitary. Expressed in the developing nervous system. Expression is restricted to a subset of individual neurons in the mid- and hindbrain regions. At 10.5 dpc, expression level increases and extends further into the forebrain. The segmented pattern of expression becomes more refined and is indicative of peripheral nervous system labelling. Not detected in the area of motoneuron differentiation. Expression could be restricted to postmitotic neurons. Also expressed in fetal dorsal root ganglion, dorsal horn, in the dorsomedial mantle layer of the spinal cord, alar plate of the myelencephalon, marginal layer of the mesencephalon, basal plate of the pons, and cerebellar primordia, as well as the cortex of the olfactory lobe, retina, and olfactory epithelium. In the developing eye, expressed in differentiating ganglion cells and later in the development, also in amacrine cells. In adult, expressed in scattered cells throughout the brain. GPI-anchored. Autocatalytically cleaved at low pH; the two chains remain linked via two disulfide bonds. Belongs to the repulsive guidance molecule (RGM) family.