Plays a role in targeting the monocarboxylate transporters SLC16A1 and SLC16A7 to the cell membrane (By similarity). Plays a role in the outgrowth of motoneurons and in the formation of neuromuscular junctions. Following muscle denervation, promotes nerve terminal sprouting and the formation of additional acetylcholine receptor clusters at synaptic sites without affecting terminal Schwann cell number or morphology. Delays the retraction of terminal sprouts following re-innervation of denervated endplates. Interacts with SLC16A1 and SLC16A7. Localizes to the neuromuscular junctions. Only member of the immunoglobulin superfamily to be expressed in embryonal carcinoma cells, which resemble multipotential cells of early embryos. At neuromuscular junctions, 5-fold higher expression levels at P0 compared to adult. Regulated by muscle activity. Strongly up-regulated after muscle denervation, including that of gastrocnemius muscle. Maximal expression is observed 10 days after denervation (at protein level).