Involved in the development and maintenance of excitatory synapse in the nervous system. Regulates surface expression of AMPA receptors and instructs the development of functional glutamate release sites. Acts as a ligand for the presynaptic receptors NRXN1-A and NRXN1-B. Interacts with DLG4 and NRXN1. Localized to excitatory synapses. Expressed in neuronal tissues. Widely distributed in neuropil regions in discrete puncta throughout the brain (at protein level). Detected in cortex, thalamus, striatum, olfactory bulb, cerebellum and all hippocampal subfields (at protein level). More abundant in deep than in superficial layers of neocortex (at protein level). Synaptogenic effects are mediated by the extracellular LRR region. Belongs to the LRRTM family.