Cell surface protein involved in cell-cell-interactions via its interactions with neurexin family members. Plays a role in synapse function and synaptic signal transmission, and probably mediates its effects by recruiting and clustering other synaptic proteins. May promote the initial formation of synapses, but is not essential for this. May also play a role in glia-glia or glia-neuron interactions in the developing peripheral nervous system. Interacts with NRXN1, NRXN2 and NRXN3. Interacts (via its C-terminus) with DLG4/PSD-95 (via PDZ domain 3) (By similarity). Homodimer, and heterodimer with NLGN1 and NLGN2 (By similarity). Detected at both glutamatergic and GABAergic synapses. Brain and arteries (at protein level). Detected in heart, brain, spleen, lung, liver, skeletal muscle, kidney and testis. Expressed in olfactory bulb and olfactory epithelium. Found in olfactory ensheathing glia but not in olfactory neurons, and in developing peripheral glia. Detected at embryonic day 17 dpc and postnatal day P1 in retinal astrocytes, spinal cord astrocytes and Schwann cells of the dorsal root ganglion. No obvious phenotype, but mice present subtle behavorial changes with reduced ultrasound vocalization and impaired response to olfactory cues. In addition, mice have reduced brain volume. Mice lacking both NLGN1 and NLGN3, or NLGN2 and NLGN3, are viable, but have impaired breathing, drastically reduced reproduction rates and striking deficits in raising their offspring. Mice lacking NLGN1, NLGN2 and NLGN3 are born at the expected Mendelian rate, but die shortly after birth due to respiratory failure. They do not show a significant change in the number of synapses, but synapse function is strongly impaired. Belongs to the type-B carboxylesterase/lipase family.