Neuronal Growth Regulator 1, NEGR1, also known as neurotractin, or KILON, belongs to the immunoglobulin superfamily, IgLON family. This GPI-linked cell surface glycoprotein NEGR1 is composed of three Ig-like domains and belongs to the IgLON subgroup of neural IgSF members. It is expressed in two isoforms with apparent molecular masses of 50 and 37 kD, termed L-form and S-form, respectively. NEGR1/Neurotractin participates in the regulation of neurite outgrowth in the developing brain and is expressed on the neurites of primary hippocampal neurons. Neurotractin/KILON is a trans-neural growth-promoting factor for outgrowing axons following hippocampal denervation. KILON (kindred of IgLON) and opioid-binding cell adhesion molecule, together with the limbic system-associated membrane protein and neurotrophin, belong to the IgLON subgroup of immunoglobulin superfamily. The alteration of the modulatory function of KILON/NEGR1 for the number of dendritic synapses concomitant with changes in its localization and detergent solubility during neuronal culture development. In addition to its reported role in the brain, NEGR1 is also expressed in subcutaneous adipose tissue and acts as a central 'hub' in an obesity-related transcript network.