Involved in the initial immune cell clustering during inflammatory response and may regulate chemotactic activity of chemokines (By similarity). May play a role in melanocortin signaling pathways that regulate energy homeostasis and hair color. Low-affinity receptor for agouti (By similarity). Has a critical role in normal myelination in the central nervous system. Monomer and homotrimer. Heavily glycosylated. Defects in Atrn (isoform 1) are the cause of the autosomal recessive phenotype zitter (zi), which is characterized by progressive hypomyelination and vacuolation in the central nervous system resulting in early-onset tremor and progressive flaccid paresis of the hind limb. This is due to an 8-bp deletion at the splice donor site of intron 12, which results in aberrant and unstable transcripts.