May function as an output molecule from the suprachiasmatic nucleus (SCN) that transmits behavioral circadian rhythm. May also function locally within the SCN to synchronize output. Potently contracts gastrointestinal (GI) smooth muscle (By similarity). Expressed in the SCN and among a few other discrete brain areas, including the islands of Calleja, media l preoptic area of the hypothalamus and the shell of the nucleus accumbens. Highly expressed in testis. In the SCN, expression subjected to high amplitude of circadian oscillation. Expressed in mid-late pachytene spermatocytes at the stages VII, VIII and IX of the semiferous epithelial cycle. Activated by CLOCK and BMAL1 heterodimers and light; inhibited by period genes (PER1, PER2 and PER3) and cryptochrome genes (CRY1 and CRY2). Belongs to the AVIT (prokineticin) family.