Melatonin receptor 1A (MTNR1A) is one of two high affinity forms of a receptor for melatonin, the primary hormone secreted by the pineal gland. This receptor is a G-protein coupled, 7-transmembrane receptor that is responsible for melatonin effects on mammalian circadian rhythm and reproductive alterations affected by day length. MTNR1A is an integral membrane protein that is readily detectable and localized to two specific regions of the brain. The hypothalamic suprachiasmatic nucleus appears to be involved in circadian rhythm while the hypophysial pars tuberalis may be responsible for the reproductive effects of melatonin. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804