MELATONIN RECEPTORS ARE FOR THE BIRDS - MOLECULAR ANALYSIS OF 2 RECEPTOR SUBTYPES DIFFERENTIALLY EXPRESSED IN CHICK BRAIN

Two receptors (CKA and CKB) of the G protein-coupled melatonin recepto r family were cloned from chick brain. CKA encodes a protein that is 8 0% identical at the amino acid level to the human Mel(1a) melatonin re ceptor and is thus designated the chick Mel(1a) melatonin receptor. CK B encodes a protein that is 80% identical to the Xenopus melatonin rec eptor and defines a new receptor subtype, the Moll, melatonin receptor , which is distinct from the Mel(1a) and Mel(1b) melatonin receptor su btypes. A melatonin receptor family consisting of three subtypes is su pported by PCR cloning of distinct melatonin receptor fragments from X enopus and zebrafish. Expression of CKA and CKB results in similar lig and binding and functional characteristics. The widespread distributio n of CKB and CKB mRNA in brain provides a molecular substrate for the profound actions of melatonin in birds.