Melatonin receptors are for the birds: Molecular analysis of two receptor subtypes differentially expressed in chick brain

Abstract

Two receptors (CKA and CKB) of the G protein-coupled melatonin receptor family were cloned from chick brain. CKA encodes a protein that is 80% identical at the amino acid level to the human Mel1a melatonin receptor and is thus designated the chick Mel1a melatonin receptor. CKB encodes a protein that is 80% identical to the Xenopus melatonin receptor and defines a new receptor subtype, the Mel1c melatonin receptor, which is distinct from the Mel1a and Mel1b melatonin receptor subtypes. A melatonin receptor family consisting of three subtypes is supported by PCR cloning of distinct melatonin receptor fragments from Xenopus and zebrafish. Expression of CKA and CKB results in similar ligand binding and functional characteristics. The widespread distribution of CKA and CKB mRNA in brain provides a molecular substrate for the profound actions of melatonin in birds.

Cloning of a melatonin‐related receptor from human pituitary

“…Recently, a family of G protein-coupled melatonin receptors have been cloned from Xenopus laevis, chickens and mammals [2][3][4][5]. These recombinant receptors exhibit similar affinity and pharmacological characteristics to each other and to endogenous receptors, as defined with the melatonin agonist 2-[l~5I]iodomelatonin ([125I]Mel).…”

Melatonin induces the expression of gonadotropin-inhibitory hormone in the avian brain

“…Recent molecular studies (19,29) have led to the identification of three avian melatonin receptor subtypes, Mel 1a , Mel 1b , and Mel 1c , which comprise a distinct subfamily within the superfamily of G-protein-coupled receptors. Because Mel 1c mRNA is differentially expressed in the chicken hypothalamus (19), quail Mel 1c cDNA was cloned and used for in situ hybridization of Mel 1c mRNA, which was combined with GnIH immunocytochemistry. The GnIH antiserum recognized PVN neurons that were positively stained by in situ hybridization of Mel 1c mRNA, providing strong evidence that GnIH neurons in the PVN express Mel 1c in the quail.…”

Melatonin Receptor Expression in the Zebra Finch Brain and Peripheral Tissues

“…Chicken Mel1A is 80% identical to human Mel1A (Reppert et al 1995) and is the structural homolog of the mammalian MT1 receptor. Chicken Mel-1C receptor has an 80% homology to the Mel-1C found in Xenopus, and is 60% identical to the mammalian Mel-1A and -1B receptors (Reppert, 1997;Reppert et al 1995). Mel-1C of lower vertebrates has an MT1-like pharmacology and receptor distribution suggests that melatonin may exert temporal control over a broad range of physiological and behavioural events in birds (Reppert et al, 1995;Sugden et al 2004).…”

“…The main differences between the membrane receptor types are their kinetic and pharmacological properties for melatonin and its agonists: Mel-1A is a high affinity binding receptor, whereas the Mel-1B receptor has a low affinity for binding (Dubocovich 1995). Chicken Mel1A is 80% identical to human Mel1A (Reppert et al 1995) and is the structural homolog of the mammalian MT1 receptor. Chicken Mel-1C receptor has an 80% homology to the Mel-1C found in Xenopus, and is 60% identical to the mammalian Mel-1A and -1B receptors (Reppert, 1997;Reppert et al 1995).…”

“…Chicken Mel-1C receptor has an 80% homology to the Mel-1C found in Xenopus, and is 60% identical to the mammalian Mel-1A and -1B receptors (Reppert, 1997;Reppert et al 1995). Mel-1C of lower vertebrates has an MT1-like pharmacology and receptor distribution suggests that melatonin may exert temporal control over a broad range of physiological and behavioural events in birds (Reppert et al, 1995;Sugden et al 2004). Mel-1C has rapidly evolved from fishes and birds to mammals to the so-called GPR50 receptor that is believed to act as a modulator of melatonin responsiveness (Dufourny et al, 2008).…”