Article

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

Laboratory of Developmental Chronobiology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Neuron (Impact Factor: 15.98). 12/1995; 15(5):1003-15. DOI: 10.1016/0896-6273(95)90090-X
Source: PubMed

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.

1 Follower
 · 
79 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Melatonin receptor gene expression as well as melatonin synthesis and secretion activities were examined in the pineal gland of the grass puffer, which exhibits unique lunar/tidal cycle-synchronized mass spawing: spawning occurs before high tide on the day of spring tide during spawing season. Melatonin synthesizing activity was assessed by the abundance of arylalkylamine N-acetyltransferase 2 (AANAT2) mRNA. The amount of aanat2 mRNA was low during light phase and initiated to increase after the light was turned off. The secretion of melatonin from primary pineal organ culture was stimulated after the light was turned off and ceased immediately after the light was turned on. The expression levels of four melatonin receptor subtype genes (mel 1a 1.4, mel 1a 1.7, mel1b, and mel1c) showed synchronous variations, and the levels tended to be high during the dark phase under light/dark conditions. These results suggest that the action of melatonin on the pineal gland is highly dependent on light and photoperiod, possibly with stronger action during night time. Under constant darkness, the expression of four melatonin receptor subtype genes showed unique ultradian oscillations with the period of 14.0-15.4 h, suggesting the presence of a circatidal oscillator in the pineal gland. The present results indicate that melatonin may serve local chronobiological functions in the pineal gland. These cyclic expressions of melatonin receptor genes in the pineal gland may be important in the control of the lunar/tidal cycle-synchronized mass spawning in the grass puffer.
  • Canadian Journal of Animal Science 09/2014; 94(3):391-400. DOI:10.4141/cjas2013-177 · 0.98 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Three primitive photoreceptors [melanopsin (Opn4), neuropsin / opsin5 (Opn5) and vertebrate ancient opsin (VAOpn)] were reported as possible avian deep-brain photoreceptors (DBPs) involved in the perception of photoperiodic information affecting the onset and development of reproduction. The objective of this study was to determine the effect of long-day photostimulation and/or sulfamethazine treatment (SMZ, a compound known to advance light-induced testes development) on gene expression of DBPs and key hypothalamic and pituitary genes involved in avian reproductive function. Two-week old chicks were randomly selected into four experimental groups: short-day control (SC, LD8:16), short-day + SMZ (SS, LD8:16, 0.2% diet SMZ), long-day control (LC, LD16:8), and long-day + SMZ (LS, LD16:8, 0.2% diet SMZ). Birds were sampled on days 3, 7, and 28 after initiation of a long-day photoperiod and/or SMZ dietary treatments. Three brain regions [septal-preoptic, anterior hypothalamic (SepPre/Ant-Hypo) region, mid-hypothalamic (Mid-Hypo) region, posterior-hypothalamic (Post-Hypo) region], and anterior pituitary gland were dissected. Using quantitative real-time RT-PCR, we determined changes of expression levels of genes in distinct brain regions; Opn4 and Opn5 in SepPre/Ant-Hypo and Post-Hypo regions and, VAOpn in the Mid-Hypo region. Long-day treatment resulted in a significantly elevated testes weight on days 7 and 28 compared to controls, and SMZ augmented testes weight in both short- and long-day treatment after day 7 (P < 0.05). Long-day photoperiodic treatment on the third day unexpectedly induced a large 8.4 fold increase of VAOpn expression in the Mid-Hypo region, a 15.4 fold increase of Opn4 and a 97.8 fold increase of Opn5 gene expression in the Post-Hypo region compared to SC birds (P < 0.01). In contrast, on days 7 and 28, gene expression of the three DBPs was barely detectable. LC group showed a significant increase in GnRH-1 and TRH mRNA in the Mid-Hypo compared to SC on day 3. Pituitary LHβ and FSHβ mRNA were significantly elevated in LC and LS groups compared to SC on days 3 and 7 (P < 0.05). On days 3 and 7, TSHβ mRNA level was significantly elevated by long-day treatment compared to the SC groups (P < 0.05). Results suggest that long-day photoperiodic activation of DBPs is robust, transient, and temporally related with neuroendocrine genes involved in reproductive function. Additionally, results indicate that two subsets of GnRH-1 neurons exist based upon significantly different gene expression from long-day photostimulation and long-day plus SMZ administration. Taken together, the data indicate that within three days of a long-day photoperiod, an eminent activation of all three types of DBPs might be involved in priming the neuroendocrine system to activate reproductive function in chickens. Copyright © 2014. Published by Elsevier Inc.
    General and Comparative Endocrinology 12/2014; 211. DOI:10.1016/j.ygcen.2014.11.020 · 2.67 Impact Factor

Full-text

Download
12 Downloads
Available from
Feb 5, 2015