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Title: Investigation of signal transduction by human melatonin receptors
Author: Brydon, L.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1999
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Melatonin acts through G protein-coupled receptors to mediate a variety of circadian and seasonal responses in mammals, including changes in body weight. The results of this thesis demonstrate that the Mel1b melatonin receptor subtype, coupled to an inhibition of the cGMP pathway is present in human brown adipocytes. This would suggest that melatonin may have a direct action on adipocytes and may thus play a role in the development and energy expenditure of this tissue. To gain further insight into the molecular mechanisms of melatonin action, a polyclonal antibody specific for the human Mel1a receptor was developed. Using this antibody, the Mel1a melatonin receptor was demonstrated to selectively couple to Gi2, Gi3 and Gq/11 proteins in HEK293 cells stably expressing the human Mel1a receptor. Coupling to Gi2/3 leads to an inhibition of adenylate cyclase, whilst coupling to Gq/11 explains a PTX-insensitive melatonin induced elevation of cytosolic calcium in these HEK293 cells. Melatonin-induced cytosolic calcium mobilization was further confirmed in primary cultures of ovine pars tuberalis cells endogenously expressing Mel1a receptors. Immunoprecipitation experiments also revealed that the Mel1a receptor couples to G proteins in the absence of agonist and this coupling is resistant to treatment with GTP analogues and pertussis toxin. This suggests that melatonin receptors form a very tight pre-coupled complex which may explain constitutive activity of the Mel1a receptor in the Golgi apparatus in several cell lines stably expressing this receptor. The significance of this observation needs to be established, but may be related to the ability of the melatonin receptor to record time as duration of melatonin secretion from the pineal gland.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available