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Title: Regulation of gene expression by melatonin in the ovine pituitary
Author: Ross, A. W.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1996
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In pars tuberalis cells of the ovine pituitary, melatonin inhibits forskolin-stimulated increases in cyclic AMP, and protein kinase A. In this study, proteins which bind a CRE have been detected and supershifted with antiCREB antibodies. Following phosphorylation with PKAc, the CRE-binding proteins were supershifted by antiP-CREB antibodies, indicating that these are probably endogenous PKA substrates. Western blotting with antiP-CREB detected increased intensities of proteins, thought to be CREB and ATF-1, in response to forskolin. Melatonin reversed these increases suggesting that melatonin may influence the phosphorylation state and hence, transcription activating potential for these factors. Subsequently, mRNA levels of cyclic AMP-responsive c-fos (and c-Fos protein levels) and junB immediate early genes were shown to be stimulated by forskolin and these responses were inhibited by melatonin. Other AP-1 genes tested, c-jun and junD, were neither stimulated by forskolin, nor inhibited by melatonin. PMA dramatically induced c-fos, and importantly, melatonin inhibited this response, possibly by functioning through a novel cyclic AMP-independent pathway previously not known to be linked to the melatonin receptor. These results demonstrate that melatonin can communicate to the PT cell nucleus to influence mRNA levels, probably by regulating transcription factor activities. By differential display, followed by product sequencing, the forskolin-induced c-fos expression was confirmed. Egr-1 induction, detected after PT stimulation with forskolin, was not responsive to melatonin. Expression of several late response genes increased over 24 hours of forskolin stimulation; one was inhibited by melatonin. Cloning, sequencing and library screening produced a 1301bp fragment of this gene which appeared as a 4kb band by Northern blotting. Melatonin responsiveness suggests a PT-specific function for the product of this gene.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available