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Title: Proopiomelanocortin expression and processing in the ovine pars intermedia
Author: Richardson, Matthew Paul
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2000
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This thesis describes studies into the effect of season and photoperiod on the aMSH-synthetic activity of the pars intermedia in the highly photoperiodically-responsive Soay sheep. The influence of the hypothalamus and dopaminergic inhibition was also studied. The localisation and expression of POMC mRNA, POMC-derived peptides and both PC1 and PC2 mRNAs and proteins were measured by in situ hybridisation. RNase protection assay and immunocytochemistry; specific riboprobes were developed for the project. The presence of the cellular proliferation marker, PCNA, was used as an index of cellular proliferation. In the first study, the general anatomy of the ovine pituitary gland was investigated using the new methodology. POMC mRNA was highly expressed in melanotrophs in the pars intermedia and in the corticotrophs dispersed in the pars distalis. The POMC-derived peptides, ACTH and aMSH both occurred in the pars intermedia while in the pars distalis ACTH predominated and aMSH was only weakly expressed. PC1 mRNA and protein was also expressed both in the pars distalis and the pars intermedia with a distribution similar to that of POMC, as well as in the pars nervosa. PC2 mRNA was expressed in the pars intermedia while PC2 protein occurred principally in the pars intermedia and pars nervosa. Like aMSH, PC2 protein was expressed weakly in the pars distalis. The second study investigated the changing activity of the pars intermedia at four seasonal time points in the Soay ewes living outdoors and exposed to natural photoperiod (n=5/group). Expression of POMC and PC1 mRNA was significantly greater in the summer and autumn compared to the winter and spring. The autumnal increase in pars intermedia activity was also characterised by an increase in cellular proliferative activity and hypertrophy of melanotrophs.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available