Regulation Of Proopiomelanocortin Messenger-rna Levels And Translation (in Situ, Hybridization, Stress, Dot Blot, Pituitary).

Proopiomelanocortin (POMC) is a large multipeptide precursor found in the anterior (AL) and intermediate lobes (IL) of the pituitary, the arcuate nucleus and the nucleus of the solitary tract. Secretion of POMC by pituitary cells is differentially regulated between the two lobes. The coordination of POMC mRNA levels with manipulations that alter release have been examined. Environmental stress, which produced parallel increases in POMC mRNA levels and plasma POMC peptides, was found to be a potent stimulator of both measures. Intermediate lobe melanotrophs were also found to respond to catecholaminergic stimuli by increasing POMC mRNA levels in response to dopamine antagonists and to beta-adrenergic agonists. These receptors were found to produce additive increases when ligands for both were administered together. A number of studies were performed to measure POMC translation/POMC mRNA levels and to determine if increased POMC mRNA levels were required to support increased POMC translation. Neither acute in vitro challenges or in vivo manipulations were effective in increasing POMC translational efficiency as a function of POMC mRNA. Two weeks of swim stress, which increased IL lobe POMC mRNA levels 3-fold, led to a decrease in translational efficiency, due perhaps to overloading of the ribosomes. In situ hybridization was performed to examine changes in POMC mRNA levels while retaining an anatomical context. Changes detected in IL POMC mRNA by in situ hybridization following administration of haloperidol paralleled those detected by blot hybridization. Resolution of single cells was also demonstrated in AL corticotrophs and in cells of the arcuate nucleus. These studies have demonstrated a coordination between POMC mRNA levels and secretory activity induced by environmental and pharmacological stimuli that are known to increase secretion of POMC peptides. This increase in POMC mRNA was shown in the IL to be necessary for increased translation of POMC which is required to replenish secreted peptides. This indicates that determination of mRNA levels can serve as an indicator of cellular response. In situ hybridization was shown to constitute a quantitative method for detecting changes in mRNA while retaining an anatomical context. This should prove useful in studying a heterogeneous tissue such as the brain.PhDBiological SciencesNeurosciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/127914/2/8621309.pd