Submitted to: Journal of Biological Chemistry
Publication Type: Abstract Only
Publication Acceptance Date: August 4, 1999
Publication Date: N/A
Interpretive Summary: In recent years a better understanding of the factors regulating food intake and appetitite in mammals has been gained. This information was boosted by the discovery of a hormone secreted by fat cells, termed leptin, which was subsequently shown to be an important component to food intake regulation and energy expenditure. This study was conducted to clone the leptin gene in chickens and to determine the effect of various hormones on leptin gene expression in the chicken to gain a better understanding of factors influencing leptin gene epression in birds. The results of this study showed that the chicken leptin gene is 90% identical to rat leptin and moret than 80% similar to other mammalian leptins, and that the leptin gene is expressed in both liver and fat tissue. We also demonstrated for the first time that the leptin gene is expressed by the chick embryo and yolk sac membrane, indicating that leptin has a role in embryonic development. It was also found that leptin gene expression is up-regulated by insulin and an adrenal hormone, and down-regulated by glucagon and estrogen. Liver and fat tissue leptin gene expression were differentially affected by the hormones. In conclusion, the results of this study suggests that the site and degree of leptin expression observed in chickens may be due to differences between birds and mammals in lipid metabolism.
Expression of proadrenomedullin-derived peptides in the rat, cow and human pituitary was studied by a variety of techniques. Immunocytochemical detection showed a widespread expression of adrenomedullin (AM) peptide in the adenohypophysis and the neural lobe, with low expression in the pars intermedia. ProAM N-20 terminal peptide (PAMP) immunoreactivity was present tin the anterior pituitary but showed a more marked heterogenous distribution, with cells staining from very strong to negative. Lower levels of PAMP staining were found in the neural lobes. Paraffin and semin- thin serial sections immunostained against PAMP and the traditional pituitary hormones revealed that a subpopulation of the gonadotropes expressed high levels of PAMP peptide. Ultrastructural analysis clearly showed PAMP immunoreactivity in the FSH containing large secretory granules of the gonadotropees, suggesting simultaneous secretion of PAMP and FSH by this cell type. Three mouse cell pituitary lines (AtT20, GH3 and aT3-1) respectively derived from corticotropes, somatolactotropes, and gonadotropes were also analyzed and showed expression of both PAMP-derived peptides and their mRNAs. Collectively, our data support that PAMP-derived peptides are expressed in the pituitary in a cell specific pattern, with post-translational processing as a possible mechanism of regulation of secretion. Data showing the co-localization of PAMP and FSH in the same secretory granules open a way by which PAMP could intervene in the control of reprodcutive physiology in a coordinated fashion with FSH.