Submitted to: BARC Poster Day
Publication Type: Abstract only
Publication Acceptance Date: 4/25/2005
Publication Date: 5/12/2005
Citation: Poch, S.M., Richards, M.P., McMurtry, J.P. 2005. Characterization and expression of the chicken proglucagon and corresponding receptor genes. BARC Poster Day. Interpretive Summary:
Technical Abstract: In mammals the proglucagon (PG) gene produces a single mRNA transcript that encodes glucagon and two glucagon-like peptide hormones (GLP-1 and GLP-2). These peptide hormones bind to specific receptors that are expressed in different tissues. The function of these hormones, in conjunction with their receptors, is to regulate various aspects of carbohydrate, lipid, and amino acid metabolism. The GLPs also affect pancreatic insulin secretion, gastrointestinal (GI) growth and function, and feed intake. Our objectives were to characterize the structure and expression of the chicken PG gene and its corresponding receptor genes. The chicken PG gene has been sequenced and the mechanisms for producing multiple transcripts have been determined. Two distinct classes of PG mRNA were found and have been designated as class A and class B. We conclude that the two classes of mRNA result from alternative splicing of the chicken PG gene transcripts producing unique 3’ and 5’ ends. These mRNAs were co-expressed in pancreas, proventriculus, duodenum, brain, liver, breast muscle, heart, abdominal fat, lung, kidney, and spleen. The two classes share common sequence including the portion of the coding region (CDS) that contains glucagon and GLP-1. Class A has a smaller CDS and lacks the portion of the CDS that includes GLP-2, however, class B has an extended CDS which includes GLP-2. Both mRNAs have distinct 3’ untranslated regions that differ in size and sequence. Present within each class of PG mRNA are two variant forms arising from the incorporation of an alternate first exon. Gene specific RT-PCR assays were developed to determine individual mRNA levels in different tissues relative to an 18S rRNA internal standard. Pancreas and proventriculus displayed the highest expression levels of class A and class B mRNA. We have also identified glucagon, GLP-1, and GLP-2 receptor gene transcripts. Glucagon receptor was highly expressed in liver and abdominal fat but was low in pancreas. GLP-2 receptor gene expression was highest in pancreas, brain, and GI tract. Expression of GLP-1 receptor was high in all tissues studied except for liver, heart, and breast muscle. Plasma glucagon and GLP-1 levels were found to increase in response to starvation and decreased after subsequent re-feeding. However, starvation with subsequent re-feeding did not have a significant effect on PG gene expression in pancreas, proventriculus, duodenum, and brain. The expression level of glucagon, GLP-1, and GLP-2 receptor genes in specific tissues may indicate sites of action for the proglucagon peptide hormones.