Submitted to: Molecular and Cellular Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/25/2008
Publication Date: 5/1/2008
Citation: Proszkowiec-Weglarz, M., Humphrey, B.D., Richards, M.P. 2006. Molecular cloning and expression of the chicken carbohydrate response element binding protein and Max-like protein X gene homologues. Molecular and Cellular Biochemistry. 312(1-2):167-184.
Interpretive Summary: Commercial strains of broiler chickens which have been intensively selected for rapid growth and increased meat yield do not adequately regulate their voluntary food intake to achieve energy balance. Instead, these birds are prone to overeating and excessive fattening (obesity). It is therefore important to better understand the mechanisms governing carbohydrate and lipid metabolism in these birds so that new strategies for feeding and management of commercial broiler flocks can be developed. In mammals, carbohydrate response element binding protein (ChREBP), a transcription factor that “senses” glucose levels, is a key regulator of carbohydrate and lipid metabolism. In response to elevated glucose levels resulting from increased food intake, ChREBP is activated and promotes an increase in the expression of genes involved in fatty acid biosynthesis from excess glucose. Since there has been no prior investigation of ChREBP in birds, we decided to identify and characterize the genes that code for ChREBP and its co-activator protein, Max-like protein X (Mlx) in broiler chickens. This is the first report to investigate ChREBP and Mlx expression in different avian tissues. Additionally, we were able to detect the presence of ChREBP protein in liver tissue. We also studied the expression of several other genes that work in concert with ChREBP to regulate of lipid synthesis. Together, our findings establish, for the first time, that genes for ChREBP and its co-activator Mlx are present and active in chickens. This work provides new information to researchers interested in studying the molecular basis for the glucose-dependent regulation of lipid metabolism in avian species. We conclude that ChREBP most likely plays a key role in the regulation of energy balance in broiler chickens much like it does in mammals.
Technical Abstract: Carbohydrate response element binding protein (ChREBP) and sterol regulatory element binding protein-1c (SREBP-1c) are transcription factors that are known to be key regulators of glucose metabolism and lipid synthesis in mammals. Since ChREBP and its co-activator Max-like protein X (Mlx) have not been identified in birds, the objectives of this work were to clone, sequence and characterize the genomic organization of ChREBP and Mlx genes and to determine the expression of ChREBP, Mlx and several related genes including liver X receptor (LXR), SREBP-1 and thyroid hormone responsive spot 14 (Spot 14) in chickens. Alternative splicing resulted in two ChREBP mRNA transcript variants that code for predicted proteins of 895 and 869 amino acids. The chicken Mlx gene produced a single mRNA transcript that codes for a predicted protein of 245 amino acids. Chicken ChREBP and Mlx predicted proteins shared high amino acid homology with select portions of corresponding mammalian proteins. In chickens, Mlx, SREBP-1 and LXR were expressed at comparable levels in all tissues examined. However, ChREBP demonstrated significant tissue-specific expression with the highest mRNA levels found in liver and duodenum and Spot 14 was expressed predominantly in liver and abdominal fat. Using immunoassay, the presence of ChREBP protein was detected in chicken liver tissue. Our findings add new insight into a potential role for specific transcription factors such as ChREBP and Mlx in the glucose-dependent regulation of lipogenesis in birds.