Molecular cloning and expression of chicken carbohydrate response element binding protein and Max-like protein X gene homologues.

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 Western blotting, 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.