Molecular characterization and developmental expression of the aryl hydrocarbon receptor from the chick embryo

The aryl hydrocarbon receptor (AhR) was cloned from the chick embryo and it s function and developmental expression characterized. Chicken AhR cDNA cod ed for 858 amino acid protein and 396 bp of 3' UTR. The basic helix-loop-he lix domain exhibited 87-100% amino acid identity to avian, mammalian, and a mphibian AhR, and 69-74% to piscine AhR. The PAS (Per-ARNT-Sim) region was slightly less well conserved with (a) 97% identity to other avian sequences , (b) 81-86% to amphibian and mammalian AhR, and (c) 64-69% with piscine Ah R. The carboxy terminus diverged the most among species with less than 53% amino acid identity between chicken and any available mammalian and piscine AhR sequences. The chicken AhR mRNA and protein were 6.1 kb and 103 kDa, r espectively. Chicken AhR dimerzed with human AhR nuclear translocator and b ound the mammalian dioxin-response element in a ligand-dependent manner. Ah R protein was detected in neural ganglia; smooth, cardiac, and skeletal mus cle; and epithelium involved in epithelial-to-mesenchymal transformations, such as pituitary, gastrointestinal tract, limb apical-ectodermal ridge, an d kidney collecting ducts. AhR mRNA was detected in all tissues expressing protein, except myocardium. Cytochrome P4501A4 mRNA was highly induced by 2 ,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a subset of tissues expressing AhR, including small intestine, liver, kidney, blood vessels, and outflow tract myocardium. In conclusion, the AhR sequence and function is highly co nserved between birds and mammals, and although many tissues express AhR du ring chick embryo development, only a subset are responsive to TCDD inducti on of CYP1A4. (C) 2000 Elsevier Science Inc. All rights reserved.