DEVELOPMENTAL EXPRESSION OF 2 MEMBERS OF A NEW CLASS OF TRANSCRIPTIONFACTORS .1. EXPRESSION OF ARYL-HYDROCARBON RECEPTOR IN THE C57BL 6N MOUSE EMBRYO/

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcriptio n factor with a basic region/helix-loop-helix (bHLH) motif. AhR has be en sequenced and the functional domains defined and there is informati on on the formation of complexes with other peptides and interactions with DNA, although these areas continue to be investigated, AhR mediat es many biological effects such as developmental toxicity, including i nduction of cleft palate and hydronephrosis, This regulatory protein i s expressed in embryonic liver and has been immunohistochemically loca lized in cells of human and mouse secondary palate. The expression of AhR in embryonic tissues and its ability to disrupt development sugges ts a significant role for this protein in development, The present stu dy examines the pattern of AhR expression in the C57BL/6N mouse embryo from gestation days (GD) 10-16, using in situ hybridization and immun ohistochemical analysis. AhR mRNA was localized with S-35-RNA antisens e riboprobe (cAh1 probe, 1.8 Kb amino terminal DNA), AhR protein was l ocalized with purified monoclonal antibody (RPT-9) raised against the N-terminal peptide sequence. AhR mRNA and protein were expressed in GD 10-13 neuroepithelium, and as development progressed the levels in br ain decreased. GD 10-12 embryos also showed AhR in branchial arches, h eart, somites, and liver, AhR protein and mRNA in heart were highest a t GD 10-11 and decreased with age. In liver, AhR mRNA and protein leve ls increased and nuclear localization became more pronounced with gest ational age. In GD 14-16 embryos levels in liver and adrenal were high est, but AhR was present in ectoderm, bone, and muscle. AhR expression was specific for both cell type, organ/tissue, and developmental stag e, suggesting that this novel ligand-activated transcriptional regulat or may be important in normal embryonic development. (C) 1995 Wiley-Li ss, Inc.