EXPRESSION OF ARNT, ARNT2, HIF1-ALPHA, HIF2-ALPHA AND AH RECEPTOR MESSENGER-RNAS IN THE DEVELOPING MOUSE

The basic helix-loop-helix-PAS (bHLH-PAS) protein ARNT is a dimeric pa rtner of the Ah receptor (AHR) and hypoxia inducible factor 1 alpha (H IF1 alpha). These dimers mediate biological responses to xenobiotic ex posure and low oxygen tension. The recent cloning of ARNT and HIF1 hom ologues (ARNT2 and HIF2 alpha) indicates that at least six distinct bH LH-PAS heterodimeric combinations can occur in response to a number of environmental stimuli. In an effort to understand the biological rele vance of this combinatorial complexity, we characterized their relativ e expression at a number of developmental time points by parallel in s itu hybridization of adjacent tissue sections. Our results reveal that in general there is limited redundancy in the expression of these six transcription factors and that each of these bHLH-PAS members display s a unique pattern of developmental expression emerging as early as em bryonic day 9.5. (C) 1998 Elsevier Science Ireland Ltd.