The genomic organisation, sequence and functional analysis of the 5′flanking region of the chicken estrogen receptor gene

The cDNA of many members of the nuclear receptor superfamily has been cloned. Recently more effort has been expended on the analysis of these genes at the genomic level and on the factors controlling their expression. The genomic organization of the chicken estrogen receptor gene is presented and compared to the other members of the superfamily of hormone receptor genes with emphasis on the relationship to the functional domains. The results show that the gene is divided into eight exons and that the position of the intron/exon boundaries are as in the human gene but different to the trout estrogen receptor gene. Primer extension and cDNA clone isolation was used to determine the transcription start site and 3.0 kb of 5′ flanking sequence was generated. There is striking sequence homology to the human estrogen receptor promoter and there is a well positioned "typical" TATA sequence, with potential candidate CAAT box sequences close to the start site of transcription. In transient transfection assays, subfragments of this region drove CAT expression in chicken embryo fibroblasts, and the level was increased further with the addition of forskolin, but not phorbal myristate acetate. Including sequences more distal to the cap site in promoter constructs, completely abolished the promoter activity and forskolin inducibility, indicating the presence of strong silencing activity.