Striking Evolutionary Conservation of a cis-Element Related to Nuclear Receptor Target Sites and Present in TR2 Orphan Receptor Genes

A systematic scanning of nucleic acid databases for DNA elements made of combinations of RGGTCA nuclear receptor half sites, has revealed that identical 19 nucleotide-long motifs composed of two inverted RGGTCA sites with a spacing of 7 nucleotides (IR7), are present upstream of the regions coding for the human TR2 and of the sea urchin SpSHR2 orphan receptors. We have developed an experimental strategy based on PCR, to check if this IR7 could correspond to an unusually long cis-element, conserved along evolution and regulating the TR2 genes. We found that indeed IR7 is present in the 5′ untranslated region of TR2 genes from all species tested, includingXenopus,rainbow trout, zebrafish and mouse. The exact conservation throughout the animal kingdom of such a long, non repetitive and non coding genomic region, highly suggests that it should ensure important biological functions. In addition, this work has allowed the identification of a new, non coding, upstream exon in the mouse TR2 gene present in testicular TR2 mRNAs.