Structure of the murine Pit1 phosphate transporter/retrovirus receptor gene and functional characterization of its promoter region

Abstract

The Pit1 phosphate transporter (formerly also called Glvr-1) probably plays an important role in regulated phosphate handling in bone-forming cells. In this study, we describe the structure of the mouse Pit1 gene, as well as some functional characteristics of its promoter region in murine bone cells. Screening of a genomic library led to the isolation of two overlapping lambda clones containing 7kb of 5' flanking region, as well as the 10 exons of the mouse Pit1 gene corresponding to the published cDNA. The translation start site is located within exon I and the stop codon within exon X. The overall structure of the mouse gene is very similar to that of its human homolog, except for the presence of an additional 5' untranslated exon in human. The structure of the 5' untranslated region of the mouse gene was thus further investigated using rapid amplification of cDNA ends in murine ATDC5, MC3T3-E1 and Swiss 3T3 cells. The results indicate that, compared to the published cDNA, the mouse Pit1 gene contains in fact one additional 5' exon, which we named exon IA. Reporter gene assays demonstrate the presence of a functional TATA box containing promoter upstream of exon IA. This description of the murine Pit1 gene and of its promoter region paves the way to more detailed analyses concerning the regulation of Pit1 transcription in mouse cells. Furthermore, a comparison of mouse and human promoters will hopefully allow a better understanding of general mechanisms regulating Pit1 expression in different species.