A murine transgenic model for transcriptional regulation of the Na/Pi-IIa major renal phosphate cotransporter

Levels of the type IIa Na/P_i (Na/Pi-IIa) cotransporter, which serves as the principal mediator of phosphate reabsorption in the kidney, can be modulated through posttranscriptional or posttranslational mechanisms by dietary, hormonal, and pharmacological influences. Previous studies have not demonstrated clear-cut evidence for modulation of Na/Pi-IIa cotransporter levels through transcriptional mechanisms. We have previously demonstrated that a 4.7-kb rat genomic fragment upstream of the rodent Npt2 gene encoding the Na/Pi-IIa cotransporter, is sufficient to mediate its transcriptional activity in vitro (Shachaf C, Skorecki KL, Tzukerman M. Am J Physiol Renal Physiol 278: F406-F416, 2000). Accordingly, we have established an in vivo experimental model in which this Npt2 genomic fragment fused upstream of a Lac Z reporter gene was expressed as a transgene in mice. The nine independent transgenic founder lines generated exhibited Lac Z reporter gene expression specifically in the renal cortex. This renal cortical-specific expression driven by the Npt2 promoter was confirmed at the mRNA and protein levels using RT-PCR, histochemistry, and Lac Z enzymatic activity. Furthermore, the expression of the transgene correlated with expression of the endogenous Npt2 gene during embryonic and early postnatal development. Thus we have generated a transgenic mouse model which will enable in vivo investigation of the contribution of transcriptional mechanisms to the overall regulation of Na/Pi-IIa expression under physiological and pathophysiological conditions.