Introduction: 

Renal handling of inorganic phosphate (P_i) is mediated by two members of the SLC34 family of solute carriers: SLC34A1/NaPi-IIa and SLC34A3/NaPi-IIc. NaPi-IIc, a protein of about 600 residues, was long considered a juvenile cotransporter, with little or no contribution to P_i homeostasis in the adult kidney. However, recent findings associating this cotransporter with hypophosphatemic syndromes in humans call for a reevaluation of its functional implications.

Methodology: 

Here we describe the generation of a mouse model in which NaPi-IIc can be knocked down in an inducible manner. A targeting vector was first engineered by introducing loxP sites in introns 4 and 13. The loxP-flanked sequence encodes residues 61 to 440 of the transporter. Following conditional targeting of the NaPi-IIc gene locus, we obtained mice harboring both alleles flanked by loxP sites (NaPi-IIc^fl/fl). NaPi-IIc^fl/fl were bred with Pax8rtTA/LC1 mice in which the renal expression of Cre recombinase can be induced by doxycycline. Further mating resulted in homozygous (NaPi-IIc^fl/fl) and heterozygous mutants (NaPi-IIc^fl/+) as well as wild type (NaPi-IIc^+/+) mice that also coexpressed Pax8 and Cre.

Results: 

Administration of doxycycline (2 mg/ml in 2% sucrose) for 10 days to 4 weeks old animals resulted in full ablation of the expression of NaPi-IIc mRNA (and strong reduction of the protein) in NaPi-IIc^fl/fl mice, about 50% mRNA reduction in NaPi-IIc^+/fl animals, without changes in NaPi-IIc^+/+ mice.

Conclusion: 

We can successfully induce the knockout of NaPi-IIc, a maneuver that will allow us to study its relative contribution in young and adult mice.