A,B) Time-course expression of A) Cyp27b1 and B) Cyp24A in the kidney of WT and Col4a3−/− mice. Both Cyp27b1 and Cyp24a1 message expression were age-dependently increased in Col4a3−/− mice compared to wild-type controls. C, D) Expression of C) Cyp27b1 and D) Cyp24A in the kidney of 12 week-old WT, Col4a3−/− Fgf23−/− and compound Fgf23−/− ol4a3−/− mice. N≥4, p<0.05, * vs. WT, a vs. Col4a3−/−. mRNA expression normalized by GAPDH and relative to values in wild-type controls. E) Relationship between serum FGF23 and 24,25(OH)2D levels. There was a significant inverse correlation between serum FGF23 and serum 24,25(OH)2D levels. (circles, wild-type, triangles, Col4a3−/− mice) F) Expression of Cyp2R1 and cyp27A1 in the liver. mRNA expression normalized by GAPDH and relative to values in wild-type controls. There was no significant difference in expression of the enzymes that generate 25(OH)D in Col4a3−/− mice compared to wild-type mice.