Analysis of rat vitamin D-dependent calbindin-D(28k) gene expression

We report the use of a cloned cDNA for mammalian calbindin-D(28k) (28-kDa vitamin D-dependent calcium-binding protein) to study the expression of the rat calbindin gene. Tissue distribution studies, using Northern analysis, indicated that calbindin-D-(28k)-mRNA is detected in rat kidney and brain but is not detected in rat intestine, testes, bone, pancreas, liver, lung, or skeletal muscle. Both rat kidney and brain contain three RNA species (1.9, 2.8, and 3.2 kilobase pairs). The regulation of the gene was characterized by both Northern and slot blot analysis. Hormonal regulation, developmental expression of calbindin-D(28k)-mRNA, and the effect of dietary alteration were examined. In the kidney all three species of mRNA were dependent on the presence of 1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) for their induction. The time course of induction of renal calbindin-D(28k)-mRNA indicated that a significant increase in calbindin-D-mRNA was detectable as early as 2 h following a single injection of 1,25-(OH)₂D₃ (200 ng/100 g of body weight), reaching a maximum at 12 h. Unlike the kidney high levels of calbindin-D(28k)-mRNA were observed in the brain of vitamin D-deficient rats. The concentration of calbindin-D(28k)-mRNA in brain was unchanged after 1,25-(OH)₂D₃ administration. Developmental studies indicated that calbindin-D-mRNA in rat kidney and brain is present prior to birth but is developmentally regulated in a tissue-specific manner. The most pronounced changes in the abundance of renal calbindin-D(28k)-mRNA occur between birth and 1 week of age. Unlike the kidney a large increase in brain calbindin-D(28k)-mRNA occurs at a larger time, between 1 and 2 weeks of age (the period of major synapse formation). In dietary alteration studies results of Northern blot analysis indicate that low dietary phosphorus results in increased calbindin-D-mRNA in kidney but not in brain. These studies represent the first analysis of the rat calbindin-D(28k) gene and its regulation in vivo. Our findings suggest that in rat kidney and brain there are significant differences both in the expression of the gene for calbindin-D(28k) and its regulation by 1,25-(OH)₂D₃.