RT-PCR microlocalization of mRNAs for calbindin D_28k and vitamin D receptor in the murine nephron

-The spa-tial relationship between vitamin D receptor (VDR) and calbindin D_28k [calcium binding protein D_28k (CaBP-D_28k)] gene expression within the murine kidney was studied by localizing their mRNAs in discrete nephron structures using reverse transcription-polymerase chain reaction (RT-PCR). Primers for β-actin mRNA were used as a control for the presence of tissue during RT-PCR for CaBP-D_28k mRNA. mRNA for CaBP-D_28k was found only in distal convoluted tubules (DCTs), connecting tubules (CNTs), and cortical collecting ducts (CCDs). In contrast, VDR mRNA was detected in glomeruli, S2 proximal convoluted tubules, cortical thick ascending limbs of Henle's loop, DCTs, CNTs, and initial CCDs. The presence of both VDR and CaBP-D_28k mRNA in DCTs, CNTs, and CCDs is consistent with the hypothesis that calcitriol acts via the VDR to stimulate CaBP-D_28k synthesis. Conversely, the presence of VDR mRNA in other parts of the nephron suggests that calcitriol has genomically mediated actions within the kidney in addition to stimulation of CaBP-D_28k synthesis.