Renal kallikrein mRNA localization by in situ hybridization

Tissue kallikrein gene expression in rat kidney was examined by in situ hybridization histochemistry. A rat tissue kallikrein cDNA probe, 534 bases in length and complementary to the 3' end of kallikrein mRNA was first used in Northern blot analysis to demonstrate the existence of tissue kallikrein mRNA in rat kidney. Then, kallikrein mRNA's localization in rat kidney sections was studied in situ hybridization histochemistry using the same probe. Positive signals were concentrated in the renal cortex at the vascular pole of the glomeruli and to a lesser degree, the distal tubular cells. Prehybridization with the unlabeled probe can abolish the positive signal; the same result can also be achieved by pretreatment of the tissue section with ribonuclease. By using the same technique, tissue kallikrein mRNA was also localized in granular convoluted tubule and striated duct cells of rat submandibular gland. The results suggest a new site of renal kallikrein synthesis at the vascular pole of the glomerulus. These findings, coupled with the previous studies that tissue kallikrein can participate in activation and releasing of renin, raise a potential physiological role of kallikrein in renin release or prorenin processing at juxtaglomerular cells.