The co-localization of stanniocalcin protein, mRNA and kidney cell markers in the rat kidney

Stanniocalcin (STC) is a glycoprotein hormone that was first discovered in fish and recently identified in mammals. STC immunoreactive (STCir) cells have been identified in rat kidney and there is also evidence that the hormone functions as a regulator of renal phosphate homeostasis. In the present study we have identified STCir cells and tubules in the rat kidney by correlative immunocytochemistry using antibodies to STC and specific antigenic markers (Tamm-Horsfall protein and anion exchanger-1). The cellular sites of STC gene expression were also identified by in situ hybridization. Correlative immunocytochemistry revealed that STCir was present in all proximal straight tubule cells, all cortical thick ascending limb cells, all distal convoluted tubule cells, and both principal and α-intercalated cells of the collecting duct system. On the other hand, in situ hybridization revealed that the STC gene was expressed only in cortical and medullary collecting duct cells. This suggests either that STC is being sequestered by segments that do not express the gene (making them putative targets of the hormone), or that STC mRNA levels were simply too low in these other segments to be detected by in situ hybridization.