Expression and Localization of General Transcription Factor IIA Gene in Hypokalemic Rat

Lee, Chang Bae; Lee, Yong Chan; Cho, Hye Jung; Lee, Song Eun; Bae, Choon Sang; Kim, Baik Yoon; Park, Sung Sik; Ahn, Kyu Youn

Abstract

Potassium balance in chronic hypokalemia is regulated by ion channels, ion transporters, and various related genes. We isolated general transcription factor IIA (GTF IIA) gene using a DNA chip microassay, a useful method in cloning genes. Northern analysis and in situ hybridization (ISH) were carried out to analyze the expression and localization of GTF IIA mRNA in rat in relation to the amount of potassium in the diet. Isoform-specific 32P-labeled cDNA (Northern analysis) or digoxigenin-labeled cRNA (ISH) probes were used. Northern analysis demonstrated that GTF IIA mRNA was expressed abundantly in testis; modestly in heart, kidney, lung, adrenal gland, liver, and spleen; and weakly in brain, distal colon, duodenum, salivary gland, and stomach. In potassium-restricted animals, GTF IIA expression was decreased in the kidney, adrenal gland, and spleen, but expression was restored to normal levels in L3w. The expression level in the lung was decreased in L3d and L2w, and increased in L1w and L3w. ISH showed that mRNA for the GTF IIA gene was detected in the distal convoluted tubule, S3 segment of the proximal tubule, and cortical collecting duct in the normal group. In potassium-restricted groups, the hybridization signal was detected in the distal convoluted tubule, S3 segment of the proximal tubule, and entire collecting tubule. The signal intensity of the outer and inner medullary collecting ducts was higher in the potassium-restricted group than in the normal group but was decreased in the distal convoluted tubule and S3 segment of the proximal tubule. In the normal group, mRNA of the GTF IIA gene was detected in the zona glomerulosa cells of the adrenal gland, lymphocytes of the marginal zone, germinal center of the spleen, and bronchial epithelium and lymphocytes of the lung. mRNA for the GTF IIA gene was also detected in the cells of the basal portion of the intestinal glands of the distal colon and stomach, and in spermatogonia and spermatocytes of the seminiferous tubule. These results suggest that expression of GTF IIA differs between various tissues and that increased expression of the GTF IIA gene in the outer and inner medullary collecting ducts of the hypokalemic kidney might regulate the ion transporter genes in these segments.