Calbindin-D9K (CaBP9K) Gene: A Model for Studying the Genomic Actions of Cacitriol and Calcium in Mammals
The 9KDa vitamin D-dependent calcium-binding protein (CaBP9K) now termed calbindin-D9K (1), is characteristic of the rat and other mammals and was discovered by Wasserman’s group in 1967 (2). This acidic protein has 2 calcium-binding sites organized as “EF-hands” (3, 4). CaBP9K was first located in the absorptive cells of the duodenum but is also found in the epithelial cells of the placenta and uterus, as demonstrated by in situ hybridization (5, 6) using a specific cloned CaBP cDNA (7). Northern analysis shows a single 0.5 kb long transcript from rat duodenum, fetal and maternal placenta and uterus (5, 6). CaBP9K gene expression in rat duodenum is hormonally controlled by 1,25(OH)2D3 (calcitriol), the active form of vitamin D. 1,25(OH)2D3 receptors have been identified and localized in the duodenum (8) and duodenal concentration of CaBP9K is dependent upon the vitamin D status (9).
KeywordsAbsorptive Cell CaBP9K mRNA Maternal Placenta Duodenal Concentration Protein Messenger Ribonucleic Acid
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