Tissue-specific and hormonal regulation of calbindin-D9K fusion genes in transgenic mice.

The rat Calbindin-D9K (CaBP9K) gene is mainly expressed in intestine, uterus, and lung and is regulated in a complex tissue-specific manner. To analyze the role of potential regulatory elements, previously defined by DNaseI hypersensivity, we made transgenic mice containing truncated rat CaBP9K fusion gene with simian virus 40 large T antigen and the chloramphenicol acetyltransferase as reporter genes. The transgenes contained CaBP9K promoter fragments with 5' end points at -4400, -1011, and -117 base pairs (bp), whereas the 3' end points was at +365 bp. Northern blot analysis of T antigen expression and chloramphenicol acetyltransferase enzyme-linked immunosorbent assay indicated that a positive element, probably the distal intestine-specific DNaseI HS, necessary to target the expression of the transgene in the intestine, is present between -4400 and -1011 bp. The cephalo-caudal gradient of expression of the transgene along the small intestine was similar to those of the endogenous gene, but an ectopic expression of the transgene was observed in the colon. The -1011 transgene was expressed in epithelial alveolar cells of the lung, in renal proximal tubule cells, and in uterine myometrium, as judged from immunocytochemical, histological, and Northern blot analyses. The shortest, -117 construct was only expressed in uterine myometrium, and it was under a strict estrogen dependence like the endogenous gene. Finally, responsiveness to vitamin D in the duodenum was observed with the largest, -4400 construct. Thus, different tissues utilize distinct cis-acting elements to direct and regulate the expression of the rat CaBP9K gene.