TISSUE-SPECIFIC AND HORMONAL-REGULATION OF CALBINDIN-D9K FUSION GENESIN 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 defi ned by DNaseI hypersensivity, we made transgenic mice containing trunc ated rat CaBP9K fusion gene with simian virus 40 large T antigen and t he chloramphenicol acetyltransferase as reporter genes. The transgenes contained CaBP9K promoter fragments with 5' end points at -4400, -101 1, and -117 base pairs (bp), whereas the 3' end points was at +365 bp. Northern blot analysis of T antigen expression and chloramphenicol ac etyltransferase enzyme-linked immunosorbent assay indicated that a pos itive element, probably the distal intestine-specific DNaseI HS, neces sary to target the expression of the transgene in the intestine, is pr esent between -4400 and -1011 bp. The cephalo-caudal gradient of expre ssion 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 epithelia l alveolar cells of the lung, in renal proximal tubule cells, and in u terine myometrium, as judged from immunocytochemical, histological, an d Northern blot analyses. The shortest, -117 construct was only expres sed in uterine myometrium, and it was under a strict estrogen dependen ce like the endogenous gene. Finally,res ness to vitamin D in the duod enum was observed with the largest, -4400 construct, Thus, different t issues utilize distinct cis-acting elements to direct and regulate the expression of the rat CaBP9K gene.