Calbindin D(9k) knockout mice are indistinguishable from wild-type mice in phenotype and serum calcium level.

Since the discovery of calbindin D(9k), its role in intestinal calcium absorption has remained unsettled. Further, a wide distribution of calbindin D(9k) among tissues has argued for its biological importance. We discovered a frameshift deletion in the calbindin D(9k) gene in an ES cell line, E14.

CYP27B1 null mice with LacZreporter gene display no 25-hydroxyvitamin D3-1alpha-hydroxylase promoter activity in the skin.

The hormonally active form of vitamin D(3),1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is synthesized in the kidney through a tightly regulated reaction catalyzed by 25-hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase), the product of the CYP27B1 gene. Through gene targeting in embryonic stem cells, we engineered a mouse strain in which the coding region of the 1alpha-hydroxylase gene is replaced by the genes for beta-galactosidase (lacZ) and neomycin resistance. Null mice produced no detectable 1alpha-hydroxylase transcript.