Estrogen and a calcium flux dependent factor modulate the calbindin gene expression in the uterus of laying hens

The dependency of calbindin 28K synthesis on estrogen and vitamin D and its relationship with calcium transfer were investigated in the uterus of laying hens by dot blot hybridization analysis using as a probe a cDNA coding for calbindin. Estrogen stimulated growth of the oviduct and uterine calbindin systhesis in juvenile D-deficient female chicks. In laying hens, calbindin mRNA increased most markedly during shell deposition but calbindin concentrations did not fluctuate during the ovulatory cycle. Suppression of shell formation within a few hours reduced calbindin mRNA levels and lowered uterine calbindin concentrations when egg expulsions were continued for several days. The concentration of calbindin and its mRNA increased when shell formation resumed in hens previously laying shell-less eggs. These increases were maintained in hens parathyroidectomized just before shell resumption. Lowering dietary calcium decreased uterine calcium transfer and calbindin concentration but its mRNA level was unaffected. It is suggested that uterine calbindin synthesis is regulated in a tissue-specific manner through transcriptional mechanisms irrespective of change in vitamin D; calbindin synthesis is stimulated by estrogens as part of its effect on oviductal growth but its regulation predominently involves a calcium flux dependent factor associated with shell calcification.