Cardiac-specific expression of calcineurin reverses embryonic lethality in calreticulin-deficient mouse

Calreticulin is an endoplasmic reticulum resident Ca²⁺-binding chaperone. The importance of the protein is illustrated by embryonic lethality because of impaired cardiac development in calreticulin-deficient mice. The molecular details underlying this phenotype are not understood. In this study, we show that overexpression of activated calcineurin reverses the defect in cardiac development observed in calreticulin-deficient mice and rescues them from embryonic lethality. The surviving mice show no defect in cardiac development but exhibited growth retardation, hypoglycemia, increased levels of serum triacylglycerols, and cholesterol. Reversal of embryonic lethality because of calreticulin deficiency by activated calcineurin underscores the impact of the calreticulin-calcineurin functions on the Ca²⁺-dependent signaling cascade during early cardiac development. These findings show that calreticulin and calcineurin play fundamental roles in Ca²⁺-dependent pathways essential for normal cardiac development and explain the molecular basis for the rescue of calreticulin-deficient phenotype.