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J. Cell Biol.,
Volume 144, Number 5, March 8, 1999 857-868




* Medical Research Council Group in Molecular Biology of Membranes, *Department of Biochemistry and § Department of
Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada TGG 2H7; Calreticulin is a ubiquitous Ca2+ binding protein, located in the endoplasmic reticulum lumen,
which has been implicated in many diverse functions including: regulation of intracellular Ca2+ homeostasis,
chaperone activity, steroid-mediated gene regulation, and cell adhesion. To understand the physiological
function of calreticulin we used gene targeting to create
a knockout mouse for calreticulin. Mice homozygous
for the calreticulin gene disruption developed omphalocele (failure of absorption of the umbilical hernia)
and showed a marked decrease in ventricular wall
thickness and deep intertrabecular recesses in the ventricular walls. Transgenic mice expressing a green fluorescent protein reporter gene under the control of the
calreticulin promoter were used to show that the calreticulin gene is highly activated in the cardiovascular system during the early stages of cardiac development.
Calreticulin protein is also highly expressed in the developing heart, but it is only a minor component of the
mature heart. Bradykinin-induced Ca2+ release by the
InsP3-dependent pathway was inhibited in crt
Banting and Best
Department of Medical Research,
Department of Anatomy and Cell Biology, University of Toronto, Toronto, Canada M5S 1A8;
and ¶ Department of Geriatrics, Geneva University Hospitals, Geneva, Switzerland 1211 Geneve
/
cells,
suggesting that calreticulin plays a role in Ca2+ homeostasis. Calreticulin-deficient cells also exhibited impaired nuclear import of nuclear factor of activated T
cell (NF-AT3) transcription factor indicating that calreticulin plays a role in cardiac development as a component of the Ca2+/calcineurin/NF-AT/GATA-4 transcription pathway.
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