Human Reproduction, Vol. 17, No. 11, 2938-2947,
November 2002
© 2002 European Society of Human Reproduction and Embryology
Calcium-binding proteins and calcium-release channels in human maturing oocytes, pronuclear zygotes and early preimplantation embryos
1 CReATe (Canadian Reproductive Assisted Technology) Program Inc., Toronto, Ontario, Canada, 2 Department of Anatomy and Cell Biology, University of Toronto, 3 Department of Obstetrics and Gynecology, Sunnybrook and Women’s College Health Sciences Center, University of Toronto and 4 Canadian Institutes of Health Research Group in Molecular Biology of Membrane Proteins and the Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada
BACKGROUND: The study aim was to investigate the presence and localization of Ca2+-binding proteins and Ca2+-release receptor channels in human maturing oocytes, pronuclear zygotes and preimplantation embryos. METHODS: Immunocytochemical analysis, using specific antibodies against the proteins being studied, followed with confocal laser microscopy, was performed on human oocytes and embryos. RESULTS: Calreticulin and calsequestrin (the two major calcium storage proteins of somatic cells), two types of calcium release receptors, the inositol trisphosphate and ryanodine receptors (InsP3R-2, RyRs-1,2,3), and the molecular chaperone, calnexin, were identified in all investigated cell types. Calreticulin was predominant in the cell cortex and in the nuclear envelope, while calsequestrin was distributed throughout the entire cytoplasm. Generally, localization of the InsP3R-2 and RyRs was similar to that of calreticulin and calsequestrin respectively. Both types of receptor were enriched in the subplasmalemmal region of meiotic oocytes. In addition, the InsP3R was detected in the nuclear structures of oocytes and blastomeres. Calnexin distribution overlapped with that of calreticulin but appeared to be present in distinct subcompartments. CONCLUSIONS: Human oocytes and embryos express the calcium sequestration and release proteins in highly organized and developmentally regulated patterns. Fine-tuning of these proteins may play a crucial role in regulation of Ca2+ transience during oocyte maturation, fertilization and early embryo development.
Key words: calcium release receptors/calnexin/calreticulin/calsequestrin/human embryos
5 To whom correspondence should be addressed at: CReATe Program Inc., 790 Bay Street, Suite 1020, Toronto, Ontario M5G 1N8, Canada. E-mail: hbalakier{at}sympatico.ca
The results of this study were presented at the 57th Annual Meeting of the American Society for Reproductive Medicine, Orlando, Florida, USA, October 20–25, 2001
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