Michal Opas

Department of Laboratory Medicine & Pathobiology


UofT campus: Medical Sciences Building (MSB)
1 Kings College Circle, Room 6326, Toronto, Ontario Canada M5S 1A8
Research Interests
Cardiovascular, Molecular & Cell Biology
Appointment Status

Dr Opas obtained his M.Sc. in 1973 in Cell Biology at the Warsaw University, Warsaw, Poland and Ph.D in 1977 in Cell Biology, from Polish Academy of Sciences, Warsaw, Poland.

In 1981 he came to Toronto as a Postdoctoral Fellow of the Muscular Dystrophy of Canada.

He presently is a Professor with the Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, cross appointed to the Institute of Medical Science, Temerty Faculty of Medicine, University of Toronto.

He also is a Member of the Heart and Stroke / Richard Lewar Centre of Excellence in Cardiovascular Research, University of Toronto.


Research Synopsis


Cell commitment and differentiation are governed by many factors, some of them extrinsic (e.g., matrix mechanics), others intrinsic (e.g., tissue-specific transcription factors and signalling pathways), many of which depend on calcium-binding proteins.

One such protein is calreticulin, the cell biology of which has been the subject of research in the Opas laboratory for some time. Calreticulin is a ubiquitous calcium-binding chaperone of the ER/SR, which affects calcium homeostasis and gene expression, particularly that of steroid-sensitive and adhesion-related genes.

Our interest is in the role of calreticulin in determining the output of ES cell differentiation.

Calreticulin, either by its role in intracellular calcium homeostasis or as a chaperone, modulates actions of tissue-specific transcription factors and signalling pathways that control cell lineage specification and expression of the differentiated phenotype.

The biomechanical properties of the growth substratum, by modulating cell adhesiveness, shape, and cytoarchitecture, influence the phenotype of many cells, including ES cells. Cell adhesion and shape are also modulated by calreticulin (as shown by Dr Marc Fadel who is my graduate). Thus, both cell shape and signalling pathways are affected by calreticulin expression level. Consequently, we postulate that the cell fate choice may be controlled by the combinatorial action of calreticulin level of expression and biomechanics of the cell's environment (niche).

Thus our research might be referred to as cytomechanics of differentiation.

We have been studying the role of calreticulin ES cell choice of fate.

We discovered that calreticulin acts as a switch either promoting (bone) or suppressing (fat) stem cell differentiation, while it seems to deregulate cardiogenesis.

Sometime ago we have proposed calreticulin to be a novel cardiac foetal gene involved in the calcineurin/GATA-4/NFATc pathway.

Calreticulin knockout causes embryonic lethality due to cardiac defects and calreticulin is transiently activated during heart development.

We (Dr Sylvia Papp, who is my graduate) have embarked on a project entailing cardiac differentiation from ES cells in which the calreticulin gene has been genetically manipulated. As heart-targeted overexpression of calreticulin also causes lethality due to cardiac defects, the protein seems to play a role not only in cardiomyogenesis but also in proper functioning of the differentiated cardiomyocyte.

Calreticulin is essential for cardiac development, however, nothing was known about its role in other ES cell lineages such as adipogenesis and skeletogenesis.

Given that calreticulin is crucial for both Ca homeostasis and ”quality control” during protein synthesis, we set out to elucidate the role for calreticulin and to examine its mechanistic effect on adipogenesis.

We showed, for the first time, a novel role for calreticulin as an inhibitor of cell commitment to adipogenesis. We have shown that this is effected via calreticulin’s calcium homeostasis function.

We also showed that the mechanism for calreticulin's effects resides in the indirect regulation of the calcineurin and CaMKII pathways, which are crucial for adipogenesis.

Our current work focuses on a role of calreticulin signalling in skeletogenesis, which often tends to be differentiation pathway alternative to adipogenesis.                                                             


Recent Publications


Selected publications

Embryonic Stem Cell work

Papp et al. 2009: Embryonic stem cell derived cardiomyogenesis: a novel role for calreticulin as a regulator. Stem Cells 27, 1507.

Szabo et al. 2009: Cell adhesion and spreading affect adipogenesis from ES cells: the role of calreticulin. Stem Cells. 27, 2092.

Karimzadeh, F. and M. Opas. 2017: Calreticulin Is Required for TGF-ß-Induced Epithelial-to-Mesenchymal Transition during Cardiogenesis in Mouse Embryonic Stem Cells. Stem Cell Reports 8, 1299.

Pilquil et al. 2020: Calreticulin regulates switch between osteoblast and chondrocyte lineages derived from murine embryonic stem cells. J. Biol. Chem. 295, 6861.

Alvandi et al. 2020: Calreticulin regulates Src kinase in osteogenic differentiation from embryonic stem cells. Stem Cell Res

Alvandi, Z. and M. Opas. 2020: c-Src kinase inhibits osteogenic differentiation in mESCs via enhancing Stat1 stability. PLoS ONE e0241646. 

Calreticulin, cytoskeleton, cell adhesion and motility

Opas et al., 1996: Calreticulin modulates cell adhesiveness via regulation of vinculin expression. J. Cell Biol. 135, 1913.,

Fadel et al. 1999: Calreticulin affects focal contact-dependent but not close contact-dependent cell-substratum adhesion. J. Biol. Chem. 274, 15085.,

Fadel et al., 2001: Calreticulin signals from the ER via β-catenin-associated pathways. J. Biol. Chem. 276, 27083.

Opas, M. and M.P. Fadel. 2007: Partial reversal of transformed fusiform phenotype by overexpression of calreticulin. Cell. Mol. Biol. Letters 12, 294.

Papp et al. 2007: Dissecting focal adhesions in cells differentially expressing calreticulin: a microscopical study. Biol. Cell. 99, 389.

Szabo et al. 2007: Differential calreticulin expression affects adhesion through calmodulin/CaM kinase II pathway. J. Cell. Physiol. 213, 269.,

Papp et al. 2007: Calreticulin affects fibronectin-based cell-substratum adhesion via the regulation of c-src activity. J. Biol. Chem. 282, 16585.

“Calreticulin, cytoskeleton, cell adhesion and motility” reviewed in Szabo et al. 2006: Calreticulin and cellular adhesion/migration-specific signalling pathways. J. Appl. Biomed., 4: 45. and Villagomez et al. 2009: Calreticulin and focal contact-dependent adhesion. Biochem. Cell Biol. 87, 545.

Calreticulin and cardiogenesis

Mesaeli et al., 1999: Calreticulin is essential for cardiac development. J. Cell Biol. 144, 857

Nakamura et al., 2001: Complete heart block and sudden death in mice over-expressing calreticulin. J. Clin. Invest. 107, 1245.

Guo et al. 2002: Cardiac specific expression of calcineurin reverses embryonic lethality in calreticulin-deficient mouse. J. Biol. Chem. 277, 50776.

Lozyk et al. 2006: Ultrastructural analysis of development of myocardium in calreticulin-deficient mice. BMC Developmental Biology 6, 54.

“Calreticulin and cardiogenesis” reviewed in Michalak, M. and M. Opas. 2009: Endoplasmic and sarcoplasmic reticulum in the heart. Trends Cell Biol. 19, 253.


Opas et al., 1991: Regulation of expression and intracellular distribution of calreticulin, a major calcium binding protein of non-muscle cells. J. Cell. Physiol. 149, 160.

Michalak et al. 1996: Endoplasmic reticulum form of calreticulin modulates glucocorticoid-sensitive gene expression. J. Biol. Chem. 271, 29436.,

Opas et al. 1991: Regulation of expression and intracellular distribution of calreticulin, a major calcium binding protein of non-muscle cells. J. Cell. Physiol. 149, 160.

Michalak et al. 1991: Identification and immunolocalization of calreticulin in pancreatic cells: no evidence for “calciosomes”. Exp. Cell Res. 197, 91.

Papp, et al. 2003: Is all endoplasmic reticulum created equal? The effects of the heterogeneous distribution of ER Ca2+ handling proteins. J. Cell Biol. 160, 475.

“Calreticulin” reviewed in Bedard et al. 2005: Cellular functions of the ER chaperones calreticulin, calnexin and Erp57. Int. Rev. Cytol. 245, 91. and Michalak et al. 2009: Calreticulin, a multi-process calcium buffering chaperone of the endoplasmic reticulum. Biochem. J. 417, 651.


Opas, M. 1987: Transmission of forces between cells and their environment. In: Cytomechanics, Springer Verlag, Heidelberg 273.

Opas, M. 1989: Expression of the differentiated phenotype by epithelial cells in vitro is regulated by both biochemistry and mechanics of the substratum. Dev. Biol. 131, 281.

Opas, M. and E. Dziak. 1994: bFGF-induced transdifferentiation of RPE to neuronal progenitors is regulated by the mechanical properties of the substratum. Dev. Biol. 161, 440.

“Cytomechanics” of differentiation reviewed in Opas, M. 1994: Substratum mechanics and cell differentiation. Int. Rev. Cytol. 150, 119.

Protozoology (“amoebology”)

Opas, M. 1975: Studies on the locomotion of Amoeba proteus. Acta Protozool. 13, 285.

Rinaldi, R. and M. Opas. 1976: Graphs of contracting glycerinated Amoeba proteus. Nature 260, 525.

Opas, M. 1978: Holographic microscopy of glycerination of Amoeba proteus. J. Microsc. 112, 301.

Opas, M. 1980: Actin distribution in Amoeba proteus. Bull. Acad. Pol. Sci. 28, 511.


Opas, M. 1978: Interference reflection microscopy of adhesion of Amoeba proteus. J. Microsc. 112, 215.

Opas, M. and V.I. Kalnins. 1984: Surface reflection interference microscopy: a new method for visualizing cytoskeletal components by light microscopy. J. Microsc. 133, 291.

Opas, M. 1988: Adhesion of cells to protein carpets: do cells feet have to be black? Cell Motility and the Cytoskeleton 11, 178.

Opas, M. 1997: Measurement of intracellular pH and pCa with a confocal microscope. Trends Cell Biol. 7, 75.

Guan et al. 2006: A VR enhanced collaborative system for 3D confocal microscope image processing, visualization and quantification. Int. J. Image & Graphics 6, 231.

Guan et al. 2006: An automatic method for identifying appropriate gradient magnitude for 3D boundary detection of confocal image stacks. J. Microscopy 223, 66.

Guan et al. 2008: Adaptive correction technique for 3D reconstruction of fluorescence microscopy images. Microsc. Res. Techn. 71, 146.

Szabo et al. 2009: Tamoxifen-inducible Cre-mediated calreticulin excision to study mouse embryonic stem cell differentiation. Stem Cells Devel. 18, 187.

Indhumathi et al. 2011: An automatic segmentation algorithm for 3D cell cluster splitting using volumetric confocal images. J. Microsc. 243, 60.

Indhumathi et al 2012: Adaptive-weighted cubic B-spline using lookup tables for fast and efficient axial resampling of 3D confocal microscopy images. Microsc. Res. Tech. 75, 20.