Limits...
Monolayer stress microscopy: limitations, artifacts, and accuracy of recovered intercellular stresses.

Tambe DT, Croutelle U, Trepat X, Park CY, Kim JH, Millet E, Butler JP, Fredberg JJ - PLoS ONE (2013)

Bottom Line: To assess the validity of these assumptions and to quantify associated errors, here we report new analytical, numerical, and experimental investigations.For several commonly used experimental monolayer systems, the simplifying assumptions used previously lead to errors that are shown to be quite small.Out-of-plane components of displacement and traction fields can be safely neglected, and characteristic features of intercellular stresses that underlie plithotaxis remain largely unaffected.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA. dhananjay@alumni.brown.edu

ABSTRACT
In wound healing, tissue growth, and certain cancers, the epithelial or the endothelial monolayer sheet expands. Within the expanding monolayer sheet, migration of the individual cell is strongly guided by physical forces imposed by adjacent cells. This process is called plithotaxis and was discovered using Monolayer Stress Microscopy (MSM). MSM rests upon certain simplifying assumptions, however, concerning boundary conditions, cell material properties and system dimensionality. To assess the validity of these assumptions and to quantify associated errors, here we report new analytical, numerical, and experimental investigations. For several commonly used experimental monolayer systems, the simplifying assumptions used previously lead to errors that are shown to be quite small. Out-of-plane components of displacement and traction fields can be safely neglected, and characteristic features of intercellular stresses that underlie plithotaxis remain largely unaffected. Taken together, these findings validate Monolayer Stress Microscopy within broad but well-defined limits of applicability.

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Balance of forces considered in MSM.(a) Cell monolayer is considered as a thin sheet of cells. Each cell in the monolayer exerts traction, , on the substrate. According to the Newton's second law, the tractions are balanced by local monolayer stress, , such that, in the one dimensional force balance, . (b) The force balance is ensured only in the  plane. Variation of stresses across the thickness is assumed to be negligible. (c) In classical wound healing assay, also referred to as case 2, the optical field-of-view has three optical edges and a free edge. For boundary conditions, all edges have shear stress to be zero. In addition, the free edge has normal stress to be zero and the optical edge has normal displacement to be zero.
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pone-0055172-g001: Balance of forces considered in MSM.(a) Cell monolayer is considered as a thin sheet of cells. Each cell in the monolayer exerts traction, , on the substrate. According to the Newton's second law, the tractions are balanced by local monolayer stress, , such that, in the one dimensional force balance, . (b) The force balance is ensured only in the plane. Variation of stresses across the thickness is assumed to be negligible. (c) In classical wound healing assay, also referred to as case 2, the optical field-of-view has three optical edges and a free edge. For boundary conditions, all edges have shear stress to be zero. In addition, the free edge has normal stress to be zero and the optical edge has normal displacement to be zero.

Mentions: We consider a monolayer comprising a collection of contiguous cells which forms a sheet that is flat and thin (Fig. 1a). By flat and thin we mean that, compared with the lateral span () of the monolayer, its radius of out-of-plane curvature is large and its height () is small. In that case, stresses within the monolayer () and underlying tractions exerted by the monolayer upon its substrate () are taken to be planar with no out-of-plane contributions (, Fig. 1b); the contribution of out-of-plane tractions, and the accuracy of in-plane traction recovery is assessed in Results and Discussion.


Monolayer stress microscopy: limitations, artifacts, and accuracy of recovered intercellular stresses.

Tambe DT, Croutelle U, Trepat X, Park CY, Kim JH, Millet E, Butler JP, Fredberg JJ - PLoS ONE (2013)

Balance of forces considered in MSM.(a) Cell monolayer is considered as a thin sheet of cells. Each cell in the monolayer exerts traction, , on the substrate. According to the Newton's second law, the tractions are balanced by local monolayer stress, , such that, in the one dimensional force balance, . (b) The force balance is ensured only in the  plane. Variation of stresses across the thickness is assumed to be negligible. (c) In classical wound healing assay, also referred to as case 2, the optical field-of-view has three optical edges and a free edge. For boundary conditions, all edges have shear stress to be zero. In addition, the free edge has normal stress to be zero and the optical edge has normal displacement to be zero.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585344&req=5

pone-0055172-g001: Balance of forces considered in MSM.(a) Cell monolayer is considered as a thin sheet of cells. Each cell in the monolayer exerts traction, , on the substrate. According to the Newton's second law, the tractions are balanced by local monolayer stress, , such that, in the one dimensional force balance, . (b) The force balance is ensured only in the plane. Variation of stresses across the thickness is assumed to be negligible. (c) In classical wound healing assay, also referred to as case 2, the optical field-of-view has three optical edges and a free edge. For boundary conditions, all edges have shear stress to be zero. In addition, the free edge has normal stress to be zero and the optical edge has normal displacement to be zero.
Mentions: We consider a monolayer comprising a collection of contiguous cells which forms a sheet that is flat and thin (Fig. 1a). By flat and thin we mean that, compared with the lateral span () of the monolayer, its radius of out-of-plane curvature is large and its height () is small. In that case, stresses within the monolayer () and underlying tractions exerted by the monolayer upon its substrate () are taken to be planar with no out-of-plane contributions (, Fig. 1b); the contribution of out-of-plane tractions, and the accuracy of in-plane traction recovery is assessed in Results and Discussion.

Bottom Line: To assess the validity of these assumptions and to quantify associated errors, here we report new analytical, numerical, and experimental investigations.For several commonly used experimental monolayer systems, the simplifying assumptions used previously lead to errors that are shown to be quite small.Out-of-plane components of displacement and traction fields can be safely neglected, and characteristic features of intercellular stresses that underlie plithotaxis remain largely unaffected.

View Article: PubMed Central - PubMed

Affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA. dhananjay@alumni.brown.edu

ABSTRACT
In wound healing, tissue growth, and certain cancers, the epithelial or the endothelial monolayer sheet expands. Within the expanding monolayer sheet, migration of the individual cell is strongly guided by physical forces imposed by adjacent cells. This process is called plithotaxis and was discovered using Monolayer Stress Microscopy (MSM). MSM rests upon certain simplifying assumptions, however, concerning boundary conditions, cell material properties and system dimensionality. To assess the validity of these assumptions and to quantify associated errors, here we report new analytical, numerical, and experimental investigations. For several commonly used experimental monolayer systems, the simplifying assumptions used previously lead to errors that are shown to be quite small. Out-of-plane components of displacement and traction fields can be safely neglected, and characteristic features of intercellular stresses that underlie plithotaxis remain largely unaffected. Taken together, these findings validate Monolayer Stress Microscopy within broad but well-defined limits of applicability.

Show MeSH
Related in: MedlinePlus