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Propulsion and navigation within the advancing monolayer sheet.

Kim JH, Serra-Picamal X, Tambe DT, Zhou EH, Park CY, Sadati M, Park JA, Krishnan R, Gweon B, Millet E, Butler JP, Trepat X, Fredberg JJ - Nat Mater (2013)

Bottom Line: Here we show that such a relationship between motion and stress is far from direct.Using monolayer stress microscopy, we probed migration velocities, cellular tractions and intercellular stresses in an epithelial cell sheet advancing towards an island on which cells cannot adhere.We found that cells located near the island exert tractions that pull systematically towards this island regardless of whether the cells approach the island, migrate tangentially along its edge, or paradoxically, recede from it.

View Article: PubMed Central - PubMed

Affiliation: School of Public Health, Harvard University, Boston, Massachusetts 02115, USA.

ABSTRACT
As a wound heals, or a body plan forms, or a tumour invades, observed cellular motions within the advancing cell swarm are thought to stem from yet to be observed physical stresses that act in some direct and causal mechanical fashion. Here we show that such a relationship between motion and stress is far from direct. Using monolayer stress microscopy, we probed migration velocities, cellular tractions and intercellular stresses in an epithelial cell sheet advancing towards an island on which cells cannot adhere. We found that cells located near the island exert tractions that pull systematically towards this island regardless of whether the cells approach the island, migrate tangentially along its edge, or paradoxically, recede from it. This unanticipated cell-patterning motif, which we call kenotaxis, represents the robust and systematic mechanical drive of the cellular collective to fill unfilled space.

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Advancing monolayer of MDCK cells encounters and envelops a non-adherent islandA–D: MDCK cells in phase contrast at a sequence of times. In each of these panels, the inset depicts the whole island at the corresponding time point. E–H: Corresponding vectors of instantaneous migration velocities (obtained from PIV) (see Methods). I–L: Migration velocities, <V̄>, averaged over an ensemble of 6 such islands. Three findings are of note. First, fluctuations of velocity are comparable to or exceed local mean values. Second, two points of zero velocity, called stagnation points (red arrows), are evident; the positions of these stagnation points fluctuate in time but reside on average at the equator. Third, as a result, the flow of cells divides into two streams at the upstream stagnation point and merge at the downstream stagnation point. Scale bar in panel (A): 100μm. Velocity scale bars in (E) and (I) applies to (F–H) and (J–L), respectively.
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Figure 1: Advancing monolayer of MDCK cells encounters and envelops a non-adherent islandA–D: MDCK cells in phase contrast at a sequence of times. In each of these panels, the inset depicts the whole island at the corresponding time point. E–H: Corresponding vectors of instantaneous migration velocities (obtained from PIV) (see Methods). I–L: Migration velocities, <V̄>, averaged over an ensemble of 6 such islands. Three findings are of note. First, fluctuations of velocity are comparable to or exceed local mean values. Second, two points of zero velocity, called stagnation points (red arrows), are evident; the positions of these stagnation points fluctuate in time but reside on average at the equator. Third, as a result, the flow of cells divides into two streams at the upstream stagnation point and merge at the downstream stagnation point. Scale bar in panel (A): 100μm. Velocity scale bars in (E) and (I) applies to (F–H) and (J–L), respectively.

Mentions: To perturb the advancing monolayer sheet we deposited a circular pillar of polydimethyl-siloxane (PDMS, diameter = 1mm) upon a polyacrylamide gel (Young’s modulus = 1.2kPa, thickness = 100μm). After coating the gel with collagen I, the pillar was carefully removed to leave a circular island of bare gel upon which cells could not adhere. We then seeded Madin-Darby Canine Kidney (MDCK) epithelial cells 3mm from the island and allowed them to adhere and grow to confluence; growth of a colony of MDCK cells on this substrate is insensitive to substrate stiffness10. After about 3 days, the advancing monolayer encounters (Fig. 1A) and ultimately surrounds this island (Fig. 1B,C,D; Supplementary Fig. S1). Local migration velocity was measured using particle imaging velocimetry (PIV)12 (see Methods). For velocities as well as the other variables reported below, spontaneous fluctuations tend to be as large as or larger than corresponding local mean values. To probe the relationship among the mean values of these variables, we smoothed these fluctuations by averaging each field across an ensemble of six identical monolayer systems and denote such ensemble averages by brackets <…> (see Methods).


Propulsion and navigation within the advancing monolayer sheet.

Kim JH, Serra-Picamal X, Tambe DT, Zhou EH, Park CY, Sadati M, Park JA, Krishnan R, Gweon B, Millet E, Butler JP, Trepat X, Fredberg JJ - Nat Mater (2013)

Advancing monolayer of MDCK cells encounters and envelops a non-adherent islandA–D: MDCK cells in phase contrast at a sequence of times. In each of these panels, the inset depicts the whole island at the corresponding time point. E–H: Corresponding vectors of instantaneous migration velocities (obtained from PIV) (see Methods). I–L: Migration velocities, <V̄>, averaged over an ensemble of 6 such islands. Three findings are of note. First, fluctuations of velocity are comparable to or exceed local mean values. Second, two points of zero velocity, called stagnation points (red arrows), are evident; the positions of these stagnation points fluctuate in time but reside on average at the equator. Third, as a result, the flow of cells divides into two streams at the upstream stagnation point and merge at the downstream stagnation point. Scale bar in panel (A): 100μm. Velocity scale bars in (E) and (I) applies to (F–H) and (J–L), respectively.
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Related In: Results  -  Collection

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Figure 1: Advancing monolayer of MDCK cells encounters and envelops a non-adherent islandA–D: MDCK cells in phase contrast at a sequence of times. In each of these panels, the inset depicts the whole island at the corresponding time point. E–H: Corresponding vectors of instantaneous migration velocities (obtained from PIV) (see Methods). I–L: Migration velocities, <V̄>, averaged over an ensemble of 6 such islands. Three findings are of note. First, fluctuations of velocity are comparable to or exceed local mean values. Second, two points of zero velocity, called stagnation points (red arrows), are evident; the positions of these stagnation points fluctuate in time but reside on average at the equator. Third, as a result, the flow of cells divides into two streams at the upstream stagnation point and merge at the downstream stagnation point. Scale bar in panel (A): 100μm. Velocity scale bars in (E) and (I) applies to (F–H) and (J–L), respectively.
Mentions: To perturb the advancing monolayer sheet we deposited a circular pillar of polydimethyl-siloxane (PDMS, diameter = 1mm) upon a polyacrylamide gel (Young’s modulus = 1.2kPa, thickness = 100μm). After coating the gel with collagen I, the pillar was carefully removed to leave a circular island of bare gel upon which cells could not adhere. We then seeded Madin-Darby Canine Kidney (MDCK) epithelial cells 3mm from the island and allowed them to adhere and grow to confluence; growth of a colony of MDCK cells on this substrate is insensitive to substrate stiffness10. After about 3 days, the advancing monolayer encounters (Fig. 1A) and ultimately surrounds this island (Fig. 1B,C,D; Supplementary Fig. S1). Local migration velocity was measured using particle imaging velocimetry (PIV)12 (see Methods). For velocities as well as the other variables reported below, spontaneous fluctuations tend to be as large as or larger than corresponding local mean values. To probe the relationship among the mean values of these variables, we smoothed these fluctuations by averaging each field across an ensemble of six identical monolayer systems and denote such ensemble averages by brackets <…> (see Methods).

Bottom Line: Here we show that such a relationship between motion and stress is far from direct.Using monolayer stress microscopy, we probed migration velocities, cellular tractions and intercellular stresses in an epithelial cell sheet advancing towards an island on which cells cannot adhere.We found that cells located near the island exert tractions that pull systematically towards this island regardless of whether the cells approach the island, migrate tangentially along its edge, or paradoxically, recede from it.

View Article: PubMed Central - PubMed

Affiliation: School of Public Health, Harvard University, Boston, Massachusetts 02115, USA.

ABSTRACT
As a wound heals, or a body plan forms, or a tumour invades, observed cellular motions within the advancing cell swarm are thought to stem from yet to be observed physical stresses that act in some direct and causal mechanical fashion. Here we show that such a relationship between motion and stress is far from direct. Using monolayer stress microscopy, we probed migration velocities, cellular tractions and intercellular stresses in an epithelial cell sheet advancing towards an island on which cells cannot adhere. We found that cells located near the island exert tractions that pull systematically towards this island regardless of whether the cells approach the island, migrate tangentially along its edge, or paradoxically, recede from it. This unanticipated cell-patterning motif, which we call kenotaxis, represents the robust and systematic mechanical drive of the cellular collective to fill unfilled space.

Show MeSH
Related in: MedlinePlus