Quantifying the shape of cells, from Minkowski tensors to p-atic orders

  1. Lea Happel
  2. Griseldis Oberschelp
  3. Valeriia Grudtsyna
  4. Harish P Jain
  5. Rastko Sknepnek
  6. Amin Doostmohammadi
  7. Axel Voigt  Is a corresponding author
  1. Institute of Scientific Computing, Germany
  2. Niels Bohr Institute, University of Copenhagen, Denmark
  3. Njord Centre, Physics Department, University of Oslo, Norway
  4. School of Life Sciences, University of Dundee, United Kingdom
  5. School of Science and Engineering, University of Dundee, United Kingdom
  6. Center of Systems Biology Dresden, Germany
  7. Cluster of Excellence, Physics of Life, TU Dresden, Germany
29 figures, 2 tables and 1 additional file

Figures

Shape classification of cells in wild-type Madin-Darby canine kidney (MDCK) cell monolayer.

(a) Raw experimental data. (b-f) Minkowski tensor, visualized using ϑp and qp, Equation 7 (see Methods) for p=2,3,4,5,6, respectively. The brightness and the rotation of the p-atic director indicates the magnitude and the orientation, respectively. The visualization uses rotationally symmetric direction fields known as p-RoSy fields in computer graphics (Vaxman et al., 2016). See Appendix 1-Experimental setup for details on the experimental data.

Statistical data for cell shapes identified in Figure 1 (see Methods).

(a) Mean qp¯ and standard deviation σ(qp) of qp. (b- f) Probability distribution function (PDF) of qp for p=2,3,4,5,6, respectively. Kde-plots are used to show the probability distribution.

Schematic description of a two-dimensional object C with contour C.

We denote the center of mass with xc and vectors from xc to points x on C with r. The outward-pointing normals are denoted by n, the corresponding angle with the x-axis by θn.

Regular and irregular shapes, adapted from Armengol-Collado et al., 2023 and Schaller et al., 2024, by Equation 7.

For regular shapes, the corresponding magnitude of qp is always 1.0 and the detected angle is the minimal angle of the p-atic orientation with respect to the x-axis. Note that no shape with q2=1.0 is shown, as this would be a line. The visualization is according to Figure 1.

Illustrative description of the definition of q3 for an equilateral triangle.

Considering rotational symmetries under a rotation 120=2π/3 means that vectors with an angle of 120 or 240 are treated as equal. Applied to the normals n (left), this means that under this rotational symmetry, the normals on the three different edges are equal. Mathematically, this is expressed through e3iθn resulting in the triatic director shown instead of the normals n (middle). One leg of the triatic director always points in the direction as the normal. While only shown for three points on each edge, we obtain an orientation with the respective symmetry on every point of the contour C. Considering the line integral along the contour provides the dominating triadic director, shown in the center of mass (right). To get a value between 0.0 and 1.0 for q3, we normalize this integral with the length of the contour, which corresponds to q0. As all triatic directors point in the same direction, we obtain q3=1.0 in this specific example. To be consistent with other approaches, we rotate the resulting triadic director by 60=π/3 leading to the orange triadic director, which is the quantity used for visualization.

Defining p-atic order for deformable objects requires robust shape descriptors.

Shown is the strength of p-atic order for a polygon converging to an equilateral triangle. (a) using qp and (b) using γp. The considered vectors used in the computations, normals n of the contour for the Minkowski tensors and ri for γp, are shown. Note that the removal of the forth vertex highly influences the value of γp. How xc is calculated - as the mean of the vertex coordinates or as the center of mass of the polygon - can also slightly alter the results. We used the described approach following Armengol-Collado et al., 2023.

Figure 7 with 2 supplements
Nematic (p=2) and hexatic (p=6) orders are independent of each other.

q6 (y-axis) versus q2 (x-axis) for all cells in the multiphase field model (blue) and active vertex model (red). For each cell and each timestep, we plot one point (q2,q6). Each panel corresponds to specific model parameters; Ca and v0 for multiphase field model, and p0 and v0 for the active vertex model, representing deformability and activity, respectively.

Figure 7—figure supplement 1
Distance correlation dCor(q2,q6) between q2 and q6 for all cells in the multiphase field model (MPF - purple box) and active vertex model (AV - green box).

Each panel corresponds to specific model parameters; Ca and v0 for multiphase field model, and p0 and v0 for the active vertex model, representing deformability and activity, respectively. We compute one value for every timestep and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles.

Figure 7—figure supplement 2
P-values of the distance correlation PdCor(q2,q6) between q2 and q6 for all cells in the multiphase field model (MPF - purple box) and active vertex model (AV - green box).

Each panel corresponds to specific model parameters; Ca and v0 for multiphase field model, and p0 and v0 for the active vertex model, representing deformability and activity, respectively. We compute one value for every timestep and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles. 0.05 and 0.1 are marked with a gray dotted/gray dashed line to guide the eye.

Figure 8 with 2 supplements
Nematic (p=2) and hexatic (p=6) order depend on activity and deformability of the cells.

Mean value qp¯ for p=2 (left) and p=6 (right) as function of deformability p0 or Ca and activity v0 for active vertex model (a and b) and multiphase field model (c and d).

Figure 8—figure supplement 1
Nematic (p=2) and hexatic (p=6) order depend on deformability of the cells.

Probability distribution functions (PDFs) for q2 (shades of orange) and (shades of blue), using kde-plots, for varying deformability p0 or Ca and fixed activity v0 . Inlets show mean values of q2 and q6 as function of deformability. (a-d) Active vertex model, (e-h) Multiphase field model for decreasing activity.

Figure 8—figure supplement 2
Nematic (p=2) and hexatic (p=6) order depend on activity of the cells.

Probability distribution functions (PDFs) for q2 (shades of orange) and q6 (shades of blue), using kde-plots, for varying activity v0 and fixed deformability p0 or Ca. Inlets show mean values of q2 and q6 as function of activity. (a-d) active vertex model and (e-h) multiphase field model for decreasing deformability.

Figure 9 with 2 supplements
Coarse-gained nematic (p=2) and hexatic (p=6) order for R/Rcell=8 depend on activity and deformability of the cells.

Mean value Qp¯ for p=2 (left) and p=6 (right) as function of deformability p0 or Ca and activity v0 for active vertex model (a and b) and multiphase field model (c and d).

Figure 9—figure supplement 1
Q6¯ versus Q2¯ for different coarse-graining radii in the active vertex model.

Qp was calculated according to Equation 11, the averaging of this and the choice of Rcell follow the description in Coarse-grained quantities. The maximal coarse-graining radius corresponds to half the domain width. Each panel corresponds to specific model parameters; p0 and v0, representing deformability and activity. A logarithmic scaling was used for both axes. Error bars are obtained as s.e.m.

Figure 9—figure supplement 2
Q6¯ versus Q2¯ for different coarse-graining radii in the multiphase field model.

Qp was calculated according to Equation 11, the averaging of this and the choice of Rcell follow the description in Coarse-grained quantities. The maximal coarse-graining radius corresponds to half the domain width. Each panel corresponds to specific model parameters; Ca and v0, representing deformability and activity. A logarithmic scaling was used for both axes. Error bars are obtained as s.e.m.

Figure 10 with 3 supplements
Nematic (p=2) and hexatic (p=6) order for the cells in the experiments from Armengol-Collado et al., 2023.

(a) Probability distribution functions (PDFs) using kde-plots, for q2 (yellow) and q6 (blue), once using the polygonal approximation of the cell shape and once using the detailed cell outline obtained from the microscopy pictures. (b) q6 (y-axis) versus q2 (x-axis) for all cells from the experimental data in Armengol-Collado et al., 2023, once using the polygonal approximation of the cell shape (blue) and once using the detailed cell outline obtained from the microscopy pictures (red). For each cell and each timestep, we plot one point (q2,q6).

Figure 10—figure supplement 1
Experimental image, segmented cell outline and polygonal shape.

Cell shapes in the experiments from Armengol-Collado et al., 2023. (a) Cell shapes used for the shape quantification, (b) Detailed cell outline obtained from the microscopy image, (c) Polygonal approximation of the cell shape. Shown for frame number 1.

Figure 10—figure supplement 2
Distance correlation dCor(q2,q6) between q2 and q6.

On the left side (a) we use the polygonal approximation of the cell shape, on the right side (b) we use the detailed cell outline obtained from the microscopy pictures. We compute one value for every frame and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles.

Figure 10—figure supplement 3
P-values of the distance correlation PdCor(q2,q6) between q2 and q6.

On the left side (a) we use the polygonal approximation of the cell shape, on the right side (b) we use the detailed cell outline obtained from the microscopy pictures. We compute one value for every frame and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles. 0.05 and 0.1 are marked with a gray dotted/gray dashed line to guide the eye.

Q6¯ versus Q2¯ for different coarse-graining radii for the experimental data from Armengol-Collado et al., 2023.

On the left side (a) we use the polygonal approximation of the cell shape, on the right side (b) we use the detailed cell outline obtained from the microscopy pictures. Qp was calculated according to Equation 11, the averaging of this and the choice of Rcell follow the description in Coarse-grained quantities. The maximal coarse-graining radius corresponds to half the domain width. A logarithmic scaling was used for both axes. Error bars are obtained as s.e.m.

Mean value |γp|¯ as function of deformability p0 and activity v0 for active vertex model.

(a) nematic order (p=2), (b) hexatic order (p=6).

|Γ6|¯ versus |Γ2|¯ for different coarse-graining radii for the experimental data from Armengol-Collado et al., 2023.

We use only the polygonal approximation of the cell shape as γp can only work with polygons. Qp was calculated according to Equation 12, the averaging of this and the choice of Rcell follow the description in Coarse-grained quantities. The maximal coarse-graining radius corresponds to half the domain width. A logarithmic scaling was used for both axes. Error bars are obtained as s.e.m.

Appendix 1—figure 1
Illustration of the active vertex model.

(a) Cell contour of the active vertex model. Red arrows represent the polarity vectors that set each cell’s instantaneous direction of self-propulsion. (b) Zoom in on a vertex surrounded by three cells showing how the direction of self-propulsion on a vertex is calculated.

Appendix 1—figure 2
Illustration of the multiphase field model.

(a) Cell contours of the multiphase field model. (b) Corresponding phase field functions along the horizontal line in (a). Colours correspond to the ones in (a).

Appendix 2—figure 1
PDFs for q3 using kde-plots, for varying deformability p0 or Ca and fixed activity v0.

Inlets show mean values of q3 as function of deformability. (a-d) Active vertex model, (e-h) Multiphase field model for decreasing activity.

Appendix 2—figure 2
PDFs for q4 using kde-plots, for varying deformability p0 or Ca and fixed activity v0.

Inlets show mean values of q4 as function of deformability. (a-d) Active vertex model, (e-h) Multiphase field model for decreasing activity.

Appendix 2—figure 3
PDFs for q5 using kde-plots, for varying deformability p0 or Ca and fixed activity v0.

Inlets show mean values of q5 as function of deformability. (a-d) Active vertex model, (e-h) Multiphase field model for decreasing activity.

Appendix 2—figure 4
PDFs for q3 using kde-plots, for varying activity v0 and fixed deformability p0 or Ca.

Inlets show mean values of q3 as function of activity. (a-d) Active vertex model and (e-h) Multiphase field model for decreasing deformability.

Appendix 2—figure 5
PDFs for q4 using kde-plots, for varying activity v0 and fixed deformability p0 or Ca.

Inlets show mean values of q4 as function of activity. (a-d) Active vertex model and (e-h) Multiphase field model for decreasing deformability.

Appendix 2—figure 6
PDFs for q5 using kde-plots, for varying activity v0 and fixed deformability p0 or Ca.

Inlets show mean values of q5 as function of activity. (a-d) Active vertex model and (e-h) Multiphase field model for decreasing deformability.

Appendix 2—figure 7
Mean value qp¯ for p=3 (left), p=4 (middle) and p=5 (right) as a function of deformability p0 or Ca and activity v0 for active vertex model (a-c) and multiphase field model (d-f).
Appendix 2—figure 8
Regular and irregular shapes, adapted from Armengol-Collado et al., 2023, with magnitude and orientation calculated by Equation 8 and Equation 9.

The brightness scales with the magnitude |γp|.

Appendix 2—figure 9
Shape classification of cells in wild-type Madin-Darby canine kidney (MDCK) cell monolayer.

(a) Raw experimental data. (b-f) Polygonal shape classification, visualized using γp calculated by Equation 8 and Equation 9 for p=2,3,4,5,6, respectively. The brightness and the rotation of the p-atic director indicates the magnitude and the orientation, respectively. See Appendix 1-Experimental setup for details on the experimental data.

Appendix 2—figure 10
Statistical data for cell shapes identified in Appendix 2—figure 9.

(a) Mean |γp|¯ and standard deviation σ(|γp|) of |γp|. (b- f) Probability distribution function (PDF) of |γp| for p=2,3,4,5,6, respectively. Kde-plots are used to show the probability distribution. For this first analysis, we regard only one frame with 235 cells.

Appendix 2—figure 11 with 2 supplements
|γ6| (y-axis) versus |γ2| (x-axis) for all cells in the active vertex model.

For each cell and each timestep, we plot one point (|γ2|,|γ6|). Each panel corresponds to specific model parameters p0 and v0, representing deformability and activity.

Appendix 2—figure 11—figure supplement 1
Distance correlation dCor(|γ2|,|γ6|) for the simulation data of the active vertex model.

Each panel corresponds to specific model parameters p0 and v0, representing deformability and activity. We compute one value for every timestep and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles.

Appendix 2—figure 11—figure supplement 2
P-values of the distance correlation PdCor(|γ2|,|γ6|) for the simulation data of the active vertex model.

Each panel corresponds to specific model parameters p0 and v0, representing deformability and activity. We compute one value for every timestep and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles. 0.05 and 0.1 are marked with a gray dotted/gray dashed line to guide the eye.

Appendix 2—figure 12 with 1 supplement
Coarse-Grained nematic (p=2) and hexatic (p=6) order for R/Rcell=8 depending on activity and deformability of the cells.

|Γp|¯ as function of deformability p0 and activity v0 for active vertex model. (a) nematic order (p=2), (b) hexatic order (p=6).

Appendix 2—figure 12—figure supplement 1
Γ6¯ versus Γ2¯ for different coarse-graining radii in the active vertex model.

Γp was calculated according to Equation 12, the averaging of this and the choice of Rcell follow the description in Coarse-grained quantities. The maximal coarse-graining radius corresponds to half the domain width. Each panel corresponds to specific model parameters: p0 and v0, representing deformability and activity. A logarithmic scaling was used for both axes. Error bars are obtained as s.e.m.

Appendix 2—figure 13 with 2 supplements
Nematic (p=2) and hexatic (p=6) order for the cells in the experiments from Armengol-Collado et al., 2023.

We use the polygonal approximation of the cell shape as γp can only work with polygons. (a): Probability distribution functions (PDFs) using kde-plots, for |γ2| (orange) and |γ6| (blue). (b): Nematic (p=2) and hexatic (p=6) order are independent of eachother. |γ6| (y-axis) versus |γ2| (x-axis) for all cells. For each cell and each timestep, we plot one point (|γ2|,|γ6|).

Appendix 2—figure 13—figure supplement 1
Distance correlation dCor(|γ2|,|γ6|) for all cells from the experimental data in Armengol-Collado et al., 2023.

We use the polygonal approximation of the cell shape as γp can only work with polygons. We compute one value for every frame and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles.

Appendix 2—figure 13—figure supplement 2
P-value of the distance correlation PdCor(|γ2|,|γ6|) for all cells from the experimental data in Armengol-Collado et al., 2023.

We use the polygonal approximation of the cell shape as γp can only work with polygons. We compute one value for every frame and present the resulting distribution with a box plot. In the box plots, the orange line corresponds to the median of the data and the box ranges from the first to the third quartile of the data. The whiskers go from the lowest data point greater than (value of the first quartile) − 1.5 × (Interquartile range) to the highest data point below (value of the third quartile) + 1.5 × (Interquartile range). Outliers are shown with circles.

Author response image 1
Screenshot from p6 = 3.

5 and v0 = 0.1

Tables

Appendix 1—table 1
Values of the dimensionless parameters used in the active vertex model.
ParameterDescriptionNumerical value
NNumber of cells100
LSimulation box size10
TTotal simulation time300
kPPerimeter elastic modulus1.0
τSimulation time step0.01
v0Self-propulsion strength (i.e. activity)0.1–0.4
DrRotation diffusion coefficient0.05
p0Shape index of active cells3.5–3.875
Appendix 1—table 2
Values of the dimensionless parameters used in the multiphase field model.
ParameterDescriptionNumerical value
NNumber of cells100
LSimulation box size100
TTotal simulation time150
ϵInterface width0.15
τSimulation time step0.005
v0Self-propulsion strength (i.e. activity)0.4–1.0
DrRotation diffusion coefficient0.01
αAlignment parameter0.1
CaCapillary number0.05–0.2
InInteraction number0.1
aaCell-cell attraction strength1.0
arCell-cell repulsion strength1.0
hMesh size5hϵ

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  1. Lea Happel
  2. Griseldis Oberschelp
  3. Valeriia Grudtsyna
  4. Harish P Jain
  5. Rastko Sknepnek
  6. Amin Doostmohammadi
  7. Axel Voigt
(2025)
Quantifying the shape of cells, from Minkowski tensors to p-atic orders
eLife 14:RP105680.
https://doi.org/10.7554/eLife.105680.3