In [1]:
import IPython.core.display as disp
%matplotlib inline
2014-06-12 14:09:14,787 -leg_joint -INFO -successfully imported leg_joint

The elementary cell

The architecture of the epithelium model consists of an oriented graph containing

  • two types of vertices:

    • The cells themselves
    • The appical junctions vertices
  • and two types of edges:

    • The junction edges, structuring the apical surface of the epithelium and oriented randomly from one junction vertex to the other

    • The cell to junction edges linking one cell to its neighbouring junction vertices, oriented from the cell vertex to the junctions

In [13]:
image/svg+xml lij A L cell junction edge junction vertex cell to junction edge lij edge length A cell surface L cell perimeter

3D geometry

The position of the vertices is given in two 3D coordinate systems, cartesian $(x, y, z)$ and cylindrical $(\rho, \theta, z)$.

Initialy, the vertices are distributed over a cylinder centered around the $z$ axis. The volume of a cell is computed as the sum of the area of each triangle formed by a junction edge and two cell-to-junction edges times the height of the cell center. Of course this is an approximation: $$ V_\alpha = \sum_{i,j} A_{\alpha ij} h_\alpha c_{\alpha i} c_{\alpha j} c_{ij} $$ with $c_{uv} = 1$ if vertices $u$ and $v$ are connected and 0 otherwise.
and $A_{\alpha ij} = || \mathbf{r}_{\alpha i} \times \mathbf{ r}_{\alpha j} || / 2 $

Interactions at the apical junctions

Three interactions are considered at the epithelium:

  • The line tension between two junction vertices, with associated energy $E^t_{ij} = \Lambda \ell_{ij}$, where $\ell_{ij}$ is the length of the junction edge between vertices $i$ and $j$.

  • The contraction of a cell, with associated energy $E^c_\alpha = \Gamma L_\alpha^2$, where $L_\alpha$ is the perimeter of the cell $\alpha$.

  • The volume elasticity $E^v_\alpha = K_v (V_\alpha - V_0)^2$, where $V_\alpha$ is the volume of the cell $\alpha$.

The total energy is given by:

$$ E = \sum_\alpha (E^v_\alpha + E^c_\alpha) + \sum_{i \leftrightarrow j} E^t_{ij} $$

Coordinate system

In order to have a workable geometric representation of the leg, we discribe it as having a cylindrical symmetry. The reference frame is thus the one bellow:

In [14]:
image/svg+xml proximal distal dorsal ventral anterior posterior y x T3-T4 T4-T5 apical basal ρ θ z

Quickstart with the leg_joint module

Exemple of a simulated epithelium

We show below a view of an epithelium. The static view is stored as a graphXML file parsed by graph_tool, and passed to instenciate an Epithelium container class. We won't focus on the implementation details for now.

In [15]:
eptm = lj.Epithelium(,
2014-06-12 14:46:43,151 -leg_joint.epithelium -INFO -Instanciating epithelium tuto
2014-06-12 14:46:44,396 -leg_joint.epithelium -INFO -Initial cells
2014-06-12 14:46:44,397 -leg_joint.epithelium -INFO -Initial junctions
2014-06-12 14:46:56,058 -leg_joint.epithelium -INFO -Update geometry
<Epithelium with 1729 cells and 5059 junction edges at 0x7fdcfc73fd90>
Identifier : tuto_2014-06-12T12_46_43
Directory : /home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto

The graph attribute

The etm.graph object is a graph-tool Graph instance, so all the associated methods and attributes are accessible, please refer to graph-tool thourough documentation for details.

All the variables associated with the apical junction network are stored as graph_tool PropertyMaps.

In [5]:
ixs            (vertex)  (type: double)
grad_zed       (vertex)  (type: double)
prefered_vol   (vertex)  (type: double)
vols           (vertex)  (type: double)
vol_elasticities (vertex)  (type: double)
perimeters     (vertex)  (type: double)
is_local_vert  (vertex)  (type: bool)
radial_tensions (vertex)  (type: double)
thetas         (vertex)  (type: double)
zeds           (vertex)  (type: double)
is_alive       (vertex)  (type: bool)
grad_wy        (vertex)  (type: double)
rhos           (vertex)  (type: double)
volume_grad_apical (vertex)  (type: double)
grad_ix        (vertex)  (type: double)
contractilities (vertex)  (type: double)
contractile_grad (vertex)  (type: double)
volume_grad    (vertex)  (type: double)
is_active_vert (vertex)  (type: bool)
ages           (vertex)  (type: int32_t)
grad_radial    (vertex)  (type: double)
areas          (vertex)  (type: double)
volume_grad_radial (vertex)  (type: double)
elastic_grad   (vertex)  (type: double)
is_cell_vert   (vertex)  (type: bool)
grad_sigma     (vertex)  (type: double)
wys            (vertex)  (type: double)
sigmas         (vertex)  (type: double)
volume_grad_cell (vertex)  (type: vector<double>)
dwys           (edge)    (type: double)
dsigmas        (edge)    (type: double)
u_dzeds        (edge)    (type: double)
is_local_edge  (edge)    (type: bool)
drhos          (edge)    (type: double)
u_dwys         (edge)    (type: double)
is_junction_edge (edge)    (type: bool)
at_boundary    (edge)    (type: bool)
is_ctoj_edge   (edge)    (type: bool)
edge_lengths   (edge)    (type: double)
dthetas        (edge)    (type: double)
u_dixs         (edge)    (type: double)
is_new_edge    (edge)    (type: bool)
dixs           (edge)    (type: double)
line_tensions  (edge)    (type: double)
u_drhos        (edge)    (type: double)
dzeds          (edge)    (type: double)
u_dsigmas      (edge)    (type: double)
is_active_edge (edge)    (type: bool)

Epithelium objects have an attribute paths with the path to the epithelium directory, where data will be stored.

In [16]:
{'xml': '/home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto/xml',
 'hdf': '/home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto/eptm_tuto_2014-06-12T12_46_43.h5',
 'root': '/home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto',
 'svg': '/home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto/svg',
 'log': 'saved_graphs/tuto/tuto_2014-06-12T12_46_43.log',
 'pdf': '/home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto/pdf',
 'png': '/home/guillaume/Python/leg-joint/notebooks/saved_graphs/tuto/png',
 'json': 'saved_graphs/tuto/params_tuto_2014-06-12T12_46_43.json'}

There are various ways to look at an epithelium. The default one is just called draw, and produces a 3D and a 2D view. Color code corresponds to the depth of the edge.

In [17]:
output3d = os.path.join(eptm.paths['png'], 'tissue_3d.png')
output2d = os.path.join(eptm.paths['png'], 'tissue_2d.png')

In [18]:
In [19]:

Comparison with Farhadifar et al. geometry

For the epithelium above, we can look at the number of neighbors for each cells, and the dependency of the cells' areas on this number. This is what we compute in the cell bellow.

In [12]:

## The number of side is equal to the number of junction vertices
## thus to the number of out neighbors of each cell
num_sides = eptm.graph.degree_property_map('out')

## Filter living cells
live_cells = eptm.is_alive.copy()
live_cells.a *= eptm.is_cell_vert.a

## Computing nomrmalized area
normed_areas = eptm.cells.areas.fa / eptm.cells.areas.fa.mean()

## Getting the numbr of sides only for living cells
num_sides = np.asarray(num_sides.fa)
u_num_sides = np.unique(num_sides)

## Plotting it all
avg_areas = np.zeros(u_num_sides.size)
stm_areas = np.zeros(u_num_sides.size)
bins, n_cells = np.histogram(num_sides, bins=11, range=(0, 11))

for n, n_sides in enumerate(u_num_sides):
    avg_areas[n] = normed_areas[num_sides == n_sides].mean()
    stm_areas[n] = normed_areas[num_sides == n_sides].std() / np.sqrt(n_cells[])
fig, (ax1, ax2) = plt.subplots(2, 1, sharex=True, figsize=(6, 6))
ax1.plot(num_sides, normed_areas, 'o', alpha=0.05)    
ax1.errorbar(u_num_sides, avg_areas, yerr=stm_areas, lw=2, elinewidth=2)
ax1.set_xlim(0, 12)

ax2.hist(num_sides, bins=11, range=(0.5, 11.5),
         normed=True, color='g', alpha=0.7)
ax2.set_xlim(0, 12)
ax2.set_xlabel('Number of cell neighbors')
ax1.set_ylabel('Normalized cell area')

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