(
a) Mitotic cell in the
Drosophila pupal notum labelled with Jupiter:GFP to label MTs (
n=23 cells). White arrows point at astral MTs. Yellow arrowheads indicate spindle poles. Scale bar: 1μm.
(
b) Representation of the different parameters that were varied for the predictions based on the GFP:Mud cortical intensity and shape model to estimate their contribution. L: length of the mitotic spindle,
N: number of astral MTs,
Φ: the angle covered by the astral MTs and
α: the GFP:Mud intensity scaling factor. See also .
(
c-f) Cumulative plots of the differences between the theoretical spindle orientation (
θtheory) and the experimental spindle orientation (
θdivision) angles in GFP:Mud expressing cells (same cells as in ) for different spindle lengths (c), MT number (d), angular extension of astral MTs (e) and different scaling factor between the GFP:Mud intensity and mechanical pulling force (f). The GFP:Mud model predictions are mostly independent of spindle length, the number of astral MTs, the angle covered by the astral MTs or the scaling factor between GFP:Mud intensity and MT pulling force.
(
g) Dependence of model prediction on shape or GFP:Mud effective potential depth (±s.e.m.). The y-axis quantitates the difference between the theoretical angle (
θt) and experimental angle (
θd) (1: aligned, -1: perpendicular). A larger potential depth corresponds to more deformed cells for the shape model, and to a sharp and anisotropic GFP:Mud distribution for the cortical model. Model predictions improve with potential depth, suggesting the model can capture the effect of GFP:Mud distributions in a dose-dependent manner.
n=140 cells
(
h) Definitions of the angles used in the analytical calculation of the contribution of different harmonics to the potential (
U(
θ). The spindle (heavy black line) makes an angle
θ with the positive
x axis. An astral MT (thin black line indicated by the black arrow) projects to the cortex (circle) at an angle
φ with respect to the spindle. The same MT contacts the cortex an angle
β = ψ + θ above the positive
x axis.
(
i) Normalized magnitudes |
ũn|/|
ũ2| of the Fourier coefficients of the kernel
ũ(
Ψ) for
n even. The magnitudes |
ũn| drop off substantially with increasing
n, indicating that for many purposes it should be sufficient to approximate the function
U by its lowest,
n = 2 mode. To calculate numerical values for the Fourier coefficients, we took the average of the normalized spindle length
ϵ =
L/2
R for the 140 cells (
n) analysed in this paper, obtaining
ϵ ≈ 0.76 ± 0.03; because it is difficult to precisely estimate Φ from the available data, coefficients are shown for Φ = 180° and 270° in agreement with the astral MT distribution observed in a.
(
j) Schematic illustrating the difference between cell shape and cell TCJ bipolarity measurements. An elongated cell and a rounded cell are overlaid (left panels) and shown side-by-side (middle and right panels). In this example, although the two cells have distinct shapes, they have the same TCJ bipolarity. The upper panels illustrate the measurement of cell shape, which uses all the pixels making up the cell (blue bars). The lower panels illustrate the measurement of TCJ bipolarity (red bars), which is solely based on the angular distribution of the TCJs (red dots), only using the unit vectors

pointing from the cell center (black dot) to each cell TCJ. The TCJ bipolarity therefore characterizes TCJ distribution independently of cell shape, and a correlation observed between the two quantities is not due to a shape bias in the TCJ bipolarity measurement.