Fig. 2
The motion of cytoplasmic F-actin directly correlates with the motion of vesicles. a Confocal image of F-actin stained by UTRN.GFP (left panel). DIC image of the same oocyte (right panel). n nucleus. Scale bar is 30 µm. b Distribution of F-actin (stained with TRITC-phalloidin) in a fixed st9 egg chamber. b′ High magnification of cytoplasmic F-actin (white box in b). c UTRN.GFP-expressing living egg chamber. UTRN.GFP labels the same structures as phalloidin in fixed samples (compare to b). c′ High magnification of cytoplasmic F-actin in a UTRN.GFP-expressing living oocyte (white box in c). b′, c′ Scale bars represent 10 µm. d Intermediate scattering functions (ISF) f(q,Δt) obtained from Con-DDM analysis for different wave vectors q in the range 2 µm−1 < q < 8 µm−1. Continuous lines are best fit to Eq. (1). e Decorrelation rates Γ 1(q) (solid triangles) and Γ 2(q) (open triangles) obtained from the fit of the ISF, represented in d. Dashed line constitutes the best fit of Γ 1(q) to a linear function Γ 1(q) = v act q. Continuous line is obtained from the fit of Γ 2(q) to a quadratic function Γ 2(q) = D act q 2. f F-actin mean speeds (v act) plotted against vesicle mean speeds (v ves) with each data point corresponding to one cell. The continuous line represents v act = v ves. g F-actin diffusion coefficients (D act) plotted against vesicles diffusion coefficients (D ves). Each data point corresponding to one cell. The continuous line corresponds to D act = 2D ves. h D act (green triangles) and D ves (black boxes) as a function of the respective mean speeds v act and v ves. While v act and v ves are similar for each cell, D act is consistently higher (∼twofold) compared to D ves. Horizontal solid lines represent D act,nf and D ves,nf, obtained from colchicine-treated cells, showing no persistent motion (green—F-actin, black—vesicles, also compare to Fig. 3). Dashed areas correspond to mean value ± sd. These values agree remarkably well with the extrapolated behavior for v → 0 of the experimental data obtained from control cells (dashed lines). The horizontal dotted line corresponds to the estimated value of the thermal diffusion coefficient D TH of the vesicles, characterizing their spontaneous fluctuation in the absence of any active process
