Biomechanics of yolk cell endocytosis impaired embryos. (A) Yolk granules flows patterns are altered in rab5ab YMOs. PIV of time-lapse snapshots imaged by two-photon microscopy of a Tg (β-actin:m-GFP) rab5ab YMO (see Supplementary Movies 8, 9). From epiboly onset, yolk granules flows are uncoordinated in rab5ab YMOs. The internal toroidal vortices characteristic of epiboly progression (Hernandez-Vega et al., 2017) do not form or are severely reduced and the laminar flows become asymmetrically distributed. Animal (A) and vegetal (V) poles are indicated. (B) Mechanical power density maps over time obtained by HR analysis in rab5ab YMO (from Supplementary Movie 10). The Relative Mean Square Error (RMSE) of the inferred power maps is shown as a percentage at the top left of each panel expressing the fitting accuracy. Qualitatively, rab5ab YMOs display no differences with wild type embryos in the spatial distribution of mechanical work (Hernandez-Vega et al., 2017) but exhibit a strong delay and an overall decrease of power of about four-fold. Arrow points to the highest power value at 70% epiboly at the E-YSL. Scale bar 25 μm. (C) Longitudinal along the AV axis (red) and latitudinal or circumferential - CC (green) stresses and their differences (blue) along the embryo cortex in a membrane-GFP transgenic [Tg (β-actin:m-GFP)] rab5ab YMO (from Supplementary Movie 12). Stresses were plotted as a function of the φ angle from animal to vegetal (40, 50, and 65% epiboly). The equator - dotted yellow line -, yolk cell surface - purple shadow - and the RMSE of the dynamic pressure (fitting accuracy) as a percentage for each time point are displayed. The latitudinal stress does not steep up from animal to vegetal until 70% epiboly, while the longitudinal stress oscillations are sustained.
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