Fig. 11.

Fig. 11.

Asymmetry in ECS geometry could explain Fgf8a DV gradient. (A) The Fgf8-EGFP gradient in the ECS at midgastrula stage (≈75% epiboly). The normalized fluorescence intensity profile in the ventral-to-dorsal direction (right) was extracted from sum-intensity z-projected confocal images (left). Values are intensity averages across a region at the marginal blastomere (dotted yellow lines); N=10 embryos. Data are mean±s.d. The embryo is oriented as in Fig. 1A (ventral left, dorsal right, animal pole top, vegetal pole bottom; see gray schematic). Reproduced, with permission, from Harish et al. (2023). (B) Simulated de novo Fgf8a gradient and DV concentration profiles at ≈75% epiboly. The concentration profiles in the ventral-to-dorsal direction (right) were computed by averaging concentration values over yz-planes within the marginal region (dashed yellow lines). The model has the same orientation as the embryo in A. Color represents concentrations in nM (see intensity bar on the left) and simulated time of gradient formation (see color intensity bar on the right). Scale bars: 50 μm. (C) Simulated normalized de novo Fgf8a DV concentration profiles at different stages of epiboly (see key). A gradient similar to the one observed in vivo (A) emerges at ≈75% epiboly. The computationally predicted profiles are flat in geometries of 40% and 60% epiboly (gray and cyan lines, respectively). All profiles are computed at . (D) ECS porosity (plus symbols) along the DV axis at different stages of epiboly (see key). At 75% epiboly, the ψ_ECS profile shows a gradient with porosity values approximately halving from ≈0.4 at the ventral to ≈0.2 at the dorsal side. The hypothesis that this could explain the Fgf8a DV gradient is contradicted by the similar ψ_ECS profile at 60% epiboly, which is when the Fgf8a DV profile is flat.