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. 2023 Jan 4;9(1):eabn5429. doi: 10.1126/sciadv.abn5429

Fig. 2. Characterization of gastrulation in embryos after perturbation of the BMP/Wnt and Vegf signalling pathways.

Fig. 2.

(A) Bright-field image of embryo treated with the BMP receptor inhibitor LDN (100 nM) and the GSK3 inhibitor CHIR (3 μM) for 16 hrs from stage HH1 onward (time after which control embryos reach stage HH3+). The embryos generate a large circular invagination that engulfs the central epiblast. (B) SNAI2 expression in the embryo shown in (A). (C) Two sections taken at the white lines in (A) showing SNAI (green), FN1 (red), and actin (blue). Note that the FN1 layer is not fragmented at the site of invagination. (D) Lightsheet microscope overview image of an embryo at the end of the experiment overlaid with a deformation mesh (typical for four of five embryos in the light sheet microscope). (E) Strain rate tensor for the embryo shown in (D). Isotropic strain rate component shown as color blue for contraction and red for expansion. The anisotropic part of the strain rate tensor is shown as black and white bars indicating the magnitude and direction of contraction. (F) Cells that will ingress through the streak [domain of attraction (DOA)] during the experiment calculated from the dynamic morphoskeleton (DM). (G) Schematic of the development of a contractile ring which in the absence of EMT results in the invagination of the central epiblast. (H to N) Same layout as (A) to (F) for embryos treated for 16 hrs with the vascular endothelial growth factor (VEGF) receptor inhibitor axitinib (100 nM). (H) Bright field image of axinitib treated embryo. (I) SNAI2 expression in embryo shown in (H). Axinitib treated embryos show limited breakdown of FN1 in the posterior streak (J), an inhibition of the isotropic contraction in the region of the primitive streak (L), a pronounced folding in the anterior streak (K) and a reduced ingression of mesendoderm cells in the streak (M) (four of five in the light sheet microscope). (N) Schematic of the formation of the primitive streak, which in the absence of EMT buckles into the embryo.