Fig. 6
From: Mechanical impact of epithelial−mesenchymal transition on epithelial morphogenesis in Drosophila
An apico-basal force drives mesoderm invagination. Schemes recapitulate the orientation of the embryos and the laser cuts performed in each experiment. a Longitudinal views of sqhKI[eGFP] control embryos (n = 17), showing the linear shape of the invagination front at early stage. b (top) Longitudinal views of sqhKI[eGFP] embryo ablated in the mid-plane region (red rectangle in the scheme and a dashed magenta line in the figure, n = 12), showing a slight delay in the central region compared to the anterior one, as shown by the outline of the invagination front in magenta at early stage of invagination. (bottom) Scheme of the invagination fronts in the control (white line, as in a) and ablated embryo (magenta line). c Anterior (left) and central (right) transversal views of a mid-plane ablated embryo, at two different times of the invagination. Note that invagination proceeds normally as shown by the V-shaped invagination outlined by a white dotted line (bottom), although a delay in the central region can be observed at early stage (top, compare anterior to central region). d Ventral and transversal views extracted from a movie of a control sqhKI[eGFP] embryos, showing the different step of mesoderm invagination. e The apical surface was cut on the anterior and the posterior sides (blue arrowheads, see left schemes) to isolate the central domain of the mesoderm. Note that the invagination is taking place normally, in term of invagination shape, depth and timing (n = 10). f After isolation of the central domain (apical cuts as described in e), ablation was performed in the mid-plane of the central region of the mesoderm (red rectangle on the scheme, magenta dashed line in the figure). Note that the invagination is totally prevented when apico-basal forces are impaired in the vast majority of the cases (n = 11/12). e, f Note that apical constriction occurs in both cases, as shown by the curved shape adopted by the ventral surface (white arrowheads). Apico-basal cables are not visible due to low resolution. Scale bar: 10 µm. An anterior, P posterior, V ventral, D dorsal, Ap apical, B basal. See also Supplementary Figs. 2, 3 and Supplementary Movie 8
