Figure 2.
Response of AS Cells to Ectopic Mechanical Stretch
(A) Schematic showing the principle of the stretching experiments. Embryos are compressed using a coverslip. Changes in embryo aspect ratio lead to an increase in interface tension and a stretching of the AS tissue.
(B) Graph showing the apical cell surface area as a function of time for 3 individual cells before and during stretch. The onset of stretch is marked with a dashed line. Upon stretch, we observe an increase of the apical cell surface areas and an arrest of the oscillations.
(C) Graph showing the average distance between the cell boundary and the center of mass (extracted during the scaled average cell methodology) as a function of the angle from the anterior-posterior (AP) axis for average cells before (blue) and during stretch (Red). Upon stretch, we observe a homogeneous increase in centroid-boundary distance that is independent of the angle. Error bars show standard deviations. n = 58 cells on 5 embryos.
(D) Time-lapse sequence showing AS cell kinetics of embryos expressing Tomato-E-cadherin and Sqh-GFP before, during, and after application of stretch. (Top) Before stretch, AS cells display myosin foci propagating through the medial area and a consequent pulsatile activity. (Middle) During stretch, AS cell apical surface area is approximately constant, the myosin foci are not present anymore, and myosin localizes preferentially at junctions. (Bottom) Immediately after stress release, myosin flows from the junctions to the medial area in a coordinated manner, generating a concerted decrease in cell area. Scale bar: 10 μm.
(E) (Left) Scaled average cells over time for WT cells during stretch (Top-Left) and after release (Bottom-Left); and (Right) corresponding kymographs showing myosin distribution within the gray box (averaged horizontally) over time. We observe a progressive enrichment at the junction with time under stretch and flows from the junction to the middle of the cell after stress release. NWTstretch = 58 cells on 5 embryos and NWTrelease = 61 cells on 6 embryos.
(F) Graph showing the normalized junctional myosin concentration and normalized perimeter over time during stretch for cells experiencing a stretch larger than 9%. Junctional myosin is defined as myosin intensity measured within a 3-pixel width path following the E-cadherin-stained junction. Myosin levels are normalized to the myosin levels at the onset of the stretch. Perimeter is normalized by the perimeter before stretch. Error bars show standard deviations. N = 14 cells on 4 embryos.
(G) Time sequence showing an adherens junction experiencing ectopic stretch in an embryo expressing Tomato-E-cadherin and Sqh-GFP. After stretch, myosin levels at the junction increase, and junctional length reduces to approximately similar length than before stretch was applied. Scale bar: 2 μm.