Figure 4. The mechanosensitivity of c4da to lateral tension.

(A) The responses of c4da (ΔF/F₀) to the d-off stimuli (4 mN, 60 μm probe) applied at different positions.The numbers of cells were indicated below the scattered data points. Mann Whitney U test was used. **: p<0.01. *: p<0.05. ns: no significance. Genotype: ppk-gal4/+; ppk-cd4-tdtom/20×uas-ivs-gcamp6s. (B) Left panel: representative heat maps showing the 2D distributions of pressure perpendicular to the cuticle surface (P_P) and tension parallel with the cuticle surface (T_L) of the 30 μm (upper) and 60 (lower) μm probes. Scale bar, 30 μm. Right panels: representative line profiles (normalized) showing the distribution of P_P and T_L versus the distance to the center of the force probe. Indentation depth: 20 μm. (C) The representative color map for the distance to the nearest dendrite, in which the distance was color-coded as indicated. Random positions were chosen (the red crosses) as the force application points in our simulations. Scale bar, 100 μm. (D–E) The activation probability in three conditions: (1) only sensitive to P_P; (2) only sensitive to T_L; (3) sensitive to both P_P and T_L. The dendritic coverage threshold (C_d) was the minimal length of activated dendrites that could excite neuronal responses. For each condition, 100 random positions and two sizes of probes (panel D) 30 μm; (panel E) 60 μm were used in our simulations for each cell (n=5 cells). In panel (A), (D) and (E), data were presented as mean ± std.

Figure 4—figure supplement 1. Mechanical modeling analysis on the distribution of P_P and T_L.

(A) Cartoon schematics for the mechanical model used in the finite element analysis. P_P, pressure perpendicular to the cuticle surface. T_L, tension parallel with the cuticle surface. (B) Representative line profiles (normalized) showing the distribution of P_P and T_L versus the distance to the center of the force probe. Two values of cuticle elastic modulus (1 and 10 MPa) were used to evaluate their effects on the simulation results. We found that in these two cases, the distributions of P_P and T_L were nearly unchanged. Indentation depth: 20 μm. (C) The activation probability (E_cuticle = 1 MPa) in three conditions: (1) only sensitive to P_P; (2) only sensitive to T_L; (3) sensitive to both P_P and T_L. The dendritic coverage threshold (C_d) is the minimal length of activated dendrites that could excite neuronal responses. For each condition, 100 random positions were simulated for each cell (n=5 cells).