Anterior and posterior cone cells and 1° cells are mechanically coupled. (A–D) Rho1 overexpression promotes strong fluctuations in F-actin levels and apical cell area that are inversely coordinated between neighboring cells. (A and B) Time series montage showing typical fluctuations in medioapical F-actin and cell area in (A) WT cone cells and (B) cone cells that overexpress Rho1. Green arrows, low F-actin intensity and apical cell area relaxation. Red arrows, high F-actin intensity and apical cell area contraction. (B′) Fluctuations in F-actin levels are negatively correlated between anterior and posterior cone cells that overexpress Rho1 (R = −0.4496, N = 8 pairs from 16 cells, one-sample t test: P = 0.0086). (C and D) Time series montage of medioapical F-actin dynamics and apical cell area fluctuations in (C) WT and (D) Rho1-overexpressing 1° LCs. (D) Fluctuations in F-actin and apical cell area also appear negatively correlated between adjacent 1° LCs expressing Rho1. Scale bar = 3 µm.