Figure 1. RhoA-Mediated Tension Determines Junction Length at Short Timescales.

(A) Schematic of TULIP optogenetic system. Blue light activation causes recruitment of prGEF to the plasma membrane.

(B) Quantification of the local intensity increase of mCherry-prGEF in the junctional activation region shown in (C) (magenta). Activation period is indicated by the gray box.

(C) Representative images of cells undergoing junctional prGEF (magenta) recruitment. prGEF rapidly accumulates at the junction and dissociates upon light inactivation. Scale bar, 10 μm.

(D) Representative images of a junction undergoing a 5-min activation. Junctions undergo rapid contraction upon prGEF recruitment that is reversible upon its removal. Red lines denote positions and lengths between the two junction vertices. Scale bar, 10 μm.

(E) Normalized junction length over time with a 5-min activation shows junction contraction during activation (gray). Individual trials are in a dashed line with the average in a solid line. The magenta line represents data shown in (D).

(F) Plot of the fractional contracted length after a 5-min activation, L₅/L₀, as a function of the initial junction length.

(G) Normalized junction length over time of cells treated with Y-27632.

(H) Representative kymograph of a junction (visualized by Cell Mask) prior to, during, and after a 5-min activation. The red dashed lines denote fiduciary marks within a junction. The blue region denotes the junction length; the red portion indicates a region that contracts. Horizontal scale bar, 6 min and vertical scale bar, 5 μm.

(I) The location of the contractile regions for 11 distinct junctions, indicated by a unique junction number. The junction length is normalized such that the top vertex is denoted by 1, with the bottom vertex denoted by 0. The junction in 1H is depicted by the blue line.

(J) Normalized junction length over time of junctions in a 5-min activation with light targeted only to the junction center.