Immunocytochemistry of iPSC-CMs was performed as previously described (34 (link)). Briefly, iPSC-CMs were replaced on 12-mm coverslips coated with poly-d-lysine. After fixation with 4% paraformaldehyde (15 min) and permeabilization with 0.3% Triton X-100 (15 min), coverslips were blocked for 1 hour with 5% goat serum/phosphate-buffered saline. Rabbit anti-RBM20 antibody (Novus Biologicals, NBP2–34038, 1:250), mouse anti-G3BP1 (Proteintech 66486–1-Ig, 1:250), and mouse anti–α-actinin (Sigma-Aldrich, A7811, 1:800) in 5% goat serum/phosphate-buffered saline was applied and incubated overnight at 4°C. Then, coverslips were incubated with fluorescein-conjugated goat anti-rabbit Alexa Fluor 488 and anti-mouse immunoglobulin G (IgG) Alexa Fluor 555 (Invitrogen). Sodium arsenite (1 mM for 1 hour) was used for inducing stress granules. Images were taken by a Zeiss LSM 800 microscope using a 20× objective and N-SIM S Super Resolution Microscope (Nikon) using a 100× oil objective.