Spatial organization of ALK3 from BMPRII in focal adhesions. (A) Schematic of whether crosstalk between integrin and BMPR relies on proximal interaction at the cell membrane (left panel). Fluorescent and optogenetic tools are used to image BMPRs and β3 integrin and to control BMPR/β3 integrin proximity respectively. ALK3 is given as an example of BMPR (right panel). Optogenetic tool (iLID/SspB) allowing the blue light-induced intracellular interaction between β3 integrin and ALK3 is shown, as an example. (B) Opto-BMPRs-RFP and opto-β3 integrin-Venus are coexpressed in MEFsv40 and visualized by TIRF-mode imaging. Without BMP2 treatment, BMPRs were localized throughout the cell surface and β3 integrin was targeted to FAs. (C) sBMP2 treatment induces spatial segregation of ALK3 from BMPRII at adhesion sites. Scale bar 15 µm. (D) Quantification of the ratio of the level of recruitment inside and outside focal adhesions, identified by β3 integrin (Venus tag), on cells expressing ALK3, BMPRII, or CAAX (RFP tag) upon BMP2 stimulation. N ≥ 14 cells per condition.