Fig. 1: Light-activated condensates sequester specific mRNAs.

A Schematic diagrams of the optoMCP-FUS system. optoMCP-FUS consists of stdMCP, Cry2PHR, mCherry and the N-terminal IDR of FUS. Upon blue light exposure, optoMCP-FUS undergoes phase separation to form condensates that specifically recruit the MBS-tagged mRNAs. B Representative confocal images of the MEF cells expressing optoMCP-FUS during blue light activation and deactivation. The cell is imaged and activated every 2 s. See also Supplementary Movie S1 and S2. C Temporal evolution of the integrated fluorescence intensity of light-activated condensates shown in (B). D Two-color fluorescence images of fixed MEF cells, with the MBS-tagged β-actin gene, expressing optoMCP-FUS (top) and optoFUS (bottom). The MBS-tagged β-actin mRNAs, visualized with smFISH (green), and light-activated condensates (magenta) are shown. Arrowheads indicate individual β-actin mRNA molecules. E Fraction of mRNAs recruited into the light-activated condensates. After 20 min of blue light activation, the recruitment of mRNAs into light-activated condensates was quantified from smFISH data. n = 12 cells for optoMCP-FUS and n = 11 for optoFUS cells. Data are mean ± SD. F The degree of condensate formation as a function of the expression level of optoMCP-FUS. For individual MEF cells, the integrated intensity of the optoMCP-FUS condensates after 15 min of blue light activation is plotted against the initial cytoplasmic intensity of optoMCP-FUS. Arrows indicate individual cells shown in (G) and (H). G Temporal evolution of the integrated intensity of optoMCP-FUS condensates after blue light exposure. H Confocal images of MBS-KI (top) and WT MEF cell (bottom) expressing optoMCP-FUS. I Time-lapse confocal images showing fusion events between optoMCP-FUS condensates. J Confocal images of an optoMCP-FUS condensate (top) and the fluorescence recovery curve (bottom) in FRAP experiments. Cells were activated every 15 s to induce phase separation. A white dashed circle indicates a bleached area. n = 14 cells. Data are mean ± SD. Scale bars, 10 μm (B, D, and H), 2 μm (zoomed-in image in D and I), and 1 μm (J). a.u., arbitrary units. Source data for panels C, E–G, and J are provided in the Source Data file.