Fig. 5: XBP1s compartmentalizes SEs-related coactivators to nuclear puncta.

Colocalization of transcriptional coactivators P300 (A), BRD4 (B), CDK9 (C), MED1 (D) with Flag-XBP1s (green) in nuclear puncta in A549 cells. Line scans of the colocalization images are depicted by white arrows with quantification (2D intensity histograms) shown to the right, highlighting Pearson’s correlation coefficients (R-values). Areas of colocalization are indicated in yellow. E Representative images of droplet formation of EGFP-XBP1s (488 nm) with mCherry-P300-IDR, mCherry-MED1-IDR, mCherry-BRD4-IDR or mCherry -CDK9-IDR (594 nm). The co-localization of EGFP-XBP1s (green) and mCherry-labeled IDR proteins (red) demonstrates their phase separation compatibility and mutual incorporation into condensates. Localization of active histone markers H3K27ac (F), H3K4me1 (G) and H3K4me3 (H), repressive histone markers H3K9me3 (I) and active RNA POI II S2P (J) and S5P (K) (red)with Flag-XBP1s (green) in A549 cells, which suggested that the condensates formed by XBP1s are associated with the transcriptional activation of target genes. Line scans of the colocalization images are depicted by white arrows with quantification (2D intensity histograms) shown to the right and below, highlighting Pearson’s correlation coefficients (R-values). Areas of colocalization are indicated in yellow.