Fig. 2.

Trisomy 21 chromosome silencing. a Diagram depicting the development of the inducible system to silence one of the three chromosome 21s in DS patient-derived iPS cells, as initially demonstrated by (Jiang et al. 2013). b Illustration of chromosome 21 gene silencing by XIST RNA. Top panel: Detection of APP RNA transcription foci from three alleles (green) are seen in iPS cell nucleus without Dox induction of XIST (left image). Right panel: Three days after Dox induction a large XIST RNA accumulation (red) has silenced one of the three APP alleles (green). Individual channel showing APP RNA signals with arrow showing absence of a third APP RNA signal where XIST cloud is located and DAPI (blue, shown in black and white) signal showing brighter focus of compacted DNA coincident with XIST RNA cloud. Bottom panel: Induction of XIST RNA with 7 days of Dox produces epigenetic changes on chromosome 21 as shown by H3K27me3 (green) co-localized with XIST RNA (red) and DAPI DNA (blue). B&W image of DAPI staining shows brighter focus of compact DNA (red arrow) coincident with XIST RNA and H3K27me3 signals. Scale bars, 5 µm. c RNAseq affirms that XIST RNA induction decreases expression of genes across the silenced chromosome 21, shown in DS endothelial cells. Red line indicates theoretical one-third reduction in mRNA levels, and vertical black line marks site of XIST insertion. Significant genes are in blue (FDR < 0.05), with other expressed genes in gray (Moon and Lawrence 2022)