Repression of barrier genes in aged enterocytes. (A) Results of a Smurf assay in which flies are fed food containing a nonabsorbable blue dye. Fly on the left is 1 day old and has the blue dye is restricted to the digestive tract. Fly on the right is 40 days old, and the blue dye can be seen throughout the entire body. (B) Top four GO terms on genes that gain H3K27me3 signal in aged enterocytes from differential analysis. (C,D) UCSC Genome Browser tracks of chitin synthesis (C) and chitinase (D) genes that form new H3K27me3 domains in aged enterocytes. (E) Row z-score-normalized heatmap of RNAPIIS5P counts over chitin synthesis gene promoters. The first column of each heatmap is the log₂-transformed counts for 1-day-old tissue for each promoter. Row z-scoring is used to present directionality of the change in signal with age. (F,G) UCSC Genome Browser track of Polycomb in 1-day-old guts at the promoter of the Chs2 gene (F) and at Cht9 (G). (H) Heatmap of log₂-transformed counts for Polycomb binding at each chitin synthesis gene promoter.