Figure 7

A schematic representation of transcription initiation (ti)RNA sponge effects on the p21 (cyclin-dependent kinase inhibitor 1A gene, also known as CDKN1A ) and StAR-related lipid transfer domain containing 13 ( STARD13 ) loci. (a) The p21 CCCTC-binding factor (CTCF) proximal (cp)-tiRNA sponge removes tiRNAs from the system, which in turn facilitates increased CTCF binding and, consistent with the literature, increased nucleosome ordering and density. CTCF-adjacent nucleosomes are known to be enriched for the H3K4 trimethylation (H3K4me3) transcription activation mark. Here we speculate that the increased density of this mark may drive the increased p21 expression observed in the presence of the cp-tiRNA sponge. (b) We observed little effect of the STARD13 sponge on CTCF density, but our results indicate that the sponge nonetheless induces reduced nucleosome density and STARD13 expression. Here we propose that reduced levels or concentrations of H3K4me3 marks due to the decrease in nucleosome density may modulate STARD13 expression. (a, b) Black, green and red text indicates no change, increased levels or decreased levels, respectively.