549B Poster - 07. Chromatin, epigenetics and genomics
Friday April 08, 2:00 PM - 4:00 PM

Authors:
Kami Ahmad ¹; James Anderson ¹; Steven Henikoff ^1,2

Affiliations:
1) Fred Hutchinson Cancer Research Center; 2) Howard Hughes Medical Institute

Keywords:
g. Polycomb/trithorax complexes; p. other (reprogramming)

Development proceeds by the activation of genes by transcription factors and the inactivation of others by chromatin-mediated gene silencing. In certain cases development can be reversed or redirected by mis-expression of master regulator transcription factors; this reprogramming must involve the activation of new genes and the chromatin-mediated silencing of others. Here, we express the wing-specific Vestigial master regulator to reprogram the developing eye, and test the role of silencing in reprogramming using an H3.3K27M oncohistone mutation that dominantly inhibits histone H3K27 trimethylation. We find that production of the oncohistone blocks eye-to-wing reprogramming. CUT&Tag chromatin profiling of mutant tissues shows that H3K27me3 of domains is generally reduced upon oncohistone production, suggesting that a previous developmental program must be silenced for effective transformation. Strikingly, Vg and H3.3K27M synergize to stimulate overgrowth of eye tissue, a phenotype that resembles that of the oncohistone in human cancers. Transcriptome profiling of elongating RNA Polymerase II implicates the mis-regulation of signaling factors in overgrowth. Our results demonstrate that growth dysregulation can result from the simple combination of crippled silencing and transcription factor mis-expression, an effect that may explain the origins of oncohistone-bearing cancers. We have continued this work to search for additional factors that can synergize with the H3.3K27M oncohistone, and to probe the earliest epigenetic changes in cells as they begin to overproliferate.