Graduate Student Emory University Atlanta, Georgia
Body of Abstract: In flowering plants, histone variant H2A.Z enrichment co-occurs with trimethylation of histone H3 on lysine 27 (H3K27me3) in the bodies of stimulus-inducible genes that are in a transcriptionally repressed state. Intriguingly, proper incorporation of H3K27me3 requires H2A.Z, and deposition of H2A.Z also depends on H3K27me3, suggesting a feedback loop between this variant and the polycomb repressive complex 2 (PRC2). However, a mechanism linking H2A.Z deposition, polycomb activity, and transcriptional repression has yet to be established, due in part to the rapidity of chromatin changes that occur as a stimulus-responsive gene transitions from an active state to a repressed state. The Phosphate Starvation Inducible (PSI) genes offer a unique system to study the order of events that take place during establishment of H2A.Z/H3K27me3-dependent silencing, as the silencing of these genes depends on H2A.Z deposition and repression can be rapidly induced by changing phosphate conditions in the growth media. Thus, we applied Isolation of Nuclei Tagged in specific Cell Types followed by and Cleavage Under Targets and Tagmentation (INTACT-CUT&Tag) to capture chromatin profiles of H2A.Z, H3K27me3, H3K4me3, H2AK119Ub in as few as 50,000 root epidermal hair cell nuclei over several hours as the PSI genes become repressed. Coupled with INTACT-RNA-seq, this approach allows us to follow the order of events, and their dependencies, during establishment of a repressed chromatin state at PSI genes. This time- and cell type-resolved chromatin profiling study will help to reveal the mechanistic link between H2A.Z, polycomb silencing, and repression of stimulus-responsive genes.