PhD Transfer Seminar – Shanelle Mullany (Mitchell Lab)

Enhancers are non-coding sequences that regulate the spatiotemporal expression of target genes. These elements have been found to be fundamental in cell-type specific gene expression and mutations in these regions often leads to disease phenotypes. With such an important role in transcriptional regulation many efforts have been made to annotate enhancers throughout the genome, however these elements are difficult to identify since they reside in the vast non-coding portion of the genome and lack any unique signature. The ENCODE project is dedicated to annotating these elements using genome wide data and predicts these regions primarily through histone modifications that correlate with active enhancers, such as H3K27ac. Functional testing of these predictions however, suggested that less than 30% of these enhancer-annotated sequences have regulatory function. I propose this low accuracy can be improved if we were to understand the true relationship between enhancer activity and the H3K27ac modification. I have investigated H3K27ac at surrounding regions after deletion of nearby active enhancers and determined that active enhancers can initiate H3K27ac at regions within 10-100kb that hold no regulatory capacity. I will first investigate the mechanisms of this chromatin modification spreading. Next, I will insert a variety of synthetic enhancers downstream of a receptive promoter and quantify the subsequent H3K27ac deposits to reveal the relationship between sequence, histone modification and enhancer activity. This analysis should reveal the determinants of H3K27ac enrichment, as well as provide insight into the enhancer sequence code by interrogating the regulatory capacities of various synthetic sequences when integrated into the genome.