Epigenetic mechanisms enhancing transcriptional response to environmental heat stress

Project Summary Living organisms have evolved a universal heat stress or heat shock (HS) response to mitigate the proteotoxic effects of a rise in environmental temperatures. For all eukaryotes, the master regulator of the HS response is the highly conserved, homo-trimeric heat shock transcription factor (HSF1) which activate transcription of the gene family encoding HS proteins (HSPs), molecular chaperones assisting protein folding. Although transactivation by stress-regulated HSF1 is well understood, earlier events in the HSF1 path to transcription remain unclear. This proposal tests the hypothesis that the chromatin architecture of HS promoters is pre-set by distinct TFs such as NFY and SP1 collaborating with ATP-driven chromatin remodelers to establish and maintain, or to ‘pioneer’ open chromatin, thereby enhancing HSF1 binding and enabling a temporally efficient response to the environmental temperature stress. The proposed study applies the emergent technology of live-cell single- molecule tracking (SMT) to directly image endogenous, tagged NFY and SP1 in living cells, allowing quantification of diffusion kinetics at high spatiotemporal resolution and in vivo temporal occupancy as an important Pioneering TF (PTF) parameter and development of new biochemical assays for nucleosome displacement that distinguish between conceptually distinct mechanisms for generating chromatin accessibility. These biochemical assays will provide mechanistic insights on how PTFs and chromatin remodelers collaborate, informing the process by which HS gene chromatin is pre-set to accelerate HSF1 binding to chromatin, and are generally applicable to assess the pioneering potential of other TFs expressed constitutively or are inducible by environmental agents.