Linda Rubio Research
The Heat Shock Response is an evolutionarily conserved mechanism that allows eukaryotes to survive stressful environmental conditions. This response is regulated by Hsf1, which activates the transcription of genes encoding molecular chaperones (Heat Shock Proteins, HSP’s) that are needed to overcome proteotoxicity caused by stresses such as heat shock. Accompanying the robust transcriptional activation of HSP genes, Hsf1 dynamically remodels the genome topology of budding yeast (Chowdhary, Kainth, et. al., Mol. Cell. Biol., 2017; Cell Reports, 2019). This remodeling of genome architecture leads to strong intergenic interactions amongst genes upregulated by Hsf1, and both intrachromosomal and interchromosomal contacts have been observed. Such physical interaction is absolutely dependent on exposure of cells to an acute heat shock, as HSP gene coalescence is not observed in non-stressed cells. How Hsf1 induces this dynamic alteration of genome structure is unknown. In an effort to identify some of the molecular players involved, I used fluorescence microscopy combined with live cell analysis of a yeast strain bearing LacO tagged alleles of HSP12 and HSP104, both part of the Hsf1 regulon. This biological system shows great dynamism under heat shock (38°C), as both tagged HSPs coalesce within 2.5 min of heat shock in 30-40% of the population, well above the background levels (<10%) seen in non-heat-shocked cells, allowing us to study this biological process in a live setting.
Filamentous actin (F-actin) has been shown to be involved in chromosomal dynamics in higher eukaryotes, as well as in budding yeast, which makes it an interesting candidate to mediate HSP gene coalescence. In preliminary experiments, I have tested the role of actin by using the inhibitor Latrunculin A (LatA). Pre-treatment of cells with LatA abolished HSP12-HSP104 coalescence in response to heat shock, suggesting a role for actin in Hsf1-mediated genome restructuring. Whether the form of actin mediating coalescence is filamentous or monomeric, and the precise role that it plays, is the focus of my current studies.