OR33-02 The Effects Of Timing And Patterns Of Hormone Stimulation On Single Molecule Dynamics And Gene Regulation In Vivo

Disclosure: D.A. Stavreva: None. L. Hoang: None. K. Wagh: None. R. Chari: None. A. Upadhyaya: None. G.L. Hager: None. Even though most studies on hormonal signaling are performed under continuous stimulation, secretion of many hormones follows a circadian pattern, comprised of periodic (ultradian) pulses with short duration. Using glucocorticoid receptor (GR) signaling as a model system we have previously demonstrated that receptor occupancy of regulatory elements precisely tracks the hormonal pulses resulting in cyclic GR-mediated transcription (gene pulsing) (Stavreva et al., NCB 2009). Using various genomic approaches, we have also uncovered the impact of ultradian and constant stimulation on the lifetimes of chromatin accessibility and long-range promoter/enhancer interactions (Stavreva et al., Genome Res. 2015). By visualizing RNA synthesis from single-copy GR-regulated transcription sites (TSs) we demonstrated treatment-specific RNA bursting patterns. Moreover, our single molecule tracking (SMT) experiments showed that transcription factor (TF) dynamics determine burst duration and frequency (Stavreva et al., 2019). To further study the in vivo dynamics of various TFs we tagged the endogenous GR as well as the estrogen, progesterone receptor (ER and PR, respectively), and the large Pol II subunit (Rpb1) with Halo tag in MCF7 cells. We use SMT in combination with other microscopy and biochemical approaches to i) map the dynamics of TFs in response to constant and ultradian hormone stimulations, and ii) determine their effects on transcription regulation. These studies will help us better understand the importance of timing and pattern of hormone treatment for proper gene regulation in different physiological contexts. Presentation: Sunday, June 18, 2023