Bacterial variability in the mammalian gut captured by a single-cell synthetic oscillator

Synthetic gene oscillators have the potential to control timed functions and periodic gene expression in engineered cells. Such oscillators have been refined in bacteria in vitro, however, these systems have lacked the robustness and precision necessary for applications in complex in vivo environments, such as the mammalian gut. Here, we demonstrate the implementation of a synthetic oscillator capable of keeping robust time in the mouse gut over periods of days. The oscillations provide a marker of bacterial growth at a single-cell level enabling quantification of bacterial dynamics in response to inflammation and underlying variations in the gut microbiota. Our work directly detects increased bacterial growth heterogeneity during disease and differences between spatial niches in the gut, demonstrating the deployment of a precise engineered genetic oscillator in real-life settings.

Rhythmic chromatin interactions with lamin B1 reflect stochasticity in variable lamina-associated domains during the circadian cycle

Many mammalian genes exhibit circadian expression patterns concordant with periodic binding of transcription factors, chromatin modifications and chromosomal interactions. Here, we report periodic interactions of chromatin with nuclear lamins, suggesting rhythmic associations with the nuclear lamina. Entrainment of the circadian clock is accompanied in mouse liver by a gain of lamin B1-chromatin interactions, followed by oscillations in these interactions at hundreds of lamina-associated domains (LADs). A subset of these oscillations exhibit distinct 12, 18, 24 or 30-h periodicity in our dataset, and affect one or both LAD borders or entire stand-alone LADs. However, most LADs are conserved during the circadian cycle, and periodic LADs are seldom occurrences rather than dominant features of variable LADs. Periodic LADs display oscillation asynchrony between 5’ and 3’ LAD borders, and are uncoupled from periodic gene expression within or in vicinity of these LADs. Accordingly, periodic genes, including central clock-control genes, are often located megabases away from LADs, suggesting residence in a transcriptionally permissive environment throughout the circadian cycle. Autonomous oscillatory associations of the genome with nuclear lamins provide new evidence for rhythmic spatial chromatin configurations. Nevertheless, our data suggest that periodic LADs reflect stochasticity in lamin-chromatin interactions underlying chromatin dynamics in the liver during the circadian cycle. They also argue that periodic gene expression is by and large not regulated by rhythmic chromatin associations with the nuclear lamina.

INO80 Chromatin Remodelling Coordinates Metabolic Homeostasis with Cell Division

ABSTRACTAdaptive survival requires the coordination of nutrient availability with expenditure of cellular resources. For example, in nutrient-limited environments, 50% of all S. cerevisiae genes synchronize and exhibit periodic bursts of expression in coordination with respiration and cell division in the Yeast Metabolic Cycle (YMC). Despite the importance of metabolic and proliferative synchrony, the majority of YMC regulators are currently unknown. Here we demonstrate that the INO80 chromatin-remodelling complex is required to coordinate respiration and cell division with periodic gene expression. Specifically, INO80 mutants have severe defects in oxygen consumption and promiscuous cell division that is no longer coupled with metabolic status. In mutant cells, chromatin accessibility of periodic genes, including TORC-responsive genes, is relatively static, concomitant with severely attenuated gene expression. Collectively, these results reveal that the INO80 complex mediates metabolic signaling to chromatin in order to restrict proliferation to metabolically optimal states.

Live-cell monitoring of periodic gene expression in synchronous human cells identifies Forkhead genes involved in cell cycle control

We developed a system to monitor periodic luciferase activity from cell cycle–regulated promoters in synchronous cells. Reporters were driven by a minimal human E2F1 promoter with peak expression in G1/S or a basal promoter with six Forkhead DNA-binding sites with peak expression at G2/M. After cell cycle synchronization, luciferase activity was measured in live cells at 10-min intervals across three to four synchronous cell cycles, allowing unprecedented resolution of cell cycle–regulated gene expression. We used this assay to screen Forkhead transcription factors for control of periodic gene expression. We confirmed a role for FOXM1 and identified two novel cell cycle regulators, FOXJ3 and FOXK1. Knockdown of FOXJ3 and FOXK1 eliminated cell cycle–dependent oscillations and resulted in decreased cell proliferation rates. Analysis of genes regulated by FOXJ3 and FOXK1 showed that FOXJ3 may regulate a network of zinc finger proteins and that FOXK1 binds to the promoter and regulates DHFR, TYMS, GSDMD, and the E2F binding partner TFDP1. Chromatin immunoprecipitation followed by high-throughput sequencing analysis identified 4329 genomic loci bound by FOXK1, 83% of which contained a FOXK1-binding motif. We verified that a subset of these loci are activated by wild-type FOXK1 but not by a FOXK1 (H355A) DNA-binding mutant.