The circadian clock regulates many aspects of immunity. Bacterial infections are affected by time of day, but the mechanisms involved remain undefined. Here we show that loss of the core clock ...protein BMAL1 in macrophages confers protection against pneumococcal pneumonia. Infected mice show both reduced weight loss and lower bacterial burden in circulating blood. In vivo studies of macrophage phagocytosis reveal increased bacterial ingestion following Bmal1 deletion, which was also seen in vitro. BMAL1−/− macrophages exhibited marked differences in actin cytoskeletal organization, a phosphoproteome enriched for cytoskeletal changes, with reduced phosphocofilin and increased active RhoA. Further analysis of the BMAL1−/− macrophages identified altered cell morphology and increased motility. Mechanistically, BMAL1 regulated a network of cell movement genes, 148 of which were within 100 kb of high-confidence BMAL1 binding sites. Links to RhoA function were identified, with 29 genes impacting RhoA expression or activation. RhoA inhibition restored the phagocytic phenotype to that seen in control macrophages. In summary, we identify a surprising gain of antibacterial function due to loss of BMAL1 in macrophages, associated with a RhoA-dependent cytoskeletal change, an increase in cell motility, and gain of phagocytic function.
Atomic clocks are highly precise timing devices used in numerous Positioning, Navigation, and Timing (PNT) applications on the ground and in outer space. In recent years, however, more precise timing ...solutions based on optical technology have been introduced as current technology capabilities advance. State-of-the-art optical clocks-predicted to be the next level of their predecessor atomic clocks-have achieved ultimate uncertainty of 1 × 10
and beyond, which exceeds the best atomic clock's performance by two orders of magnitude. Hence, the successful development of optical clocks has drawn significant attention in academia and industry to exploit many more opportunities. This paper first provides an overview of the emerging optical clock technology, its current development, and characteristics, followed by a clock stability analysis of some of the successfully developed optical clocks against current Global Navigation Satellite System (GNSS) satellite clocks to discuss the optical clock potentiality in GNSS positioning. The overlapping Allan Deviation (ADEV) method is applied to estimate the satellite clock stability from International GNSS Service (IGS) clock products, whereas the optical clock details are sourced from the existing literature. The findings are (a) the optical clocks are more stable than that of atomic clocks onboard GNSS satellites, though they may require further technological maturity to meet spacecraft payload requirements, and (b) in GNSS positioning, optical clocks could potentially offer less than a 1 mm range error (clock-related) in 30 s and at least 10 times better timing performance after 900 s in contrast to the Galileo satellite atomic clocks-which is determined in this study as the most stable GNSS atomic clock type used in satellite positioning.
The mammalian circadian clock has evolved as an adaptation to the 24-h light/darkness cycle on earth. Maintaining cellular activities in synchrony with the activities of the organism (such as eating ...and sleeping) helps different tissue and organ systems coordinate and optimize their performance. The full extent of the mechanisms by which cells maintain the clock are still under investigation, but involve a core set of clock genes that regulate large networks of gene transcription both by direct transcriptional activation/repression as well as the recruitment of proteins that modify chromatin states more broadly.
Dendritic cells play a key role in processing and presenting antigens to naïve T cells to prime adaptive immunity. Circadian rhythms are known to regulate many aspects of immunity; however, the role ...of circadian rhythms in dendritic cell function is still unclear. Here, we show greater T cell responses when mice are immunised in the middle of their rest versus their active phase. We find a circadian rhythm in antigen processing that correlates with rhythms in both mitochondrial morphology and metabolism, dependent on the molecular clock gene, Bmal1. Using Mdivi-1, a compound that promotes mitochondrial fusion, we are able to rescue the circadian deficit in antigen processing and mechanistically link mitochondrial morphology and antigen processing. Furthermore, we find that circadian changes in mitochondrial Ca
are central to the circadian regulation of antigen processing. Our results indicate that rhythmic changes in mitochondrial calcium, which are associated with changes in mitochondrial morphology, regulate antigen processing.
Liquid-liquid phase separation (LLPS) underlies diverse biological processes. Because most LLPS studies were performed in vitro using recombinant proteins or in cells that overexpress protein, the ...physiological relevance of LLPS for endogenous protein is often unclear. PERIOD, the intrinsically disordered domain-rich proteins, are central mammalian circadian clock components and interact with other clock proteins in the core circadian negative feedback loop. Different core clock proteins were previously shown to form large complexes. Circadian clock studies often rely on experiments that overexpress clock proteins. Here, we show that when Per2 transgene was stably expressed in cells, PER2 protein formed nuclear phosphorylation-dependent slow-moving LLPS condensates that recruited other clock proteins. Super-resolution microscopy of endogenous PER2, however, revealed formation of circadian-controlled, rapidly diffusing nuclear microbodies that were resistant to protein concentration changes, hexanediol treatment, and loss of phosphorylation, indicating that they are distinct from the LLPS condensates caused by protein overexpression. Surprisingly, only a small fraction of endogenous PER2 microbodies transiently interact with endogenous BMAL1 and CRY1, a conclusion that was confirmed in cells and in mice tissues, suggesting an enzyme-like mechanism in the circadian negative feedback process. Together, these results demonstrate that the dynamic interactions of core clock proteins are a key feature of mammalian circadian clock mechanism and the importance of examining endogenous proteins in LLPS and circadian clock studies.
Marine organisms track multiple environmental cycles with dedicated biological clocks and thus show remarkably plastic molecular and behavioral rhythms.The combination of new marine model organisms ...and genome-engineering technologies are advancing our understanding of the molecular mechanisms underlying circatidal and circalunar rhythms.Brain and muscle Arnt-like protein-1 (BMAL1) is a molecular link between the circadian (24 h) and circatidal (12.4 h) clocks, while PERIOD and CRYPTOCHROME 2 appear to be specific to circadian rhythms.Specific opsin and cryptochrome photoreceptors allow organisms to recognize moonlight and adjust their rhythmic behavior accordingly.
The coastline is a particularly challenging environment for its inhabitants. Not only do they have to cope with the solar day and the passing of seasons, but they must also deal with tides. In addition, many marine species track the phase of the moon, especially to coordinate reproduction. Marine animals show remarkable behavioral and physiological adaptability, using biological clocks to anticipate specific environmental cycles. Presently, we lack a basic understanding of the molecular mechanisms underlying circatidal and circalunar clocks. Recent advances in genome engineering and the development of genetically tractable marine model organisms are transforming how we study these timekeeping mechanisms and opening a novel era in marine chronobiology.
The coastline is a particularly challenging environment for its inhabitants. Not only do they have to cope with the solar day and the passing of seasons, but they must also deal with tides. In addition, many marine species track the phase of the moon, especially to coordinate reproduction. Marine animals show remarkable behavioral and physiological adaptability, using biological clocks to anticipate specific environmental cycles. Presently, we lack a basic understanding of the molecular mechanisms underlying circatidal and circalunar clocks. Recent advances in genome engineering and the development of genetically tractable marine model organisms are transforming how we study these timekeeping mechanisms and opening a novel era in marine chronobiology.
Circadian clocks regulate numerous physiological processes that vary across the day-night (diurnal) cycle, but if and how the circadian clock regulates the adaptive immune system is mostly unclear. ...lnterleukin-17–producing CD4⁺ T helper (T H 17) cells are proinflammatory immune cells that protect against bacterial and fungal infections at mucosal surfaces. Their lineage specification is regulated by the orphan nuclear receptor RORγt We show that the transcription factor NFIL3 suppresses T H 17 cell development by directly binding and repressing the Rorγt promoter. NFIL3 links T H 17 cell development to the circadian clock network through the transcription factor REV-ERBα. Accordingly, T H 17 lineage specification varies diurnally and is altered in Rev-erbα- ⁻ - mice. Light-cycle disruption elevated intestinal T H 17 cell frequencies and increased susceptibility to inflammatory disease. Thus, lineage specification of a key immune cell is under direct circadian control.
The transcriptional repressions driven by the circadian core clock repressors RevErbα, E4BP4, and CRY1/PER1 involve feedback loops which are mandatory for generating the circadian rhythms. These ...repressors are known to bind to cognate DNA binding sites, but how their circadian bindings trigger the cascade of events leading to these repressions remain to be elucidated. Through molecular and genetic analyses, we now demonstrate that the chromatin protein HP1α plays a key role in these transcriptional repressions of both the circadian clock (CC) genes and their cognate output genes (CCGs). We show that these CC repressors recruit the HP1α protein downstream from a repressive cascade, and that this recruitment is mandatory for the maintenance of both the CC integrity and the expression of the circadian genes. We further show that the presence of HP1α is critical for both the repressor-induced chromatin compaction and the generation of "transcriptionally repressed biomolecular hydrophobic condensates" and demonstrates that HP1α is mandatory within the CC output genes for both the recruitment of DNA methylating enzymes on the intronic deoxyCpG islands and their subsequent methylation.
The mammalian circadian clock relies on the transcription factor CLOCK:BMAL1 to coordinate the rhythmic expression of 15% of the transcriptome and control the daily regulation of biological ...functions. The recent characterization of CLOCK:BMAL1 cistrome revealed that although CLOCK:BMAL1 binds synchronously to all of its target genes, its transcriptional output is highly heterogeneous. By performing a meta-analysis of several independent genome-wide datasets, we found that the binding of other transcription factors at CLOCK:BMAL1 enhancers likely contribute to the heterogeneity of CLOCK:BMAL1 transcriptional output. While CLOCK:BMAL1 rhythmic DNA binding promotes rhythmic nucleosome removal, it is not sufficient to generate transcriptionally active enhancers as assessed by H3K27ac signal, RNA Polymerase II recruitment, and eRNA expression. Instead, the transcriptional activity of CLOCK:BMAL1 enhancers appears to rely on the activity of ubiquitously expressed transcription factors, and not tissue-specific transcription factors, recruited at nearby binding sites. The contribution of other transcription factors is exemplified by how fasting, which effects several transcription factors but not CLOCK:BMAL1, either decreases or increases the amplitude of many rhythmically expressed CLOCK:BMAL1 target genes. Together, our analysis suggests that CLOCK:BMAL1 promotes a transcriptionally permissive chromatin landscape that primes its target genes for transcription activation rather than directly activating transcription, and provides a new framework to explain how environmental or pathological conditions can reprogram the rhythmic expression of clock-controlled genes.
Singly ionized ytterbium, with ultranarrow optical clock transitions at 467 and 436 nm, is a convenient system for the realization of optical atomic clocks and tests of present-day variation of ...fundamental constants. We present the first direct measurement of the frequency ratio of these two clock transitions, without reference to a cesium primary standard, and using the same single ion of Yb+171. The absolute frequencies of both transitions are also presented, each with a relative standard uncertainty of 6x10-16. Combining our results with those from other experiments, we report a threefold improvement in the constraint on the time variation of the proton-to-electron mass ratio, mu super(.)/ mu =0.2(1.1)x10-16 yr-1, along with an improved constraint on time variation of the fine structure constant, alpha super(.)/ alpha =-0.7(2.1)x10-17 yr-1
PDF
