Use of firefly luciferase activity assays to monitor circadian molecular rhythms in vivo and in vitro

Methods to Monitor Circadian Clock Function in Skeletal Muscle

The circadian clock exerts temporal regulation in physiology and behavior. The skeletal muscle possesses cell-autonomous clock circuits that play key roles in diverse tissue growth, remodeling, and metabolic processes. Recent advances reveal the intrinsic properties, molecular regulations, and physiological functions of the molecular clock oscillators in progenitor and mature myocytes in muscle. While various approaches have been applied to examine clock functions in tissue explants or cell culture systems, defining the tissue-intrinsic circadian clock in muscle requires sensitive real-time monitoring using a Period2 promoter-driven luciferase reporter knock-in mouse model. This chapter describes the gold standard of applying the Per2::Luc reporter line to assess clock properties in skeletal muscle. This technique is suitable for the analysis of clock function in ex vivo muscle preps using intact muscle groups, dissected muscle strips, and cell culture systems using primary myoblasts or myotubes.

Generation of Mouse Primary Hypothalamic Neuronal Cultures for Circadian Bioluminescence Assays

An endogenous circadian clock system enables organisms to adapt to time-of-day dependent environmental changes. In consequence, most physiological processes exhibit daily rhythms of, e.g., energy metabolism, immune function, sleep, or hormone production. Hypothalamic circadian clocks have been identified to play a particular role in coordinating many of these processes. Primary neuronal cultures are widely used as a physiologically relevant model to study molecular events within neurons. However, as circadian rhythms include dynamic molecular changes over longer timescales that vary between individual cells, longitudinal measurement methods are essential to investigate the regulation of circadian clocks of hypothalamic neurons. Here we provide a protocol for generating primary hypothalamic neuronal cultures expressing a circadian luciferase reporter. Such reporter cells can be used to longitudinally monitor cellular circadian rhythms at high temporal resolution by performing bioluminescence measurements.

On the move through time - a historical review of plant clock research

The circadian clock is an important regulator of growth and development that has evolved to help organisms to anticipate the predictably occurring events on the planet, such as light-dark transitions, and adapt growth and development to these. This review looks back in history on how knowledge about the endogenous biological clock has been acquired over the centuries, with a focus on discoveries in plants. Key findings at the physiological, genetic and molecular level are described and the role of the circadian clock in important molecular processes is reviewed.

Flexible Measurement of Bioluminescent Reporters Using an Automated Longitudinal Luciferase Imaging Gas- and Temperature-optimized Recorder (ALLIGATOR)

Luciferase-based reporters of cellular gene expression are in widespread use for both longitudinal and end-point assays of biological activity. In circadian rhythms research, for example, clock gene fusions with firefly luciferase give rise to robust rhythms in cellular bioluminescence that persist over many days. Technical limitations associated with photomultiplier tubes (PMT) or conventional microscopy-based methods for bioluminescence quantification have typically demanded that cells and tissues be maintained under quite non-physiological conditions during recording, with a trade-off between sensitivity and throughput. Here, we report a refinement of prior methods that allows long-term bioluminescence imaging with high sensitivity and throughput which supports a broad range of culture conditions, including variable gas and humidity control, and that accepts many different tissue culture plates and dishes. This automated longitudinal luciferase imaging gas- and temperature-optimized recorder (ALLIGATOR) also allows the observation of spatial variations in luciferase expression across a cell monolayer or tissue, which cannot readily be observed by traditional methods. We highlight how the ALLIGATOR provides vastly increased flexibility for the detection of luciferase activity when compared with existing methods.

Multiscale adaptive analysis of circadian rhythms and intradaily variability: Application to actigraphy time series in acute insomnia subjects

Circadian rhythms become less dominant and less regular with chronic-degenerative disease, such that to accurately assess these pathological conditions it is important to quantify not only periodic characteristics but also more irregular aspects of the corresponding time series. Novel data-adaptive techniques, such as singular spectrum analysis (SSA), allow for the decomposition of experimental time series, in a model-free way, into a trend, quasiperiodic components and noise fluctuations. We compared SSA with the traditional techniques of cosinor analysis and intradaily variability using 1-week continuous actigraphy data in young adults with acute insomnia and healthy age-matched controls. The findings suggest a small but significant delay in circadian components in the subjects with acute insomnia, i.e. a larger acrophase, and alterations in the day-to-day variability of acrophase and amplitude. The power of the ultradian components follows a fractal 1/f power law for controls, whereas for those with acute insomnia this power law breaks down because of an increased variability at the 90min time scale, reminiscent of Kleitman’s basic rest-activity (BRAC) cycles. This suggests that for healthy sleepers attention and activity can be sustained at whatever time scale required by circumstances, whereas for those with acute insomnia this capacity may be impaired and these individuals need to rest or switch activities in order to stay focused. Traditional methods of circadian rhythm analysis are unable to detect the more subtle effects of day-to-day variability and ultradian rhythm fragmentation at the specific 90min time scale.

Circadian rhythms identified in Caenorhabditis elegans by in vivo long-term monitoring of a bioluminescent reporter

Circadian rhythms are based on endogenous clocks that allow organisms to adjust their physiology and behavior by entrainment to the solar day and, in turn, to select the optimal times for most biological variables. Diverse model systems-including mice, flies, fungi, plants, and bacteria-have provided important insights into the mechanisms of circadian rhythmicity. However, the general principles that govern the circadian clock of Caenorhabditis elegans have remained largely elusive. Here we report robust molecular circadian rhythms in C elegans recorded with a bioluminescence assay in vivo and demonstrate the main features of the circadian system of the nematode. By constructing a luciferase-based reporter coupled to the promoter of the suppressor of activated let-60 Ras (sur-5) gene, we show in both population and single-nematode assays that C elegans expresses ∼24-h rhythms that can be entrained by light/dark and temperature cycles. We provide evidence that these rhythms are temperature-compensated and can be re-entrained after phase changes of the synchronizing agents. In addition, we demonstrate that light and temperature sensing requires the photoreceptors LITE and GUR-3, and the cyclic nucleotide-gated channel subunit TAX-2. Our results shed light on C elegans circadian biology and demonstrate evolutionarily conserved features in the circadian system of the nematode.

Automated monitoring and quantitative analysis of feeding behaviour in Drosophila

Food ingestion is one of the defining behaviours of all animals, but its quantification and analysis remain challenging. This is especially the case for feeding behaviour in small, genetically tractable animals such as Drosophila melanogaster. Here, we present a method based on capacitive measurements, which allows the detailed, automated and high-throughput quantification of feeding behaviour. Using this method, we were able to measure the volume ingested in single sips of an individual, and monitor the absorption of food with high temporal resolution. We demonstrate that flies ingest food by rhythmically extending their proboscis with a frequency that is not modulated by the internal state of the animal. Instead, hunger and satiety homeostatically modulate the microstructure of feeding. These results highlight similarities of food intake regulation between insects, rodents, and humans, pointing to a common strategy in how the nervous systems of different animals control food intake.

Feeding is an important behaviour, but its quantification remains challenging, particularly in small animal models like Drosophila melanogaster. Here the authors describe a method which uses capacitive sensing for automated high-resolution measuring of feeding behaviour in individual flies.

In vivo bioluminescence imaging monitoring of stem cells' participation in choroidal neovascularization

BACKGROUND

Choroidal neovascularization (CNV) is common in various retinal diseases and is one of the most common causes of severe and irreversible visual loss. Our previous works suggested that bone marrow-derived cells (BMCs) participate in CNV, but little is known about stem cells' dynamic change when injected into mouse CNV. In vivo optical bioluminescence imaging (BLI) is a newly developing technology for dynamically observing biological behavior. Using this technology, we can observe the stem cells' dynamic behavior in CNV, in vivo.

METHODS

Two types of BMCs were used: bone marrow mononuclear cells (BMMNCs) and bone mesenchymal stem cells (MSCs). Cells were characterized using flow cytometry and BLI. C57BL/6J mice (n = 6/group) underwent CNV followed by caudal vein injection of 4 × 10⁶ BMMNCs, MSCs or phosphate buffer. Cell survival was measured: (1) in vivo using BLI during 2 weeks, and (2) in vitro using firefly luciferase (Fluc) assays and histology.

RESULTS

BMMNCs and MSCs expressed a similar Fluc reporter enzyme, as confirmed by luminometry. After injection into CNV mouse models, the two cell types showed dynamic behavior in CNV using BLI. The in vitro Fluc assay and histology results provided further proof for the above results.

CONCLUSION

This is the first study comparing the behavior of stem cells in CNV using BLI, in vivo. BMMNCs and MSCs could contribute to CNV and could serve as delivery vehicles for CNV treatments. Meanwhile, BLI could lay a foundation for CNV mechanism research in a prospective manner.

It's time to swim! Zebrafish and the circadian clock

The zebrafish represents a fascinating model for studying key aspects of the vertebrate circadian timing system. Easy access to early embryonic development has made this species ideal for investigating how the clock is first established during embryogenesis. In particular, the molecular basis for the functional development of the zebrafish pineal gland has received much attention. In addition to this dedicated clock and photoreceptor organ, and unlike the situation in mammals, the clocks in zebrafish peripheral tissues and even cell lines are entrainable by direct exposure to light thus providing unique insight into the function and evolution of the light input pathway. Finally, the small size, low maintenance costs and high fecundity of this fish together with the availability of genetic tools make this an attractive model for forward genetic analysis of the circadian clock. Here, we review the work that has established the zebrafish as a valuable clock model organism and highlight the key questions that will shape the future direction of research.

Fluorescence/luminescence circadian imaging of complex tissues at single-cell resolution

The use of luciferase reporter genes together with luminescence detection has enabled high frequency monitoring of molecular circadian clock function in living tissues. With the help of an intensified CCD camera combined with an inverted epifluorescence microscope, the authors have established a new imaging strategy that makes use of transgenic cell type-specific expression of fluorescent proteins to identify cells of interest for subsequent circadian luminescence recording at single-cell resolution.

Simultaneous tracking of fly movement and gene expression using GFP

Background

Green Fluorescent Protein (GFP) is used extensively as a reporter for transgene expression in Drosophila and other organisms. However, GFP has not generally been used as a reporter for circadian patterns of gene expression, and it has not previously been possible to correlate patterns of reporter expression with 3D movement and behavior of transgenic animals.

Results

We present a video tracking system that allows tissue-specific GFP expression to be quantified and correlated with 3D animal movement in real time. eyeless/Pax6 reporter expression had a 12 hr period that correlated with fly activity levels.

hsp70 and hsp22 gene reporters were induced during fly aging in circadian patterns (24 hr and 18 hr periods, respectively), and spiked in the hours preceding and overlapping the death of the animal. The phase of hsp gene reporter expression relative to fly activity levels was different for each fly, and remained the same throughout the life span.

Conclusion

These experiments demonstrate that GFP can readily be used to assay longitudinally fly movement and tissue-specific patterns of gene expression. The hsp22-GFP and hsp70-GFP expression patterns were found to reflect accurately the endogenous gene expression patterns, including induction during aging and circadian periodicity. The combination of these new tracking methods with the hsp-GFP reporters revealed additional information, including a spike in hsp22 and hsp70 reporter expression preceding death, and an intriguing fly-to-fly variability in the phase of hsp70 and hsp22 reporter expression patterns. These methods allow specific temporal patterns of gene expression to be correlated with temporal patterns of animal activity, behavior and mortality.