The human intestinal enteroids were obtained from the lab of Dr. Michael Helmrath at Cincinnati Children&#39;s Hospital Medical Center (CCHMC). This work was supported by R01 DK11005 (CIH) and the University of Cincinnati Cancer Center Pilot Funding. We are grateful for imaging support from the University of Cincinnati Live Microscopy Core (NIH S10OD030402).

All experiments using human tissues for the generation of HIEs were approved by an IRB at CCHMC (IRB#2014-0427). See the Table of Materials for details related to all materials used in this protocol.
NOTE: To illustrate the procedure outlined in this protocol, we utilized Bmal1-luc human intestinal enteroids (HIEs). These enteroids underwent stable lentiviral transduction22 with the pABpuro-BluF reporter plasmid, which contains the Bmal1 promoter fused to luciferase, showing the activity of the Bmal1 promoter21.
1. Lentiviral transduction
<ol>
	<li>Carry out the lentiviral transduction22 under stem cell-enriched conditions for HIEs. Specifically, ensure the formation of spheroids in HIEs within 3-4 days after passage in the intestinal growth media, which creates stem cell-enriched conditions.</li>
	<li>After the lentiviral transduction22, carry out antibiotic selection with 2 &#181;g/mL puromycin, recover the puromycin-resistant HIEs, and passage them with relatively high density (i.e., 1 well into 2 wells) for 2-3x. If the growth rate of the HIEs is slow, add 10 &#181;M ROCK inhibitors (Y-27632) and 10 &#181;M GSK-3 inhibitor (CHIR-99021) to the intestinal organoid growth medium.</li>
</ol>
2. Preparation of organoids for bioluminescence assay
<ol>
	<li>Day 1: Passage HIEs to 35 mm round dishes.
	<ol>
		<li>Briefly, for expansion of HIEs, mix the HIEs with growth factor-reduced (GFR) 3D culture matrix and seed them onto 24-well plates with three droplets of 10 &#181;L of 3D culture matrix per well. Add 350 &#181;L of the HIE growth medium and change it every other day. 
		NOTE: The density of HIE in the 3D culture matrix is critical for the growth of enteroids. Approximately, the number of spheroids should exceed more than 50 in each droplet. If the number is low, the growth rate of the HIE is negatively affected.</li>
		<li>When HIEs grow sufficiently (approximately 7 days after the post-passage), collect HIEs from four wells into 1.5 mL microcentrifuge tubes.</li>
		<li>Wash the HIEs with the cold PBS using a benchtop mini centrifuge (2,000 &#215; g) for 40 s quick spin to remove debris and excessive 3D culture matrix by pipet.</li>
		<li>Add 0.5 mL of the cold PBS into the pellet and apply physical turbulence by syringing up to 10x with a 1 mL insulin syringe to dissociate the HIEs.</li>
		<li>Spin down the dissociated HIEs with a benchtop mini centrifuge as in step 2.1.3 and gently remove the supernatant by pipet. Then, place the microcentrifuge tube with the HIE pellet on ice to cool down for approximately 3 min.</li>
		<li>Add GFR 3D culture matrix to the microcentrifuge tube and mix it with the HIE pellet. 
		NOTE: Calculate the amount of the 3D culture matrix based on the number of 35 mm round dishes that will be used for the experiment. We generally seed 30 &#181;L of 3D culture matrix droplets per round dish.</li>
		<li>Seed the mixture of HIEs and the 3D culture matrix on the center of the 35 mm round dish and incubate the dish at 37 &#176;C for 20 min to solidify the 3D culture matrix. 
		NOTE: The density of seeding HIEs should be determined experimentally. Based on the intensity of bioluminescence, one can determine the number of HIEs during this process.</li>
		<li>Add 2 mL of prewarmed intestinal organoid growth medium to each dish and incubate the dishes in a CO2 incubator until the next step.</li>
	</ol>
	</li>
	<li>Day 3: Initiation of differentiation
	<ol>
		<li>To initiate differentiation of the HIEs, remove the growth medium and add 2 mL of prewarmed differentiation medium. 
		NOTE: See Table 1 for the recipes of the HIE differentiation media23.</li>
	</ol>
	</li>
	<li>Day 4: No additional process is required.</li>
	<li>Day 5: Replace the medium of the enteroids with 2 mL of prewarmed differentiation medium.</li>
	<li>Day 6: Clock synchronization and recording bioluminescence
	<ol>
		<li>To synchronize the molecular clock of enteroids, add 2 &#181;L of 100 &#181;M dexamethasone (Dex) to make the final concentration 100 nM in each dish and then incubate the dishes in a CO2 incubator (37 &#176;C, 5% CO2) for 1 h24.</li>
		<li>During the Dex resetting, prepare the incubating luminometer. Check the CO2 and temperature of the incubating luminometer and set to 5% and 37 &#176;C, respectively. 
		NOTE: It is suggested to wipe the inside of the incubating luminometer with 70% alcohol before and after every use of the machine to keep it sterile.</li>
		<li>After the clock synchronization, replenish the enteroids with 3 mL of prewarmed differentiation medium containing 200 &#181;M D-luciferin. 
		NOTE: As luciferin is light-sensitive, the luciferin-containing medium should be wrapped with foil and prewarmed in a 37 &#176;C heat bath before applying it to the dish.</li>
		<li>Place the dishes in an 8-well dish table of the incubating luminometer and cover the sample dish table with its lid. Place two humidifier chambers with wet tissue or sponge on the top of the sample dish table. This is one-time process. 
		NOTE: After the experiment is started, the lid of the incubating luminometer should be kept closed until the experiment is terminated. Make sure to wet the tissues/sponges enough.</li>
		<li>Close the lid of the machine and initiate the program to measure bioluminescence for the desired number of days and resolution.
		<ol>
			<li>On the software, select the condition settings by clicking the Condition tab and adjust the settings on this panel: number of dishes, measurement time, background processing, and filter type. 
			NOTE: For this demonstration, we selected all dishes from A to H; default measurement time, which is determined by the software based on the number of dishes; waiting time for background processing, and filter type F0. Since there are three filter options, three luminescent colors can be measured simultaneously.</li>
			<li>After entering all suitable settings based on the experiment, save the settings by clicking OK.</li>
			<li>To start running the experiment, click the Run tab | Start button (green triangle icon). Observe the data as raw, noise filtered, or detrended by making appropriate selections on the top of the screen of the software while running experiments. Click on Raw, Noise Filtered, or Detrended tabs to observe the selected data.</li>
			<li>Observe signals for up to 5 days. 
			NOTE: After 5 days of monitoring in an incubating luminometer, enteroids may begin to die due to media depletion. To prevent any possible circadian disruption during the experiment, we do not perform media change for the duration of the experiment.</li>
			<li>At the end of the experiment, stop the run by clicking the Stop button (blue square icon), go to the File tab, and click Save as. Save the data in the Kronos format; export the data to a spreadsheet in the File section by clicking the File option and then selecting Export as excel format under the File for further analysis.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>

Optimizing Human Intestinal Enteroids for Circadian Rhythm Studies

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The authors declare that they have no conflicts of interest.

Bioluminescence assay offers several advantages for the investigation of circadian rhythms, which requires data collection from long-term time course experiments. First, it enables researchers to monitor the gene expression or protein of interest as cells move and proliferate. Without making unnecessary adjustments or disrupting the cells&#39; functions, interested cellular events or gene expression can be recorded using bioluminescence readout, which gives reliable real-time data. Importantly, the bioluminescence assay ...

Circadian clock 
All organisms, from bacteria to mammals, have a complex and dynamic relationship with their environment. Within this relationship, adaptation to environmental changes is critical for the survival of organisms. Most organisms possess circadian rhythms that enable them to adapt and optimize their functions to diurnal cycles of approximately 24 h. The circadian clock is a hierarchical network of central and peripheral clocks that work in cooperation to maintain physiological homeostasis and keep organisms synchronized with daily changes1,2. In mammals, the central or master clock located in the suprachiasmatic nucleus (SCN) receives external cues, such as light, and transmits the information to the peripheral clocks via an advanced interplay of neural and humoral signaling pathways3. In addition to the central clock, peripheral tissues possess their own cell-autonomous circadian clock mechanism, maintained by a transcriptional-translational negative feedback loop (TTFL) regulating tissue-specific clock-controlled genes (CCGs)4,5. This molecular machinery produces approximately 24 h rhythmicity in cellular and physiological events, such as gene expressions, signaling pathways, immune responses, and digestion. The circadian clock is present in almost all mammalian cells, and it has been demonstrated that up to 50% of the genes&#39; expression patterns exhibit circadian rhythmicity6. Considering the abundance of CCGs, disruption of this clock mechanism may result in critical physiological problems. Hence, investigations into circadian rhythms are necessary to elucidate essential biological mechanisms and develop novel therapeutic strategies.
Luciferase reporter system 
In circadian studies, real-time monitoring is critical for a better understanding of cellular behaviors and responses because it allows tracking of temporal changes in gene expression and/or protein levels, providing insights into the molecular mechanisms regulated by the circadian clock. Furthermore, real-time monitoring enables researchers to study the effects of environmental changes on molecular mechanisms7,8. There are numerous techniques for real-time monitoring studies, including bioluminescence assay, which is widely used to track gene expression or protein levels over time. Bioluminescence assay is a method to detect biological processes using light production as a readout. In this assay, an oxidative enzyme that produces bioluminescence (e.g., luciferase) is either transiently or stably transfected into cells of interest, and the bioluminescence readout is measured in the presence of a substrate (e.g., luciferin) over time. For example, the luciferase enzyme produces bioluminescence by oxidizing the substrate luciferin in the presence of ATP9. Due to its short half-life, 3-4 h10, firefly luciferase is a powerful tool for circadian studies in terms of providing real-time dynamic monitoring with minimal background noise11,12,13. For the insertion of DNA with a luciferase-tagged promoter or open reading frame (ORF), the lentiviral gene delivery system is a reliable method that provides high transduction efficacy, stable integration, and low immunogenicity. Stable transduction of a bioluminescent reporter provides robust expression in dividing and non-dividing cells, generating consistent data for circadian studies14.
Organoid as a model 
Traditional immortalized two-dimensional cell lines have been instrumental in biological studies ranging from uncovering fundamental molecular mechanisms of circadian rhythms to drug screening. Despite the convenience of utilizing homogenized cell lines, they lack multicellular structures and intercellular interactions. In contrast, organoids are in vitro 3D multicellular &#34;organ-like&#34; structures that mimic organ structure in a dish by displaying similarity to in vivo tissue architecture and multicellularity, including stem, progenitor, and differentiated cell types15,16. Possessing self-organization, multicellularity, and functionality features makes organoids a remarkable in vitro model representing the cellular and physiological processes occurring in real tissues17. Different types of organoids can be derived from pluripotent stem cells via directed differentiation or adult stem cells harvested from various organs, including the small intestine, brain, liver, lung, and kidney18,19. Since organoid structures possess a real tissue-like architecture and function with multicellularity and dynamic cell-to-cell interaction, they are superior to homogenized cell lines for understanding the cellular events occurring in in vivo tissues. Organoids are also easily manipulated and can be grown under controlled conditions, making them useful for circadian studies20.
The main purpose of this work is to introduce a real-time monitoring method utilizing a bioluminescence assay specifically tailored for studying circadian rhythms in multicellular 3D organoids. Real-time monitoring of cellular events using a bioluminescence assay technique has been widely performed for cell cultures lacking the multicellular complexity and intercellular communications that exist in real tissues. 3D organoids present unique opportunities to investigate the functions of circadian rhythms in multicellular systems in vitro. For example, one could investigate circadian rhythms in the organoids with altered cell compositions or organoids derived from patients&#39; diseased tissues. This protocol enables the utilization of a bioluminescence assay to investigate different aspects of circadian rhythms in a more physiologically relevant in vitro model, organoids, which will help us better understand the roles of circadian rhythms in peripheral organs.

<table><tbody><tr><td>35 x 10 Falcon tissue culture dishes</td><td>Fisher Scientific</td><td>08-772A</td><td></td></tr><tr><td>A 83-01</td><td>Sigma Aldrich</td><td>SML0788</td><td></td></tr><tr><td>Advanced DMEM/F12</td><td>Life Technologies</td><td>12634-028</td><td></td></tr><tr><td>B-27 Supplement (50x)</td><td>Gibco</td><td>17504-044</td><td></td></tr><tr><td>BD Micro-Fine IV Insulin Syringes</td><td>Fisher Scientific</td><td>14-829-1Bb</td><td>Mfrn: BD 329424</td></tr><tr><td>CHIR99021</td><td>Cayman Chemical</td><td>13122</td><td>GSK-3 inhibitor</td></tr><tr><td>Dexamethasone</td><td>Sigma Aldrich</td><td>D4902-500MG</td><td></td></tr><tr><td>D-Luciferin (potassium salt)</td><td>Cayman Chemical</td><td>14681</td><td></td></tr><tr><td>Gastrin I Human</td><td>Sigma Aldrich</td><td>G9020</td><td></td></tr><tr><td>GlutaMAX</td><td>Gibco</td><td>35050061</td><td></td></tr><tr><td>Growth Factor reduced (GFR) Matrigel</td><td>Corning</td><td>CB-40230C</td><td></td></tr><tr><td>HEPES</td><td>Gibco</td><td>15630080</td><td></td></tr><tr><td>IntestiCult Organoid Growth Medium (Human)</td><td>Stemcell Technologies</td><td>06010</td><td>Consist of IntestiCult OGM Human Basal Medium, 50 mL and Organoid Supplement, 50 mL. Mix both as 1:1 ratio to use as intestinal organoid growth medium</td></tr><tr><td>Kronos Dio Luminometer Machine</td><td>ATTO Corporation</td><td>AB-2550</td><td></td></tr><tr><td>N-2 Supplement (100x)</td><td>Gibco</td><td>17502-048</td><td></td></tr><tr><td>N-Acetyl-L-cysteine</td><td>Sigma Aldrich</td><td>A9165</td><td></td></tr><tr><td>pABpuro-BluF reporter plasmid</td><td>Addgene</td><td>46824</td><td></td></tr><tr><td>PBS without Calcium and Magnesium</td><td>Corning</td><td>21-040-CV</td><td></td></tr><tr><td>Penicillin-Streptomycin</td><td>Gibco</td><td>15140122</td><td></td></tr><tr><td>Recombinant murine EGF</td><td>PeproTech</td><td>315-09</td><td></td></tr><tr><td>Y-27632</td><td>R&amp;amp;D Systems</td><td>1254/10</td><td>ROCK inhibitor</td></tr></tbody></table>

monitoring circadian oscillations with a bioluminescence reporter in organoids

Most living organisms possess circadian rhythms, which are biological processes that occur within a period of approximately 24 h and regulate a diverse repertoire of cellular and physiological processes ranging from sleep-wake cycles to metabolism. This clock mechanism entrains the organism based on environmental changes and coordinates the temporal regulation of molecular and physiological events. Previously, it was demonstrated that autonomous circadian rhythms are maintained even at the single-cell level using cell lines such as NIH3T3 fibroblasts, which were instrumental in uncovering the mechanisms of circadian rhythms. However, these cell lines are homogeneous cultures lacking multicellularity and robust intercellular communications. In the past decade, extensive work has been performed on the development, characterization, and application of 3D organoids, which are in vitro multicellular systems that resemble in vivo morphological structures and functions. This paper describes a protocol for detecting circadian rhythms using a bioluminescent reporter in human intestinal enteroids, which enables the investigation of circadian rhythms in multicellular systems in vitro.

Bioluminescence recording was conducted to assess the circadian rhythmicity of human intestinal enteroids (HIEs) under two distinct conditions: stem cell-enriched conditions using intestinal organoid growth medium (Figure 3) versus differentiation-inducing conditions, which was achieved by replacing the intestinal organoid growth medium with a differentiation medium. On the day of the experiment, we synchronized the circadian clocks by performing a 1 h treatment with 100 nM Dexamethasone. Su...

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Author Spotlight: In Vitro Investigations of Circadian Rhythms in Multicellular Systems

Circadian rhythms, which exist in most organisms, regulate the temporal organization of biological processes. 3D organoids have recently emerged as a physiologically relevant in vitro model. This protocol describes the use of bioluminescent reporters to observe circadian rhythms in organoids, enabling in vitro investigations of circadian rhythms in multicellular systems.

Monitoring Circadian Oscillations with a Bioluminescence Reporter in Organoids

Most living organisms possess circadian rhythms, which are biological processes that occur within a period of approximately 24 h and regulate a diverse ...

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Research

JoVE Journal

Biology

978 Views.  University of Cincinnati College of Medicine. Ons huidige onderzoeksgebied is het onderzoeken van de rol van circadiane ritmes bij de proliferatie en differentiatie van darmepitheelcellen. We proberen te bepalen of de circadiane klok de celproliferatie en differentiatie van intestinale stamcellen reguleert. Dit protocol presenteert een real-time monitoringmethode voor circadiane studies in driedimensionale organoïden met behulp van een bioluminescentietest.In tegenstelling tot het uitvoeren van bioluminescentietesten in een conve...

Video: Auteur in de schijnwerpers: In vitro onderzoek naar circadiane ritmes in meercellige systemen

Monitoring Actin Disassembly with Time-lapse Microscopy

Okay, so what I'd like to do today is to show you how to construct a flow chamber, a fusion chamber for imaging on an upright microscope. What then I then do is I create two spaces using film. So what I do is I take the para film, I cut it into small strips.Next I'm going to, this will basically form the channels for the, the walls, and I dry them with a tilted air. I put the cover slip on top of the para, And here's the finished. Then I heat it on a heat block to melt the param and basically create a seal.So what this is, is the, the cover glass here, and then on top of the cover glass is two layers of phim as you see right here. And then on top of this, again, there's a, it's a 22 by two two mil meter cover slip. This one right here, which I pressed against the param to fall the seal.Okay, so the liquid goes in in one direction here and I can suck it out with a filter paper here in this direction. And I'll show you how to do that in a bit. So what I like to do is I like to put it in a humidified chamber, which is very simple.Take two kind of elevated strips and have a filter of paper underneath. And to keep it noisy as I, I put the cover, cover slip on the flow chamber on. Now the way you introduce a solution to the chamber is that you just put the pipet tip at the entrance of the chamber and you just split.Now what I do is I incubate the chamber with the lid closed for 10 minutes. What I usually do to suck the liquid out from the other side is to use it, get a filter paper and cut it into thin strips like this. And I take one of these thin strips and I simultaneously apply the solution into the entrance while putting the filter paper at the exit to suck the exchange, the solution.So you'll see the liquid flowing through the solution. And then I wait for five minutes for the mid close. Now what I'm ready to do is to actually put that the actin it and the actin, I actually have to polymerize, I polymerize inside the flow chamber and it's just the same procedures before.So because like this, and then now that the action is polymerized, I wash out all the un excess un polymerized action using a large volume of just buffer. So here I have about a hundred microliters and it's a few reaction chamber volumes worth of buffer. Just, you know, when the filter paper becomes saturated, I have to change the direction.Okay?And so I'm ready to do imaging with this. So perfusion chamber with actin attached to it. Now I take the slide, mount it under the microscope, and since I'm imaging with an oil objective, I'm gonna put some immersion oil on the top surface of the cover, grass touch, such so assess solution or protein or anything on acting inside.So what I do is I can actually exchange the solution side while I'm doing the time lapse imaging. As such.

Parallel Measurement of Circadian Clock Gene Expression and Hormone Secretion in Human Primary Cell Cultures

Circadian clocks are functional in all light-sensitive organisms, allowing for an adaptation to the external world by anticipating daily environmental changes. Considerable progress in our understanding of the tight connection between the circadian clock and most aspects of physiology has been made in the field over the last decade. However, unraveling the molecular basis that underlies the function of the circadian oscillator in humans stays of highest technical challenge. Here, we provide a detailed description of an experimental approach for long-term (2-5 days) bioluminescence recording and outflow medium collection in cultured human primary cells. For this purpose, we have transduced primary cells with a lentiviral luciferase reporter that is under control of a core clock gene promoter, which allows for the parallel assessment of hormone secretion and circadian bioluminescence. Furthermore, we describe the conditions for disrupting the circadian clock in primary human cells by transfecting siRNA targeting CLOCK. Our results on the circadian regulation of insulin secretion by human pancreatic islets, and myokine secretion by human skeletal muscle cells, are presented here to illustrate the application of this methodology. These settings can be used to study the molecular makeup of human peripheral clocks and to analyze their functional impact on primary cells under physiological or pathophysiological conditions.

Here, we describe settings to monitor in parallel circadian bioluminescence and the secretory activity of human islet cells and primary myotubes. For this, we employed lentiviral gene delivery of a luciferase core clock reporter, followed by in vitro synchronization and collection of outflow medium by continuous cell perifusion.

Circadian clocks are functional in all light-sensitive organisms, allowing for an adaptation to the external world by anticipating daily environmental ...

Genetics

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells

The circadian rhythm is a fundamental physiological process present in all organisms that regulates biological processes ranging from gene expression to sleep behavior. In vertebrates, circadian rhythm is controlled by a molecular oscillator that functions in both the suprachiasmatic nucleus (SCN; central pacemaker) and individual cells comprising most peripheral tissues. More importantly, disruption of circadian rhythm by exposure to light-at-night, environmental stressors and/or toxicants is associated with increased risk of chronic diseases and aging. The ability to identify agents that can disrupt central and/or peripheral biological clocks, and agents that can prevent or mitigate the effects of circadian disruption, has significant implications for prevention of chronic diseases. Although rodent models can be used to identify exposures and agents that induce or prevent/mitigate circadian disruption, these experiments require large numbers of animals. In vivo studies also require significant resources and infrastructure, and require researchers to work all night. Thus, there is an urgent need for a cell-type appropriate in vitro system to screen for environmental circadian disruptors and enhancers in cell types from different organs and disease states. We constructed a vector that drives transcription of the destabilized luciferase in eukaryotic cells under the control of the human PERIOD 2 gene promoter. This circadian reporter construct was stably transfected into human mammary epithelial cells, and circadian responsive reporter cells were selected to develop the in vitro bioluminescence assay. Here, we present a detailed protocol to establish and validate the assay. We further provide details for proof of concept experiments demonstrating the ability of our in vitro assay to recapitulate the in vivo effects of various chemicals on the cellular biological clock. The results indicate that the assay can be adapted to a variety of cell types to screen for both environmental disruptors and chemopreventive enhancers of circadian clocks.

In Vitro Bioluminescence Assay to Characterize Circadian Rhythm in Mammary Epithelial Cells

An in vitro bioluminescence assay to determine cellular circadian rhythm in mammary epithelial cells is presented. This method utilizes mammalian cell reporter plasmids expressing destabilized luciferase under the control of the PERIOD 2 gene promoter. It can be adapted to other cell types to evaluate organ-specific effects on circadian rhythm.

The circadian rhythm is a fundamental physiological process present in all organisms that regulates biological processes ranging from gene expression to ...

Slice Preparation, Organotypic Tissue Culturing and Luciferase Recording of Clock Gene Activity in the Suprachiasmatic Nucleus

A central circadian (~24 hr) clock coordinating daily rhythms in physiology and behavior resides in the suprachiasmatic nucleus (SCN) located in the anterior hypothalamus. The clock is directly synchronized by light via the retina and optic nerve. Circadian oscillations are generated by interacting negative feedback loops of a number of so called "clock genes" and their protein products, including the Period (Per) genes. The core clock is also dependent on membrane depolarization, calcium and cAMP 1. The SCN shows daily oscillations in clock gene expression, metabolic activity and spontaneous electrical activity. Remarkably, this endogenous cyclic activity persists in adult tissue slices of the SCN 2-4. In this way, the biological clock can easily be studied in vitro, allowing molecular, electrophysiological and metabolic investigations of the pacemaker function.
The SCN is a small, well-defined bilateral structure located right above the optic chiasm 5. In the rat it contains ~8.000 neurons in each nucleus and has dimensions of approximately 947 &mu;m (length, rostrocaudal axis) x 424 &mu;m (width) x 390 &mu;m (height) 6. To dissect out the SCN it is necessary to cut a brain slice at the specific level of the brain where the SCN can be identified. Here, we describe the dissecting and slicing procedure of the SCN, which is similar for mouse and rat brains. Further, we show how to culture the dissected tissue organotypically on a membrane 7, a technique developed for SCN tissue culture by Yamazaki et al. 8. Finally, we demonstrate how transgenic tissue can be used for measuring expression of clock genes/proteins using dynamic luciferase reporter technology, a method that originally was used for circadian measurements by Geusz et al. 9. We here use SCN tissues from the transgenic knock-in PERIOD2::LUCIFERASE mice produced by Yoo et al. 10. The mice contain a fusion protein of PERIOD (PER) 2 and the firefly enzyme LUCIFERASE. When PER2 is translated in the presence of the substrate for luciferase, i.e. luciferin, the PER2 expression can be monitored as bioluminescence when luciferase catalyzes the oxidation of luciferin. The number of emitted photons positively correlates to the amount of produced PER2 protein, and the bioluminescence rhythms match the PER2 protein rhythm in vivo 10. In this way the cyclic variation in PER2 expression can be continuously monitored real time during many days. The protocol we follow for tissue culturing and real-time bioluminescence recording has been thoroughly described by Yamazaki and Takahashi 11.

The procedure of preparing slices containing the adult mouse hypothalamic suprachiasmatic nucleus (SCN), and a rapid way to culture the SCN tissue in organotypic culture condition, are reported. Further, the measurement of oscillatory clock gene protein expression using dynamic luciferase reporter technology is described.

A central circadian (~24 hr) clock coordinating daily rhythms in physiology and behavior resides in the suprachiasmatic nucleus (SCN) located in the ...

Neuroscience

An Optogenetic Method to Control and Analyze Gene Expression Patterns in Cell-to-cell Interactions

Cells should respond properly to temporally changing environments, which are influenced by various factors from surrounding cells. The Notch signaling pathway is one of such essential molecular machinery for cell-to-cell communications, which plays key roles in normal development of embryos. This pathway involves a cell-to-cell transfer of oscillatory information with ultradian rhythms, but despite the progress in molecular biology techniques, it has been challenging to elucidate the impact of multicellular interactions on oscillatory gene dynamics. Here, we present a protocol that permits optogenetic control and live monitoring of gene expression patterns in a precise temporal manner. This method successfully revealed that intracellular and intercellular periodic inputs of Notch signaling entrain intrinsic oscillations by frequency tuning and phase shifting at the single-cell resolution. This approach is applicable to the analysis of the dynamic features of various signaling pathways, providing a unique platform to test a functional significance of dynamic gene expression programs in multicellular systems.

Here, we present a protocol to analyze cell-to-cell transfer of oscillatory information by optogenetic control and live monitoring of gene expression. This approach provides a unique platform to test a functional significance of dynamic gene expression programs in multicellular systems.

Cells should respond properly to temporally changing environments, which are influenced by various factors from surrounding cells. The Notch signaling ...

Real-time Bioluminescence Imaging of Notch Signaling Dynamics during Murine Neurogenesis

Notch signaling regulates the maintenance of neural stem/progenitor cells by cell-cell interactions. The components of Notch signaling exhibit dynamic expression. Notch signaling effector Hes1 and the Notch ligand Delta-like1 (Dll1) are expressed in an oscillatory manner in neural stem/progenitor cells. Because the period of the oscillatory expression of these genes is very short (2 h), it is difficult to monitor their cyclic expression. To examine such rapid changes in the gene expression or protein dynamics, fast response reporters are required. Because of its fast maturation kinetics and high sensitivity, the bioluminescence reporter luciferase is suitable to monitor rapid gene expression changes in living cells. We used a destabilized luciferase reporter for monitoring the promoter activity and a luciferase-fused reporter for visualization of protein dynamics at single cell resolution. These bioluminescence reporters show rapid turnover and generate very weak signals; therefore, we have developed a highly sensitive bioluminescence imaging system to detect such faint signals. These methods enable us to monitor various gene expression dynamics in living cells and tissues, which are important information to help understand the actual cellular states.

Neural stem/progenitor cells exhibit various expression dynamics of Notch signaling components that lead to different outcomes of cellular events. Such dynamic expression can be revealed by real-time monitoring, not by static analysis, using a highly sensitive bioluminescence imaging system that enables visualization of rapid changes in gene expressions.

Notch signaling regulates the maintenance of neural stem/progenitor cells by cell-cell interactions. The components of Notch signaling exhibit dynamic ...

Developmental Biology

In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters

This technique combines optical fiber mediated fluorescence recordings with the precise delivery of recombinant adeno-associated virus based gene reporters. This new and easy to use in vivo fluorescence monitoring system was developed to record the transcriptional rhythm of the clock gene, Cry1, in the suprachiasmatic nucleus (SCN) of freely moving mice. To do so, a Cry1 transcription fluorescence reporter was designed and packaged into Adeno-associated virus. Purified, concentrated virus was injected into the mouse SCN followed by the insertion of an optic fiber, which was then fixed onto the surface of the brain. The animals were returned to their home cages and allowed a 1-month post-operative recovery period to ensure sufficient reporter expression. Fluorescence was then recorded in freely moving mice via an in vivo monitoring system that was constructed at our institution. For the in vivo recording system, a 488 nm laser was coupled with a 1 &#215; 4 beam-splitter that divided the light into four laser excitation outputs of equal power. This setup enabled us to record from four animals simultaneously. Each of the emitted fluorescence signals was collected via a photomultiplier tube and a data acquisition card. In contrast to the previous bioluminescence in vivo circadian clock recording technique, this fluorescence in vivo recording system allowed the recording of circadian clock gene expression during the light cycle.

In Vivo Monitoring of Circadian Clock Gene Expression in the Mouse Suprachiasmatic Nucleus Using Fluorescence Reporters

This newly developed fluorescence-based technology enables long-term monitoring of the transcription of circadian clock genes in the suprachiasmatic nucleus (SCN) of freely moving mice in real-time and at a high temporal resolution.

This technique combines optical fiber mediated fluorescence recordings with the precise delivery of recombinant adeno-associated virus based gene ...

Single-cell Resolution Fluorescence Live Imaging of Drosophila Circadian Clocks in Larval Brain Culture

The circadian pacemaker circuit orchestrates rhythmic behavioral and physiological outputs coordinated with environmental cues, such as day/night cycles. The molecular clock within each pacemaker neuron generates circadian rhythms in gene expression, which underlie the rhythmic neuronal functions essential to the operation of the circuit. Investigation of the properties of the individual molecular oscillators in different subclasses of pacemaker neurons and their interaction with neuronal signaling yields a better understanding of the circadian pacemaker circuit. Here, we present a time-lapse fluorescent microscopy approach developed to monitor the molecular clockwork in clock neurons of cultured Drosophila larval brain. This method allows the multi-day recording of the rhythms of genetically encoded fluorescent circadian reporters at single-cell resolution. This setup can be combined with pharmacological manipulations to closely analyze real-time response of the molecular clock to various compounds. Beyond circadian rhythms, this multipurpose method in combination with powerful Drosophila genetic techniques offers the possibility to study diverse neuronal or molecular processes in live brain tissue.

Single-cell Resolution Fluorescence Live Imaging of Drosophila Circadian Clocks in Larval Brain Culture

The goal of this protocol is to establish ex vivo Drosophila larval brain culture optimized to monitor circadian molecular rhythms with long-term fluorescence time-lapse imaging. The application of this method to pharmacological assays is also discussed.

The circadian pacemaker circuit orchestrates rhythmic behavioral and physiological outputs coordinated with environmental cues, such as day/night cycles. ...

Monitoring Cell-autonomous Circadian Clock Rhythms of Gene Expression Using Luciferase Bioluminescence Reporters

In mammals, many aspects of behavior and physiology such as sleep-wake cycles and liver metabolism are regulated by endogenous circadian clocks (reviewed1,2). The circadian time-keeping system is a hierarchical multi-oscillator network, with the central clock located in the suprachiasmatic nucleus (SCN) synchronizing and coordinating extra-SCN and peripheral clocks elsewhere1,2. Individual cells are the functional units for generation and maintenance of circadian rhythms3,4, and these oscillators of different tissue types in the organism share a remarkably similar biochemical negative feedback mechanism. However, due to interactions at the neuronal network level in the SCN and through rhythmic, systemic cues at the organismal level, circadian rhythms at the organismal level are not necessarily cell-autonomous5-7. Compared to traditional studies of locomotor activity in vivo and SCN explants ex vivo, cell-based in vitro assays allow for discovery of cell-autonomous circadian defects5,8. Strategically, cell-based models are more experimentally tractable for phenotypic characterization and rapid discovery of basic clock mechanisms5,8-13.
Because circadian rhythms are dynamic, longitudinal measurements with high temporal resolution are needed to assess clock function. In recent years, real-time bioluminescence recording using firefly luciferase as a reporter has become a common technique for studying circadian rhythms in mammals14,15, as it allows for examination of the persistence and dynamics of molecular rhythms. To monitor cell-autonomous circadian rhythms of gene expression, luciferase reporters can be introduced into cells via transient transfection13,16,17 or stable transduction5,10,18,19. Here we describe a stable transduction protocol using lentivirus-mediated gene delivery. The lentiviral vector system is superior to traditional methods such as transient transfection and germline transmission because of its efficiency and versatility: it permits efficient delivery and stable integration into the host genome of both dividing and non-dividing cells20. Once a reporter cell line is established, the dynamics of clock function can be examined through bioluminescence recording. We first describe the generation of P(Per2)-dLuc reporter lines, and then present data from this and other circadian reporters. In these assays, 3T3 mouse fibroblasts and U2OS human osteosarcoma cells are used as cellular models. We also discuss various ways of using these clock models in circadian studies. Methods described here can be applied to a great variety of cell types to study the cellular and molecular basis of circadian clocks, and may prove useful in tackling problems in other biological systems.

Circadian clocks function within individual cells, i.e., they are cell-autonomous. Here, we describe methods for generating cell-autonomous clock models using non-invasive, luciferase-based real-time bioluminescence technology. Reporter cells provide tractable, functional model systems for studying circadian biology.

In mammals, many aspects of behavior and physiology such as sleep-wake cycles and liver metabolism are regulated by endogenous circadian clocks ...

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.

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

Genetically encoded luciferase is a popular non-invasive reporter of gene expression. Use of an automated longitudinal luciferase imaging gas- and temperature-optimized recorder (ALLIGATOR) enables longitudinal recording from bioluminescent cells under a wide range of conditions. Here we show how ALLIGATOR may be used in the context of circadian rhythms research.

Monitoring Circadian Oscillations with a Bioluminescence Reporter in Organoids

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