Name: autonomously bioluminescent mammalian cells for continuous and real-time monitoring of cytotoxicity
Uploaded: 2013-10-28T20:00:00
Description: Watch this Scientific Journal Video about Autonomously Bioluminescent Mammalian Cells for Continuous and Real-time Monitoring of Cytotoxicity at JoVE.com

These research efforts were supported by the National Science Foundation Division of Chemical, Bioengineering, Environmental, and Transport (CBET) Systems under award numbers CBET-0853780 and CBET-1159344 and the National Institutes of Health, National Institute of Environmental Health Sciences (NIEHS) under award number 1R43ES022567-01, and the National Cancer Institute, Cancer Imaging Program under award number CA127745-01. The IVIS Lumina instrument used in this work was obtained from the U.S. Army Defense University Research Instrumentation Program.

1. Cell Preparation
<ol>
	<li>Recover a vial of bioluminescent HEK293 cells from liquid nitrogen frozen stock and grow them in Dulbecco&#39;s Modified Eagle&#39;s medium (DMEM) supplemented with 10% fetal bovine serum, 0.01 mM nonessential amino acids, 1x&#160;antibiotic-antimycotic, and 0.01 mM sodium pyruvate in a T75 tissue culture flask at 37 &#176;C and 5% CO2. 
	Note: The media and supplemental components will vary based on cell lines and therefore should be chosen accordingly.</li>
	<l...

<ol>
	<li>U.S. Food and Drug Administration. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Is+it+really+FDA+approved?.">Is it really FDA approved?.</a> FDA Consumer Health Information. 2, (2009).</li><li>Hartung, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toxicology+for+the+twenty-first+century.">Toxicology for the twenty-first century.</a> Nature. 460, 208-212 (2009).</li><li>Olson, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Concordance+of+the+toxicity+of+pharmaceuticals+in+humans+and+in+animals.">Concordance of the toxicity of pharmaceuticals in humans and in animals.</a> Regul. Toxicol. Pharmacol. 32, 56-67 (2000).</li><li>Stacey, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+developments+in+cell+culture+technology.">Current developments in cell culture technology.</a> Adv. Exp. Med. Biol. 745, 1-13 (2012).</li><li>Li, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Screening+for+human+ADME/Tox+drug+properties+in+drug+discovery.">Screening for human ADME/Tox drug properties in drug discovery.</a> Drug Discov. Today. 6, 357-366 (2001).</li><li>Li, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+approaches+to+evaluate+ADMET+drug+properties.">In vitro approaches to evaluate ADMET drug properties.</a> Curr. Top. Med. Chem. 4, 701-706 (2004).</li><li>Tannous, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gaussia+luciferase+reporter+assay+for+monitoring+biological+processes+in+culture+and+in+vivo.">Gaussia luciferase reporter assay for monitoring biological processes in culture and in vivo.</a> Nat. Protoc. 4, 582-591 (2009).</li><li>Thompson, E. M., Nagata, S., Tsuji, F. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cloning+and+expression+of+cDNA+for+the+luciferase+from+the+marine+ostracod+Vargula+hilgendorfii.">Cloning and expression of cDNA for the luciferase from the marine ostracod Vargula hilgendorfii.</a> Proc. Natl. Acad. Sci. U.S.A. 86, 6567-6571 (1989).</li><li>Lupold, S. E., Johnson, T., Chowdhury, W. H., Rodriguez, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+real+time+Metridia+luciferase+based+non-invasive+reporter+assay+of+mammalian+cell+viability+and+cytotoxicity+via+the+beta-actin+promoter+and+enhancer.">A real time Metridia luciferase based non-invasive reporter assay of mammalian cell viability and cytotoxicity via the beta-actin promoter and enhancer.</a> PLoS ONE. 7, (2012).</li><li>Meighen, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+biology+of+bacterial+bioluminescence.">Molecular biology of bacterial bioluminescence.</a> Microbiol. Rev. 55, 123-142 (1991).</li><li>Close, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autonomous+bioluminescent+expression+of+the+bacterial+luciferase+gene+cassette+(lux)+in+a+mammalian+cell+line.">Autonomous bioluminescent expression of the bacterial luciferase gene cassette (lux) in a mammalian cell line.</a> PLoS ONE. 5, e12441 (2010).</li><li>Close, D. M., Hahn, R. E., Ripp, S. A., Sayler, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determining+toxicant+bioavailability+using+a+constitutively+bioluminescent+human+cell+line.">Determining toxicant bioavailability using a constitutively bioluminescent human cell line.</a> , 1-4 (2011).</li><li>Oliva-Trastoy, M., Defais, M., Larminat, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resistance+to+the+antibiotic+Zeocin+by+stable+expression+of+the+Sh+ble+gene+does+not+fully+suppress+Zeocin-induced+DNA+cleavage+in+human+cells.">Resistance to the antibiotic Zeocin by stable expression of the Sh ble gene does not fully suppress Zeocin-induced DNA cleavage in human cells.</a> Mutagenesis. 20, 111-114 (2005).</li><li>Close, D. M., Webb, J. D., Ripp, S. A., Patterson, S. S., Sayler, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remote+detection+of+human+toxicants+in+real+time+using+a+human+optimized+bioluminescent+bacterial+luciferase+gene+cassette+bioreporter.">Remote detection of human toxicants in real time using a human optimized bioluminescent bacterial luciferase gene cassette bioreporter.</a> Proc. SPIE 8371, Sensing Technologies for Global Health, Military Medicine, Disaster Response, and Environmental Monitoring II; and Biometric Technology for Human Identification IX. 837117, (2012).</li><li>Close, D. M., Hahn, R. E., Patterson, S. S., Ripp, S. A., Sayler, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+human+optimized+bacterial+luciferase,+firefly+luciferase,+and+green+fluorescent+protein+for+continuous+imaging+of+cell+culture+and+animal+models.">Comparison of human optimized bacterial luciferase, firefly luciferase, and green fluorescent protein for continuous imaging of cell culture and animal models.</a> J. Biomed. Opt. 16, e12441 (2011).</li></ol>

This method demonstrates the use of autonomously bioluminescent mammalian cells as an in vitro cytotoxicity screening assay that allows live cells to be continuously monitored over their lifetime. This protocol is flexible and can be modified to accommodate specific experimental conditions as required. For example, the experiment presented here is suitable for tracking acute toxic effects, but can be adapted to assess slow-acting or long term effects by repeatedly imaging at increased time intervals (i.e.</e...

In the U.S., pharmaceuticals and other products intended for human consumption require extensive assessment before they are approved for consumer use by the Food and Drug Administration. The financial burden for performing this testing is placed on the developer1, which substantially increases the cost of new compound development and therefore translates into an increased cost for consumers. While traditionally much of this screening has utilized animal subjects to act as proxies for human hosts, this has proven to be a large financial burden, with an estimated $2.8 billion spent annually on ADME/Tox (adsorption, distribution, metabolism, excretion, and toxicity) screening alone2&#160;and mounting evidence suggesting that animal models cannot reliably predict human toxicological responses3. Therefore, in vitro human cell culture-based testing has gained popularity over the past two decades because of its relatively lower cost, higher throughput, and better representation of human bioavailability and toxicology4. Current cell culture-based toxicity screening methods employ various endpoints, such as the measurement of ATP levels, screening the activity of endogenously available cytoplasmic enzymes, probing the integrity of the cellular membrane, or tracking the level of mitochondrial activity, to evaluate cellular viability5,6. However, regardless of the endpoint chosen, these methods all require the destruction of the sample before measurements can be taken, thus only producing data at a single time point. As a result, large numbers of samples need to be prepared and treated in parallel for basic toxicological kinetics studies, again adding to the cost and labor required for new compound development. Alternatively, assays using secreted luciferase such as Gaussia luciferase7, Vargula luciferase8, and Metridia luciferase9 have been developed that eliminate the need for cell lysis and require a fraction of the media for endpoint measurement, however, these are still limited to sampling at predetermined time points and also require the addition of exogenous light-activating substrates.
To avoid the detriment of requisite sample destruction as well as to eliminate the cost of substrates, a human cell line has been engineered that expresses the full bacterial bioluminescence (lux) gene cassette (luxCDABEfrp) to allow for continuous monitoring of live cells that is similar to fluorescent-dye based live cell imaging, but without the additional photon-activating and microscopic investigation procedures. This cell line is capable of constitutively producing an optical signal for continuous, direct detection without the need for external stimulation, thus avoiding destruction of the sample. Mechanistically, the bioluminescent signal generated from these cells results when the luxAB-formed luciferase enzyme catalyzes the oxidation of a long chain fatty aldehyde (synthesized and regenerated by the luxCDE gene products using endogenous substrates) in the presence of reduced riboflavin phosphate (FMNH2, which is recycled from FMN by the frp gene product) and molecular oxygen10. Expression of the lux cassette in the host cell therefore enables light to be produced and detected without cellular destruction or exogenous substrate addition. Similarly, the interaction between the lux genes and the endogenously available FMN, and O2 cosubstrates, and the requirement for maintenance of an environment that can support the conversion of FMN to FMNH2, ensures that the resulting bioluminescent signal can only be detected from living, metabolically active cells.
These requirements have previously been exploited to demonstrate that lux-based bioluminescent output correlates strongly with cellular population size11 and that toxic compound exposure impairs autobioluminescent production in a dose-response fashion12. Here we use a previously characterized autobioluminescent human embryonic kidney (HEK293) cell line11 to demonstrate the automated toxicological screening of an antibiotic of the bleomycin family with known DNA damaging activity as a representative example to validate the application of autobioluminescent mammalian cells for toxicity testing.

<table border="1">
	<tbody>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comment</td>
		</tr>
		<tr>
			<td>IVIS Lumina</td>
			<td>PerkinElmer</td>
			<td></td>
			<td>Other IVIS models and PMT-based plate readers can also be used</td>
		</tr>
		<tr>
			<td>Living Imaging 2.0</td>
			<td>PerkinElmer</td>
			<td></td>
			<td>Newer updates of this software is available</td>
		</tr>
		<tr>
			<td>75 cm2 cell culture treated flasks</td>
			<td>Corning</td>
			<td>430641</td>
			<td></td>
		</tr>
		<tr>
			<td>6-well tissue culture-treated plates</td>
			<td>Costar</td>
			<td>07-200-83</td>
			<td></td>
		</tr>
		<tr>
			<td>Black 24-well plate</td>
			<td>Greiner Bio-One</td>
			<td>662174</td>
			<td>96- or 384-well plates can be used for higher throughput applications</td>
		</tr>
		<tr>
			<td>Phosphate buffered saline</td>
			<td>Hyclone</td>
			<td>SH30910</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle&#39;s Medium (DMEM), phenol red-free</td>
			<td>Hyclone</td>
			<td>SH30284</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Hyclone</td>
			<td>SH3091003</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonessential amino acids, 100x</td>
			<td>Life Technologies</td>
			<td>11140050</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic-antimycotic, 100x</td>
			<td>Life Technologies</td>
			<td>15240062</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate, 100mM</td>
			<td>Life Technologies</td>
			<td>11360070</td>
			<td></td>
		</tr>
		<tr>
			<td>Zeocin, 100 mg/ml</td>
			<td>Life Technologies</td>
			<td>R25001</td>
			<td></td>
		</tr>
		<tr>
			<td>Tripsin, 0.05%</td>
			<td>Life Technologies</td>
			<td>25300062</td>
			<td></td>
		</tr>
	</tbody>
</table>

autonomously bioluminescent mammalian cells for continuous and real-time monitoring of cytotoxicity

Mammalian cell-based in vitro assays have been widely employed as alternatives to animal testing for toxicological studies but have been limited due to the high monetary and time costs of parallel sample preparation that are necessitated due to the destructive nature of firefly luciferase-based screening methods. This video describes the utilization of autonomously bioluminescent mammalian cells, which do not require the destructive addition of a luciferin substrate, as an inexpensive and facile method for monitoring the cytotoxic effects of a compound of interest. Mammalian cells stably expressing the full bacterial bioluminescence (luxCDABEfrp) gene cassette autonomously produce an optical signal that peaks at 490 nm without the addition of an expensive and possibly interfering luciferin substrate, excitation by an external energy source, or destruction of the sample that is traditionally performed during optical imaging procedures. This independence from external stimulation places the burden for maintaining the bioluminescent reaction solely on the cell, meaning that the resultant signal is only detected during active metabolism. This characteristic makes the lux-expressing cell line an excellent candidate for use as a biosentinel against cytotoxic effects because changes in bioluminescent production are indicative of adverse effects on cellular growth and metabolism. Similarly, the autonomous nature and lack of required sample destruction permits repeated imaging of the same sample in real-time throughout the period of toxicant exposure and can be performed across multiple samples using existing imaging equipment in an automated fashion.

In this study, the dynamics of autobioluminescent HEK293 cells were monitored continuously over a 24 hr period in response to antibiotic exposure (Figure 1). The toxic effects of this antibiotic, which is a member of the bleomycin family known to kill living cells by binding to and cleaving DNA13, were demonstrated via a decrease in bioluminescent production compared to untreated cells, which can be directly visualized through the pseudocolor images (Figure 2). The autobiolumi...

Watch this Scientific Journal Video about Autonomously Bioluminescent Mammalian Cells for Continuous and Real-time Monitoring of Cytotoxicity at JoVE.com

Autonomously Bioluminescent Mammalian Cells for Continuous and Real-time Monitoring of Cytotoxicity

Mammalian cells expressing the bacterial bioluminescence gene cassette (lux) produce light autonomously. The resulting bioluminescent dynamics upon chemical exposure have been demonstrated to reflect the treatment effects on cellular growth and metabolism, making these cells an inexpensive, continuous, real-time toxicity screening tool that can easily be adapted for high-throughput automation.

Mammalian  cell-based in vitro assays have been  widely employed as alternatives to animal testing for toxicological studies but  have been limited due to ...

autonomously-bioluminescent-mammalian-cells-for-continuous-real-time

Research

JoVE Journal

Biology

Trypsinizing and Subculturing Mammalian Cells

As cells reach confluency, they must be subcultured or passaged. Failure to subculture confluent cells results in reduced mitotic index and eventually in cell death. The first step in subculturing is to detach cells from the surface of the primary culture vessel by trypsinization or mechanical means. The resultant cell suspension is then subdivided, or reseeded, into fresh cultures. Secondary cultures are checked for growth and fed periodically, and may be subsequently subcultured to produce tertiary cultures. The time between passaging of cells varies with the cell line and depends on the growth rate.

As cells reach confluency, they must be subcultured or passaged. This video will demonstrate a procedure for subculturing both adherent and suspension cells.

As cells reach confluency, they must be subcultured or passaged. Failure to subculture confluent cells results in reduced mitotic index and eventually in ...

MISSION esiRNA for RNAi Screening in Mammalian Cells

RNA interference (RNAi) is a basic cellular mechanism for the control of gene expression. RNAi is induced by short double-stranded RNAs also known as small interfering RNAs (siRNAs). The short double-stranded RNAs originate from longer double stranded precursors by the activity of Dicer, a protein of the RNase III family of endonucleases. The resulting fragments are components of the RNA-induced silencing complex (RISC), directing it to the cognate target mRNA. RISC cleaves the target mRNA thereby reducing the expression of the encoded protein1,2,3. RNAi has become a powerful and widely used experimental method for loss of gene function studies in mammalian cells utilizing small interfering RNAs.
Currently two main methods are available for the production of small interfering RNAs. One method involves chemical synthesis, whereas an alternative method employs endonucleolytic cleavage of target specific long double-stranded RNAs by RNase III in vitro. Thereby, a diverse pool of siRNA-like oligonucleotides is produced which is also known as endoribonuclease-prepared siRNA or esiRNA. A comparison of efficacy of chemically derived siRNAs and esiRNAs shows that both triggers are potent in target-gene silencing. Differences can, however, be seen when comparing specificity. Many single chemically synthesized siRNAs produce prominent off-target effects, whereas the complex mixture inherent in esiRNAs leads to a more specific knockdown10.
In this study, we present the design of genome-scale MISSION esiRNA libraries and its utilization for RNAi screening exemplified by a DNA-content screen for the identification of genes involved in cell cycle progression. We show how to optimize the transfection protocol and the assay for screening in high throughput. We also demonstrate how large data-sets can be evaluated statistically and present methods to validate primary hits. Finally, we give potential starting points for further functional characterizations of validated hits.

Here we use a human esiRNA library in a high-throughput screen for genes involved in cell division. We demonstrate how to set up and conduct an esiRNA screens, as well as how to analyze and validate the results.

RNA interference (RNAi) is a basic cellular mechanism for the control of gene expression. RNAi is induced by short double-stranded RNAs also known as ...

Mutagenesis and Functional Analysis of Ion Channels Heterologously Expressed in Mammalian Cells

We will demonstrate how to study the functional effects of introducing a point mutation in an ion channel. We study G protein-gated inwardly rectifying potassium (referred to as GIRK) channels, which are important for regulating the excitability of neurons. There are four different mammalian GIRK channel subunits (GIRK1-GIRK4) - we focus on GIRK2 because it forms a homotetramer. Stimulation of different types of G protein-coupled receptors (GPCRs), such as the muscarinic receptor (M2R), leads to activation of GIRK channels. Alcohol also directly activates GIRK channels. We will show how to mutate one amino acid by specifically changing one or more nucleotides in the cDNA for the GIRK channel. This mutated cDNA sequence will be amplified in bacteria, purified, and the presence of the point mutation will be confirmed by DNA sequencing. The cDNAs for the mutated and wild-type GIRK channels will be transfected into human embryonic kidney HEK293T cells cultured in vitro. Lastly, whole-cell patch-clamp electrophysiology will be used to study the macroscopic potassium currents through the ectopically expressed wild-type or mutated GIRK channels. In this experiment, we will examine the effect of a L257W mutation in GIRK2 channels on M2R-dependent and alcohol-dependent activation.

We will demonstrate how to study the effect of a single point mutation on the function of an ion channel.

We will demonstrate how to study the functional effects of introducing a point mutation in an ion channel. We study G protein-gated inwardly rectifying ...

Profiling of Pre-micro RNAs and microRNAs using Quantitative Real-time PCR (qPCR) Arrays

Quantitative real-time PCR (QPCR) has emerged as an accurate and valuable tool in profiling gene expression levels.  One of its many advantages is a lower detection limit compared to other methods of gene expression profiling while using smaller amounts of input for each assay.  Automated qPCR setup has improved this field by allowing for greater reproducibility.  Its convenient and rapid setup allows for high-throughput experiments, enabling the profiling of many different genes simultaneously in each experiment.  This method along with internal plate controls also reduces experimental variables common to other techniques.  
We recently developed a qPCR assay for profiling of pre-microRNAs  (pre-miRNAs) using a set of 186 primer pairs.  MicroRNAs have emerged as a novel class of small, non-coding RNAs with the ability to regulate many mRNA targets at the post-transcriptional level.  These small RNAs are first transcribed by RNA polymerase II as a primary miRNA (pri-miRNA) transcript, which is then cleaved into the precursor miRNA (pre-miRNA).  Pre-miRNAs are exported to the cytoplasm where Dicer cleaves the hairpin loop to yield mature miRNAs.  Increases in miRNA levels can be observed at both the precursor and mature miRNA levels and profiling of both of these forms can be useful.  There are several commercially available assays for mature miRNAs; however, their high cost may deter researchers from this profiling technique.  Here, we discuss a cost-effective, reliable, SYBR-based qPCR method of profiling pre-miRNAs.  Changes in pre-miRNA levels often reflect mature miRNA changes and can be a useful indicator of mature miRNA expression.  However, simultaneous profiling of both pre-miRNAs and mature miRNAs may be optimal as they can contribute nonredundant information and provide insight into microRNA processing.  Furthermore, the technique described here can be expanded to encompass the profiling of other library sets for specific pathways or pathogens.

Profiling of Pre-micro RNAs and microRNAs using Quantitative Real-time PCR qPCR Arrays

We will demonstrate the setup and analysis of pre-microRNA 96-well arrays for QPCR using a robot as well as by hand with a Thermo Scientific Matrix multichannel pipette.

Quantitative real-time PCR (QPCR) has emerged as an accurate and valuable tool in profiling gene expression levels.  One of its many advantages is a lower ...

Real-time Monitoring of Ligand-receptor Interactions with Fluorescence Resonance Energy Transfer

FRET is a process whereby energy is non-radiatively transferred from an excited donor molecule to a ground-state acceptor molecule through long-range dipole-dipole interactions1. In the present sensing assay, we utilize an interesting property of PDA: blue-shift in the UV-Vis electronic absorption spectrum of PDA (Figure 1) after an analyte interacts with receptors attached to PDA2,3,4,7. This shift in the PDA absorption spectrum provides changes in the spectral overlap (J) between PDA (acceptor) and rhodamine (donor) that leads to changes in the FRET efficiency. Thus, the interactions between analyte (ligand) and receptors are detected through FRET between donor fluorophores and PDA. In particular, we show the sensing of a model protein molecule streptavidin. We also demonstrate the covalent-binding of bovine serum albumin (BSA) to the liposome surface with FRET mechanism. These interactions between the bilayer liposomes and protein molecules can be sensed in real-time. The proposed method is a general method for sensing small chemical and large biochemical molecules. Since fluorescence is intrinsically more sensitive than colorimetry, the detection limit of the assay can be in sub-nanomolar range or lower8. Further, PDA can act as a universal acceptor in FRET, which means that multiple sensors can be developed with PDA (acceptor) functionalized with donors and different receptors attached on the surface of PDA liposomes.

We demonstrate FRET between conjugated polymer polydiacetylene (PDA) and fluorophore attached to the surface of PDA liposomes for the sensing of biomolecules. PDA liposomes also contained receptor molecules on their surfaces for biomolecules to be used as probes. Ligand-receptor interactions lead to changes in the FRET efficiency between the fluorophore and PDA which is the basis of the sensing mechanism.

FRET is a process  whereby energy is non-radiatively transferred from an excited donor molecule to  a ground-state acceptor molecule through long-range ...

FRET Microscopy for Real-time Monitoring of Signaling Events in Live Cells Using Unimolecular Biosensors

F&ouml;rster resonance energy transfer (FRET) microscopy continues to gain increasing interest as a technique for real-time monitoring of biochemical and signaling events in live cells and tissues. Compared to classical biochemical methods, this novel technology is characterized by high temporal and spatial resolution. FRET experiments use various genetically-encoded biosensors which can be expressed and imaged over time in situ or in vivo1-2. Typical biosensors can either report protein-protein interactions by measuring FRET between a fluorophore-tagged pair of proteins or conformational changes in a single protein which harbors donor and acceptor fluorophores interconnected with a binding moiety for a molecule of interest3-4. Bimolecular biosensors for protein-protein interactions include, for example, constructs designed to monitor G-protein activation in cells5, while the unimolecular sensors measuring conformational changes are widely used to image second messengers such as calcium6, cAMP7-8, inositol phosphates9 and cGMP10-11. Here we describe how to build a customized epifluorescence FRET imaging system from single commercially available components and how to control the whole setup using the Micro-Manager freeware. This simple but powerful instrument is designed for routine or more sophisticated FRET measurements in live cells. Acquired images are processed using self-written plug-ins to visualize changes in FRET ratio in real-time during any experiments before being stored in a graphics format compatible with the build-in ImageJ freeware used for subsequent data analysis. This low-cost system is characterized by high flexibility and can be successfully used to monitor various biochemical events and signaling molecules by a plethora of available FRET biosensors in live cells and tissues. As an example, we demonstrate how to use this imaging system to perform real-time monitoring of cAMP in live 293A cells upon stimulation with a &beta;-adrenergic receptor agonist and blocker.

F&#246;rster resonance energy transfer (FRET) microscopy is a powerful technique for real-time monitoring of signaling events in live cells using various biosensors as reporters. Here we describe how to build a customized epifluorescence FRET imaging system from commercially available components and how to use it for FRET experiments.

F&ouml;rster resonance energy transfer (FRET) microscopy  continues to gain increasing interest as a technique for real-time monitoring  of biochemical ...

Monitoring Plasmid Replication in Live Mammalian Cells over Multiple Generations by Fluorescence Microscopy

Few naturally-occurring plasmids are maintained in mammalian cells. Among these are genomes of gamma-herpesviruses, including Epstein-Barr virus (EBV) and Kaposi's Sarcoma-associated herpesvirus (KSHV), which cause multiple human malignancies 1-3. These two genomes are replicated in a licensed manner, each using a single viral protein and cellular replication machinery, and are passed to daughter cells during cell division despite their lacking traditional centromeres 4-8.
Much work has been done to characterize the replications of these plasmid genomes using methods such as Southern blotting and fluorescence in situ hybridization (FISH). These methods are limited, though. Quantitative PCR and Southern blots provide information about the average number of plasmids per cell in a population of cells. FISH is a single-cell assay that reveals both the average number and the distribution of plasmids per cell in the population of cells but is static, allowing no information about the parent or progeny of the examined cell.
Here, we describe a method for visualizing plasmids in live cells. This method is based on the binding of a fluorescently tagged lactose repressor protein to multiple sites in the plasmid of interest 9. The DNA of interest is engineered to include approximately 250 tandem repeats of the lactose operator (LacO) sequence. LacO is specifically bound by the lactose repressor protein (LacI), which can be fused to a fluorescent protein. The fusion protein can either be expressed from the engineered plasmid or introduced by a retroviral vector. In this way, the DNA molecules are fluorescently tagged and therefore become visible via fluorescence microscopy. The fusion protein is blocked from binding the plasmid DNA by culturing cells in the presence of IPTG until the plasmids are ready to be viewed.
This system allows the plasmids to be monitored in living cells through several generations, revealing properties of their synthesis and partitioning to daughter cells. Ideal cells are adherent, easily transfected, and have large nuclei. This technique has been used to determine that 84% of EBV-derived plasmids are synthesized each generation and 88% of the newly synthesized plasmids partition faithfully to daughter cells in HeLa cells. Pairs of these EBV plasmids were seen to be tethered to or associated with sister chromatids after their synthesis in S-phase until they were seen to separate as the sister chromatids separated in Anaphase10. The method is currently being used to study replication of KSHV genomes in HeLa cells and SLK cells. HeLa cells are immortalized human epithelial cells, and SLK cells are immortalized human endothelial cells. Though SLK cells were originally derived from a KSHV lesion, neither the HeLa nor SLK cell line naturally harbors KSHV genomes11. In addition to studying viral replication, this visualization technique can be used to investigate the effects of the addition, removal, or mutation of various DNA sequence elements on synthesis, localization, and partitioning of other recombinant plasmid DNAs.

A method of observing individual DNA molecules in live cells is described. The technique is based on the binding of a fluorescently tagged lac repressor protein to binding sites engineered into the DNA of interest. This method can be adapted to follow many recombinant DNAs in live cells over time.

Few naturally-occurring plasmids are maintained in mammalian cells.  Among these are genomes of gamma-herpesviruses, including Epstein-Barr virus  (EBV) ...

Measurement of Heme Synthesis Levels in Mammalian Cells

Heme serves as the prosthetic group for a wide variety of proteins known as hemoproteins, such as hemoglobin, myoglobin and cytochromes. It is involved in various molecular and cellular processes such as gene transcription, translation, cell differentiation and cell proliferation. The biosynthesis levels of heme vary across different tissues and cell types and is altered in diseased conditions such as anemia, neuropathy and cancer. This technique uses [4-14C] 5-aminolevulinic acid ([14C] 5-ALA), one of the early precursors in the heme biosynthesis pathway to measure the levels of heme synthesis in mammalian cells. This assay involves incubation of cells with [14C] 5-ALA followed by extraction of heme and measurement of the radioactivity incorporated into heme. This procedure is accurate and quick. This method measures the relative levels of heme biosynthesis rather than the total heme content. To demonstrate the use of this technique the levels of heme biosynthesis were measured in several mammalian cell lines.

Altered intracellular heme levels are associated with common diseases such as cancer. Thus, there is a need to measure heme biosynthesis levels in diverse cells. The goal of this protocol is to provide a fast and sensitive method to measure and compare the levels of heme synthesis in different cells.

Heme serves as the prosthetic group for a wide variety of proteins known as hemoproteins, such as hemoglobin, myoglobin and cytochromes. It is involved in ...

Probe-based Real-time PCR Approaches for Quantitative Measurement of microRNAs

Probe-based quantitative PCR (qPCR) is a favoured method for measuring transcript abundance, since it is one of the most sensitive detection methods that provides an accurate and reproducible analysis. Probe-based chemistry offers the least background fluorescence as compared to other (dye-based) chemistries. Presently, there are several platforms available that use probe-based chemistry to quantitate transcript abundance. qPCR in a 96 well plate is the most routinely used method, however only a maximum of 96 samples or miRNAs can be tested in a single run. This is time-consuming and tedious if a large number of samples/miRNAs are to be analyzed. High-throughput probe-based platforms such as microfluidics (e.g. TaqMan Array Card) and nanofluidics arrays (e.g. OpenArray) offer ease to reproducibly and efficiently detect the abundance of multiple microRNAs in a large number of samples in a short time. Here, we demonstrate the experimental setup and protocol for miRNA quantitation from serum or plasma-EDTA samples, using probe-based chemistry and three different platforms (96 well plate, microfluidics and nanofluidics arrays) offering increasing levels of throughput.

Circulating microRNAs have recently emerged as promising and novel biomarkers for various cancers and other diseases. The goal of this article is to discuss three different probe-based real-time PCR platforms and methods that are available to quantify and determine the abundance of circulating microRNAs.

Probe-based quantitative PCR (qPCR) is a favoured method for measuring transcript abundance, since it is one of the most sensitive detection methods that ...

In Situ Monitoring of Transiently Formed Molecular Chaperone Assemblies in Bacteria, Yeast, and Human Cells

J-domain proteins (JDPs) form the largest and the most diverse co-chaperone family in eukaryotic cells. Recent findings show that specific members of the JDP family could form transient heterocomplexes in eukaryotes to fine-tune substrate selection for the 70 kDa heat shock protein (Hsp70) chaperone-based protein disaggregases. The JDP complexes target acute/chronic stress induced aggregated proteins and presumably help assemble the disaggregases by recruiting multiple Hsp70s to the surface of protein aggregates. The extent of the protein quality control (PQC) network formed by these physically interacting JDPs remains largely uncharacterized in vivo. Here, we describe a microscopy-based in situ protein interaction assay named the proximity ligation assay (PLA), which is able to robustly capture&#160;these transiently formed chaperone complexes in distinct cellular compartments of eukaryotic cells. Our work expands the employment of PLA from human cells to yeast (Saccharomyces cerevisiae) and bacteria (Escherichia coli), thus rendering an important tool to monitor the dynamics of transiently formed protein assemblies in both prokaryotic and eukaryotic cells.

Cognate J-domain proteins cooperate with the Hsp70 chaperone to assist in a myriad of biological processes ranging from protein folding to degradation. Here, we describe an in situ proximity ligation assay, which allows the monitoring of these transiently formed chaperone machineries in bacterial, yeast and human cells.

J-domain proteins (JDPs) form the largest and the most diverse co-chaperone family in eukaryotic cells. Recent findings show that specific members of the ...