Low-light imaging technology in the life sciences

Assaying NanoLuc Luciferase Activity from mRNA-Injected Xenopus Embryos

The earliest steps of animal development depend upon posttranscriptional events that drive the embryonic cell cycle and guide cell fate decisions. The analysis of post-transcriptional regulatory events has relied upon the use of chimeric reporter mRNAs that encode firefly luciferase fused to potential regulatory sequences. A new and more sensitive luciferase developed recently called NanoLuc has the potential to improve reporter studies and provide new insights into the regulation of embryonic processes. Here I describe how to create and analyze reporter mRNAs encoding NanoLuc luciferase using extracts from microinjected Xenopus embryos.

Induction of luciferase activity under the control of an hsp70 promoter using high-intensity focused ultrasound: combination of bioluminescence and MRI imaging in three different tumour models

The in vivo temporal changes of luciferase activity were investigated under the control of an hsp70 promoter in three tumour models after the application of different intensities of high-intensity focused ultrasound (HIFU). Three cell lines, SCCVII, NIH3T3 and M21 were stably transfected with a plasmid containing the hsp70 promoter and luciferase reporter gene, and tumours were subcutaneously initiated into mice. At a size of 1300 ± 234 mm(3), the tumours were exposed to five intensities of continuous HIFU (802-1401-2157-3067-4133 W/cm(2)) for 20 sec. Bioluminescence and MR imaging were performed to assess luciferase activity and signal intensity changes in the tissue. The MRI scan protocol was pre- and post-contrast T1-wt-SE, T2-wt-FSE, DCE-MRI, diffusion-wt STEAM sequence, T2 relaxation time determination obtained on a 1.5-T GE MRI scanner. The NIH3T3 tumours showed the highest luciferase activity of 328.1 ± 7.1 fold at 24 h at a HIFU intensity of 3067 W/cm(2), the M21 tumours of 3.2 ± 0.6 fold 8 hours and the SCCVII tumours 2.9 ± 0.9 fold 4 hours post-HIFU at 2157 W/cm(2). The greatest increase in T2 signal intensity and T2 relaxation time of 20.7 ± 3.4% was seen in the SCCVII tumours. The highest contrast medium uptake of 10.1 ± 1.1% was noted in the M21 tumours, and 14.8 ± 1.9% in the SCCVII tumours. In all tumours, a significant increase in the diffusion coefficient was seen with increased HIFU intensity, the highest of which was 40.3 ± 4.1% in the SCCVII tumours. The three tumour cell lines stably transfected with the hsp70/luciferase gene showed differential luciferase activity, which peaked at different times after the application of HIFU and was dependant on tumour type and HIFU energy deposition.

The effect of high intensity focused ultrasound on luciferase activity on two tumor cell lines in vitro, under the control of a CMV promoter

In this study, we compared the effect of high intensity focused ultrasound (HIFU) and thermal stress on the luciferase activity, controlled by a cytomegaly virus (CMV) promoter in an in vitro model using two tumor cell lines (M21, SCCVII). HIFU was applied in a pulsed-wave mode with increasing voltage at constant pulse duration, or thermal stress was delivered over a range of temperatures (36-52 degrees C) for 5 min. The resulting luciferase activity was measured in live cells using a cooled CCD camera. Luciferase activity was measured at set time intervals over a total of 48 h post-stress. Compared to baseline, the luciferase activity of the M21 tumor cell line when exposed to HIFU was approximately 54.2+/-67.5% (p<0.01) higher at a temperature of 42 degrees C, and approximately 52.9+/-128.5% (p<0.01) higher at 44 degrees C. In the SCCVII tumor cell line, the luciferase activity after HIFU application was 55.4+/-66.6% (p<0.01) higher compared to baseline at a temperature of 42 degrees C. The M21 and SCCVII tumor cell line when exposed to thermal stress alone did not increase the luciferase activity. M21 and SCCVII tumor cells exposed to HIFU showed a maximum decrease in cell viability to 45.3+/-7.5% and 10.3+/-7.5%, respectively, and when exposed to thermal stress to 85.3+/-3.5% and 20.4+/-6.5%, respectively, compared to the untreated control. In M21 and SCCVII cells exposed to HIFU, free radicals could be detected using the dichlorofluorescein dye. Our findings demonstrate that HIFU can enhance the luciferase activity controlled by a CMV promoter. However it also has a higher damaging effect on the cells.

Tumor tissue characterization evaluating the luciferase activity under the control of a hsp70 promoter and MR imaging in three tumor cell lines

We investigated the luciferase activity under the control of a hsp70 promoter and MR imaging for three tumor cell lines. Three tumor cell lines, SCCVII, NIH3T3 and M21 were transfected with a plasmid containing the hsp70 promoter fragment and the luciferase reporter gene and grown in mice. Bioluminescence imaging of the tumors was performed every other day. MR imaging, pre- and post-contrast T1-wt SE, T2-wt FSE, Diffusion-wt STEAM-sequence, T2-time determination were obtained on a 1.5-T GE MRI scanner at a tumor size of 600-800 mm(3) and 1400-1600 mm(3). Comparing the different tumor sizes the luciferase activity of the M21 tumors increased about 149.3%, for the NIH3T3 tumors about 47.4% and for the SCCVII tumors about 155.8%. Luciferase activity of the M21 tumors (r=0.82, p<0.01) and the SCCVII tumors (r=0.62, p=0.03) correlated significant with the diffusion coefficient. In the NIH3T3 tumors the best correlation between the luciferase activity and the MRI parameter was seen for the SNR (T2) values (r=0.78, p<0.01). The luciferase activity per mm(3) tumor tissue correlated moderate with the contrast medium uptake (r=0.55, p=0.01) in the M21 tumors. In the NIH3T3 and SCCVII tumors a negative correlation (r=-0.78, p<0.01, respectively, r=-0.49, p=0.02) was found with the T2 time. Different tissue types have different luciferase activity under the control of the same hsp70 promoter. The combination of MR imaging with bioluminescence imaging improves the characterization of tumor tissue giving better information of this tissue on the molecular level.

In vitro effect of focused ultrasound or thermal stress on HSP70 expression and cell viability in three tumor cell lines

RATIONALE AND OBJECTIVES

In this study, we compared the effect of focused ultrasound with the effect of thermal stress on the induction of a heat inducible promoter in an in vitro model using three tumor cell lines (M21, SCCVII, and NIH3T3).

MATERIALS AND METHODS

We used a reporter construct that was generated using the stress-inducible promoter from the gene encoding a murine 70-kilodalton heat shock protein (Hsp70A.1) and a luciferase (luc) reporter plasmid. High-intensity focused ultrasound (HIFU) was applied in two different modes. In the first mode, an increasing voltage at constant pulse duration and in the second mode a constant voltage at increasing pulse duration was applied. HIFU or thermal stress was delivered over a range of temperatures (36-52 degrees C) for 5 minutes, and resulting luciferase activity was measured in live cells using a cooled charge-coupled device camera as a measure of reporter gene transcription. Luciferase activity was measured at set time intervals for a total of 108 hours post-stress.

RESULTS

Both methods induced the hsp70 promoter; however, the luciferase activity under the influence of HIFU, independent of the applied mode, and thermal stress differs despite the fact that the temperature was the same. In the M21 tumor cell line, the maximum luciferase activity after focused ultrasound application was 4818 +/- 1521% at a temperature of 48 degrees C and after thermal stress 4468.2 +/- 1890.2% at a temperature of 52 degrees C with a viability of 72.3 +/- 5.2% and 85 +/- 3.4%, respectively. In the SCC tumor cell line, the maximum luciferase activity after focused ultrasound application was 6743.0 +/- 3281.4% and after only thermal stress exposure was 3910.6 +/- 2189.0% at a temperature of 44 degrees C and 50 degrees C, respectively. At the highest luciferase activity, the portion of vital cells was 72.5 +/- 8.4% and 72.5 +/- 5.9% respectively. In the NIH3T3 tumor cell line the highest luciferase activity of 428510.6 +/- 26526.8% was seen at a temperature of 42 degrees C applying focused ultrasound. Under thermal stress it was 29221.3 +/- 7205.0% at a temperature of 50 degrees C. At the highest luciferase activity, the viability analysis showed 75.3 +/- 9.2% and 72.3 +/- 7.9% viable cells, respectively.

CONCLUSIONS

Focused ultrasound induces hsp70 expression like thermal stress alone; however, HIFU is capable of inducing expression at lower temperatures than heat stress alone, indicating that nonthermal effects also play a role on the induction of hsp70.

A genetic reporter of thermal stress defines physiologic zones over a defined temperature range

We define five unique cellular responses to thermal stress using a reporter construct generated using the stress-inducible promoter from the gene encoding a murine 70 kDa heat shock protein (Hsp70A.1) to express luciferase (luc). Thermal stress was delivered over a range of temperatures (42-68 degrees C) for 5 s to 20 min and luciferase activity was measured in live cells using a cooled CCD camera as a measure of reporter gene transcription. Reporter gene expression was assessed every 2 h for 10 h, and at 24 h post-stress. Expression patterns were validated for selected temperatures. A transition zone where cells lose the ability to produce light and beyond which >50% of cells die was observed to occur within a narrow (2.5 degrees C) temperature window. Although luc and hsp70 mRNA levels in this transition zone were high, there were reduced levels of Luc and Hsp70 protein and ATP levels. Cells treated at these temperatures recovered the ability to produce light in response to a secondary stress at 30 h. This Hsp70-luc reporter gene construct may be useful for defining zones of physiologic responses and assessing collateral thermal damage generated during treatment of biological tissue with lasers and other sources of heat.

Current Advances in Molecular Imaging: Noninvasive in Vivo Bioluminescent and Fluorescent Optical Imaging in Cancer Research

Recently, there has been tremendous interest in developing techniques such as MRI, micro-CT, micro-PET, and SPECT to image function and processes in small animals. These technologies offer deep tissue penetration and high spatial resolution, but compared with noninvasive small animal optical imaging, these techniques are very costly and time consuming to implement. Optical imaging is cost-effective, rapid, easy to use, and can be readily applied to studying disease processes and biology in vivo. In vivo optical imaging is the result of a coalescence of technologies from chemistry, physics, and biology. The development of highly sensitive light detection systems has allowed biologists to use imaging in studying physiological processes. Over the last few decades, biochemists have also worked to isolate and further develop optical reporters such as GFP, luciferase, and cyanine dyes. This article reviews the common types of fluorescent and bioluminescent optical imaging, the typical system platforms and configurations, and the applications in the investigation of cancer biology.

Imaging of immobilized enzyme spots by scanning chemiluminescence microscopy with electrophoretic injection

Scanning chemiluminescence microscopy (SCLM) with electrophoretic injection was developed and applied to visualize enzyme reactions localized in an enzyme microspot. The SCLM uses a tapered glass capillary as a probe for injecting a small amount of luminol onto the substrate to generate localized chemiluminescence. The electrophoretic injection by application of a constant current between the inside and outside of the capillary enabled the continuous and controllable injection of a minute quantity of luminol in the range of 0.1 pmol/s. The image of enzyme activity in a monolayer spot of horseradish peroxidase was obtained by using the electrophoretic injection-based SCLM system.

Advancing Molecular Therapies through In Vivo Bioluminescent Imaging

Effective development of therapeutics that target the molecular basis of disease is dependent on testing new therapeutic moieties and delivery strategies in animal models of human disease. Accelerating the analyses of these models and improving their predictive value through whole animal imaging methods, which provide data in real time and are sensitive to the subtle changes, are crucial for rapid advancement of these approaches. Modalities based on optics are rapid, sensitive, and accessible methods for in vivo analyses with relatively low instrumentation costs. In vivo bioluminescent imaging (BLI) is one of these optically based imaging methods that enable rapid in vivo analyses of a variety of cellular and molecular events with extreme sensitivity. BLI is based on the use of light-emitting enzymes as internal biological light sources that can be detected externally as biological indicators. BLI has been used to test spatio-temporal expression patterns of both target and therapeutic genes in living laboratory animals where the contextual influences of whole biological systems are preserved. BLI has also been used to analyze gene delivery, immune cell therapies, and the in vivo efficacy of inhibitory RNAs. New tools for BLI are being developed that will offer greater flexibility in detection and analyses. BLI can be used to accelerate the evaluation of experimental therapeutic strategies and whole body imaging offers the opportunity of revealing the effects of novel approaches on key steps in disease processes.

It's not just about anatomy: in vivo bioluminescence imaging as an eyepiece into biology

Among the newly described tools that enable analyses of cellular and molecular events in living animals, in vivo bioluminescence imaging (BLI) offers important opportunities for investigating a wide variety of disease processes. BLI utilizes luciferase as an internal biological light source that can be genetically programmed to noninvasively "report" the presence or activation of specific biological events. Applications of BLI have included the use of luciferase to demonstrate expression of cell- and tissue-specific promoters, label cell populations, guide detection by other imaging modalities, and detect protein-protein interaction. These applications of BLI technology have allowed quantitative measurements of tumor burden and treatment response, immune cell trafficking, and detection of gene transfer. Spatiotemporal information can be rapidly obtained in the context of whole biological systems in vivo, which can accelerate the development of experimental therapeutic strategies. This paper provides a review of the biological applications in which in vivo BLI has been utilized to nondestructively monitor biological processes in intact small animal models, and highlights some of the advancements that will increase the versatility of BLI as a molecular imaging tool.

Imaging of light emission from the expression of luciferases in living cells and organisms: a review

Luciferases are enzymes that emit light in the presence of oxygen and a substrate (luciferin) and which have been used for real-time, low-light imaging of gene expression in cell cultures, individual cells, whole organisms, and transgenic organisms. Such luciferin-luciferase systems include, among others, the bacterial lux genes of terrestrial Photorhabdus luminescens and marine Vibrio harveyi bacteria, as well as eukaryotic luciferase luc and ruc genes from firefly species (Photinus) and the sea pansy (Renilla reniformis), respectively. In various vectors and in fusion constructs with other gene products such as green fluorescence protein (GFP; from the jellyfish Aequorea), luciferases have served as reporters in a number of promoter search and targeted gene expression experiments over the last two decades. Luciferase imaging has also been used to trace bacterial and viral infection in vivo and to visualize the proliferation of tumour cells in animal models.

Confocal microscopy and microbial viability detection for food research

Confocal microscopy offers several advantages over other conventional microscopic techniques as a tool for studying the interaction of bacteria with food and the role of food microstructure in product quality and safety. When using confocal microscopy, samples can be observed without extensive preparation processes, which allows for the evaluation of food without introducing artifacts. In addition, observations can be made in three dimensions without physically sectioning the specimen. The confocal microscope can be used to follow changes over a period of time, such as the development of the food structure or changes in microbial population during a process. Microbial attachment to and detachment from food and food contact surfaces with complex three-dimensional (3-D) structures can be observed in situ. The fate of microbial populations in food system depends on processing, distribution, and storage conditions as well as decontamination procedures that are applied to inactivate and remove them. The ability to determine the physiological status of microorganisms without disrupting their physical relationship with a food system can be useful for determining the means by which microorganisms survive decontamination treatments. Conventional culturing techniques can detect viable cells; however, these techniques lack the ability to locate viable cells in respect to the microscopic structures of food. Various microscopic methods take advantage of physiological changes in bacterial cells that are associated with the viability to assess the physiologic status of individual cells while retaining the ability to locate the cell within a food tissue system. This paper reviews the application of confocal microscopy in food research and direct observation of viable bacteria with emphasis on their use in food microbiology.

Development of an ultralow-light-level luminescence image analysis system for dynamic measurements of transcriptional activity in living and migrating cells

We have developed an approach to study in single living epithelial cells both cell migration and transcriptional activation, which was evidenced by the detection of luminescence emission from cells transfected with luciferase reporter vectors. The image acquisition chain consists of an epifluorescence inverted microscope, connected to an ultralow-light-level photon-counting camera and an image-acquisition card associated to specialized image analysis software running on a PC computer. Using a simple method based on a thin calibrated light source, the image acquisition chain has been optimized following comparisons of the performance of microscopy objectives and photon-counting cameras designed to observe luminescence. This setup allows us to measure by image analysis the luminescent light emitted by individual cells stably expressing a luciferase reporter vector. The sensitivity of the camera was adjusted to a high value, which required the use of a segmentation algorithm to eliminate the background noise. Following mathematical morphology treatments, kinetic changes of luminescent sources were analyzed and then correlated with the distance and speed of migration. Our results highlight the usefulness of our image acquisition chain and mathematical morphology software to quantify the kinetics of luminescence changes in migrating cells.

Biomass quantification by image analysis

Microbiologists have always rely on microscopy to examine microorganisms. When microscopy, either optical or electron-based, is coupled to quantitative image analysis, the spectrum of potential applications is widened: counting, sizing, shape characterization, physiology assessment, analysis of visual texture, motility studies are now easily available for obtaining information on biomass. In this chapter the main tools used for cell visualization as well as the basic steps of image treatment are presented. General shape descriptors can be used to characterize the cell morphology, but special descriptors have been defined for filamentous microorganisms. Physiology assessment is often based on the use of fluorescent dyes. The quantitative analysis of visual texture is still limited in bioengineering but the characterization of the surface of microbial colonies may open new prospects, especially for cultures on solid substrates. In many occasions, the number of parameters extracted from images is so large that data-mining tools, such as Principal Components Analysis, are useful for summarizing the key pieces of information.

Calcium imaging with chemiluminescence

This review updates the imaging of free cytosolic calcium with the chemiluminescent aequorins. Basic principles of chemiluminescence are discussed and the biochemistry of aequorins is briefly described. The review provides practical tips on handling and microinjecting aequorins and describes available ultra low light imaging systems. It is argued that aequorin-based calcium imaging is the method of choice for exploratory studies, since it is extremely sensitive, can detect a broad range of calcium concentrations, and allows for continuous recording during long periods of time. However, fluorescent methods are needed to attain high spatial resolution.

Applications of image analysis in cell technology

Image analysis is now a well established complement to optical microscopy, allowing routine quantification of microscopic observations. Recent method developments include location and enumeration of bacteria in solid foods, in situ microscopy and image analysis for on-line monitoring of yeast fermentations, and texture analysis of fungal colonies for subsequent transfer. Notable recent applications include studies on the pulsatile growth of hyphal apices, biochemical differentiation of fungal colonies, and simple structural differentiation of mycelia from submerged fungal cultures.