Low-light image analysis of transgenic organisms using bacterial luciferase as a marker

Real-Time Monitoring of Single Bacterium Lysis and Leakage Events by Chemiluminescence Microscopy

The small size of bacteria makes it difficult to study the biochemistry inside single cells. The amount of material inside is limited; therefore, an ultrasensitive method is required to interrogate single cells. Using a sensitive ICCD detector to record chemiluminescence (CL) from an optimized firefly luciferase-ATP bioluminescence reaction system, we report for the first time real-time imaging of lysis and leakage of single bacterium with 10-s temporal resolution. Movies are generated to visualize how the cell membrane was damaged by phage lysis, antibiotics attack, or dehydration, as well as the wall repair and cell recovery processes. The results show single-cell variations that are not obtainable from bulk measurements, confirming that CL microscopy of luciferase-expressing bacteria is a powerful tool for studying the fundamental biology of cells.

Survival and alteration of the plasmid-containing microorganism Escherichia coli Z905/pPHL7 introduced into manmade closed aquatic microcosms

It has been demonstrated that the transgenic microorganism Escherichia coli Z905/pPHL7 (AprLux+) can exist for a long time at an elevated concentration of mineral salts. The microorganism was introduced into microcosms with sterile brackish water (salinity variable from 21 to 22 g l-1) taken from Lake Shira (Khakasia, Russia). The survival of the microorganism was estimated both by measuring the growth of the colonies on solid nutrient media and by the bioluminescence exhibited by the transgenic strain in samples from the microcosms and in the enrichment culture with the added selective factor-ampicillin (50 micrograms/ml). In the enrichment culture, the bioluminescent signal was registered through the 160-day experiment. It has been shown that in the closed microcosms with brackish water the E. coli strain becomes heterogeneous in its ampicillin resistance. The populations of the transgenic strain were mainly represented by isolates able to persist in the medium containing 50 micrograms/ml, but there were also the cells (about 10%) with the threshold of ampicillin resistance not more than 0.05 micrograms/ml. Thus, it was shown that in the microcosms with brackish water and in the absence of the selective factor the transgenic strain survives and retails the recombinant plasmid.

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.

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.

Reporter gene vectors and assays

Gene reporter systems play a key role in gene expression and regulation studies. This review describes the ideal reporter systems, including reporter expression vector design. It summarizes the many uses of genetic reporters and outlines the currently available and commonly used reporter systems. Each system is described in terms of the reporter gene, the protein it encodes, and the assays available for detecting presence of the reporter. In addition, each reporter system is analyzed in terms of its recommended uses, advantages, and limitations.

Luciferase: a sensitive and quantitative probe for blood-brain barrier disruption

A novel method for quantitative analysis of blood-brain barrier (BBB) disruption is described, using luciferase as a probe in a murine model system. Purified luciferase was delivered to mouse brain by osmotic BBB disruption with hypertonic mannitol; control animals received an intracarotid inoculation of saline prior to infusion of luciferase. Delivery of luciferase to brain tissue was then assessed by enzyme assay of tissue extracts, and by immunohistochemical staining. Luciferase activity in the brain of mannitol-treated animals was found to be significantly elevated (approx. sevenfold), when compared to activity in control (saline-treated) mice. This finding was confirmed by quantitative immunohistochemical staining of tissue sections, using a luciferase-specific antibody. These studies showed that there was an eight-fold elevation in the level of extravascular luciferase particles within the brain of mannitol-treated animals, as compared to controls. Taken together these data show that purified recombinant luciferase can be used as a sensitive probe, with which to study the integrity of the BBB.

Visualizing gene expression in living mammals using a bioluminescent reporter

Control of gene expression often involves an interwoven set of regulatory processes. As information regarding regulatory pathways may be lost in ex vivo analyses, we used bioluminescence to monitor gene expression in living mammals. Viral promoters fused to firefly luciferase as transgenes in mice allowed external monitoring of gene expression both superficially and in deep tissues. In vivo bioluminescence was detectable using either intensified or cooled charge-coupled device cameras, and could be detected following both topical and systemic delivery of substrate. In vivo control of the promoter from the human immunodeficiency virus was demonstrated. As a model for DNA-based therapies and vaccines, in vivo transfection of a luciferase expression vector (SV-40 promoter and enhancer controlling expression) was detected. We conclude that gene regulation, DNA delivery and expression can now be noninvasively monitored in living mammals using a luciferase reporter. Thus, real-time, noninvasive study of gene expression in living animal models for human development and disease is possible.

Detection of baculovirus gene expression in insect cells and larvae by low light video image analysis

Recombinant baculovirus isolates BmNPVluc and AcNPVluc (Kopylova-Sviridova et al., 1990) expressing the luc gene in Bombyx mori N-4, and in Sf 9 and Trichoplusia ni 368 cells, respectively, were studied. Luc gene expression driven by baculovirus regulatory elements was detected by enzyme and photometric assays. The expression of recombinant AcNPVluc and BmNPVluc genes in infected larvae of the cabbage looper, T. ni and the tomato hornworm Manduca sexta was analyzed by low-light video image methods. Expression of the luc gene was detected at high levels in both the lepidopteran cells and in third to fifth instar T. ni larvae. However, no light emission was detected in M. sexta caterpillars. High levels of light emission were detected in T. ni larvae when occlusion bodies containing both wild type and recombinant virus were fed to larvae. The results of these experiments demonstrate that video image analysis can be used to monitor the progression of baculovirus infection in susceptible insect cells and larvae. Bioluminescence in recombinant virus infected larvae can be used to determine virus host range, to monitor latent virus infection in insect cells and to assess the spread of recombinant viruses in the environment. Video image analysis was found to be a sensitive method for rapid detection and semiquantitative measurement of luc gene expression in baculovirus infected cells and for monitoring virus infection in larval tissues.

Marker proteins for gene expression

Reporter genes are widely used as a rapid and convenient means of measuring molecular genetic events. Their role in experimental strategies has expanded from analysis of the DNA sequences mediating RNA transcription to the broader ensemble of molecular events that define phenotype expression. The several genetic reporters available today impart a range of performance criteria to choose from, including assay convenience and reliability, sensitivity, linearity, simplicity and dynamics.