Utility of firefly luciferase as a reporter gene for promoter activity in transgenic mice

Firefly Rats: Illuminating the Scientific Community in Transplantation Research

Fireflies produce light through luciferase-catalyzed reactions involving luciferin, oxygen, and adenosine triphosphate, distinct from other luminescent organisms. This unique feature has revolutionized molecular biology and physiology, serving as a valuable tool for cellular research. Luciferase-based bioluminescent imaging enabled the creation of transgenic animals, such as Firefly Rats. Firefly Rats, created in 2006, ubiquitously express luciferase and have become a critical asset in scientific investigations. These rats have significantly contributed to transplantation and tissue engineering studies. Their low immunogenicity reduces graft rejection risk, making them ideal for long-term tracking of organ/tissue/cellular engraftments. Importantly, in the islet transplantation setting, the ubiquitous luciferase expression in these rats does not alter islet morphology or function, ensuring accurate assessments of engrafted islets. Firefly Rats have illuminated the path of transplantation research worldwide for over a decade and continue accelerating scientific advancements in many fields.

Successful Genetic Transfection of the Colonic Protistan Parasite Blastocystis for Reliable Expression of Ectopic Genes

The microbial parasite Blastocystis colonizes the large intestines of numerous animal species and increasing evidence has linked Blastocystis infection to enteric diseases with signs and symptoms including abdominal pain, constipation, diarrhea, nausea, vomiting, and flatulence. It has also recently been reported to be an important member of the host intestinal microbiota. Despite significant advances in our understanding of Blastocystis cell biology and host-parasite interactions, a genetic modification tool is absent. In this study, we successfully established a robust gene delivery protocol for Blastocystis subtype 7 (ST7) and ectopic protein expression was further tested using a high sensitivity nano-luciferase (Nluc) reporter system, with promoter regions from several genes. Among them, a strong promoter encompassing a region upstream of the legumain 5' UTR was identified. Using this promoter combined with the legumain 3' UTR, which contains a conserved, precise polyadenylation signal, a robust transient transfection technique was established for the first time in Blastocystis. This system was validated by ectopic expression of proteins harbouring specific localization signals. The establishment of a robust, reproducible gene modification system for Blastocystis is a significant advance for Blastocystis research both in vitro and in vivo. This technique will spearhead further research to understand the parasite's biology, its role in health and disease, along with novel ways to combat the parasite.

Visualization of Protein Interactions in Living Cells Using Bimolecular Luminescence Complementation (BiLC)

The number of intracellular protein-protein interactions (PPIs) far exceeds the total number of proteins encoded by the genome. Dynamic cellular PPI networks respond to external stimuli and endogenous metabolism in order to maintain homeostasis. Many PPIs are directly involved in disease pathogenesis and/or resistance to therapeutics; they therefore represent potential drug targets. A technology generally termed 'bimolecular complementation' relies on the physical splitting of a molecular reporter (such as a fluorescent or luminescent protein) and fusion of the resulting two fragments to a pair of interacting proteins. When these proteins interact, they effectively reconstitute the activity of the molecular reporter (typically leading to increased fluorescence or luminescence). This unit describes the selection and development of bimolecular luminescence complementation (BiLC) assays for reporting intracellular PPIs, and provides examples in which BiLC was used to identify small molecules that can modulate PPIs. © 2017 by John Wiley & Sons, Inc.

Multiplex detection of protein-protein interactions using a next generation luciferase reporter

Cell-based assays of protein-protein interactions (PPIs) using split reporter proteins can be used to identify PPI agonists and antagonists. Generally, such assays measure one PPI at a time, and thus counterscreens for on-target activity must be run in parallel or at a subsequent stage; this increases both the cost and time during screening. Split luciferase systems offer advantages over those that use split fluorescent proteins (FPs). This is since split luciferase offers a greater signal:noise ratio and, unlike split FPs, the PPI can be reversed upon small molecule treatment. While multiplexed PPI assays using luciferase have been reported, they suffer from low signal:noise and require fairly complex spectral deconvolution during analysis. Furthermore, the luciferase enzymes used are large, which limits the range of PPIs that can be interrogated due to steric hindrance from the split luciferase fragments. Here, we report a multiplexed PPI assay based on split luciferases from Photinus pyralis (firefly luciferase, FLUC) and the deep-sea shrimp, Oplophorus gracilirostris (NanoLuc, NLUC). Specifically, we show that the binding of the p53 tumor suppressor to its two major negative regulators, MDM2 and MDM4, can be simultaneously measured within the same sample, without the requirement for complex filters or deconvolution. We provide chemical and genetic validation of this system using MDM2-targeted small molecules and mutagenesis, respectively. Combined with the superior signal:noise and smaller size of split NanoLuc, this multiplexed PPI assay format can be exploited to study the induction or disruption of pairwise interactions that are prominent in many cell signaling pathways.

Analysis of enamel development using murine model systems: approaches and limitations

A primary goal of enamel research is to understand and potentially treat or prevent enamel defects related to amelogenesis imperfecta (AI). Rodents are ideal models to assist our understanding of how enamel is formed because they are easily genetically modified, and their continuously erupting incisors display all stages of enamel development and mineralization. While numerous methods have been developed to generate and analyze genetically modified rodent enamel, it is crucial to understand the limitations and challenges associated with these methods in order to draw appropriate conclusions that can be applied translationally, to AI patient care. We have highlighted methods involved in generating and analyzing rodent enamel and potential approaches to overcoming limitations of these methods: (1) generating transgenic, knockout, and knockin mouse models, and (2) analyzing rodent enamel mineral density and functional properties (structure and mechanics) of mature enamel. There is a need for a standardized workflow to analyze enamel phenotypes in rodent models so that investigators can compare data from different studies. These methods include analyses of gene and protein expression, developing enamel histology, enamel pigment, degree of mineralization, enamel structure, and mechanical properties. Standardization of these methods with regard to stage of enamel development and sample preparation is crucial, and ideally investigators can use correlative and complementary techniques with the understanding that developing mouse enamel is dynamic and complex.

MRI-based detection of alkaline phosphatase gene reporter activity using a porphyrin solubility switch

The ability to map patterns of gene expression noninvasively in living animals could have impact in many areas of biology. Reporter systems compatible with MRI could be particularly valuable, but existing strategies tend to lack sensitivity or specificity. Here we address the challenge of MRI-based gene mapping using the reporter enzyme secreted alkaline phosphatase (SEAP), in conjunction with a water-soluble metalloporphyrin contrast agent. SEAP cleaves the porphyrin into an insoluble product that accumulates at sites of enzyme expression and can be visualized by MRI and optical absorbance. The contrast mechanism functions in vitro, in brain slices, and in animals. The system also provides the possibility of readout both in the living animal and by postmortem histology, and it notably does not require intracellular delivery of the contrast agent. The solubility switch mechanism used to detect SEAP could be adapted for imaging of additional reporter enzymes or endogenous targets.

Rapid identification of targeted transgene integrations in ES cells by fluorescence detection

The generation of transgenic animals with a gain-of-function mutation is commonly achieved by procedures based on random DNA integration. The resulting transgenic founder lines are unique, not reproducible and have variable expression patterns. In contrast, the targeted integration of transgenes into a predetermined neutral genomic position solves most of the inadequacies of random integration methods. However, homologous recombination (HR) in mouse embryonic stem cells (ESCs) currently requires careful design of the targeting vector and a laborious procedure to identify clones with the correct insertion event. Here, we introduce a feasible strategy that employs a heterozygous double fluorescent reporter ESC line for simple identification of a knock-in HR event via detection of endogenous fluorescence expression. Following positive selection using antibiotics, the system offers a second selection step to identify targeted clones by the loss of one of two fluorescence reporters in lieu of the time consuming Southern blotting and PCR analysis routinely applied in conventional targeting experiments. Moreover, the method allows for the simple detection of chimerism (negating the need for appropriate coat colour combinations) and enables the early detection of germline transmission by fluorescence reporter expression in F1 neonates.

Light-dependent and circadian transcription dynamics in vivo recorded with a destabilized luciferase reporter in Neurospora

We show that firefly luciferase is a stable protein when expressed at 25 °C in Neurospora, which limits its use as transcription reporter. We created a short-lived luciferase by fusing a PEST signal to its C-terminus (LUC-PEST) and applied the LUC-PEST reporter system to record in vivo transcription dynamics associated with the Neurospora circadian clock and its blue-light photosensory system over the course of several days. We show that the tool is suitable to faithfully monitor rapid, but also subtle changes in transcription in a medium to high throughput format.

Origins of cardiac fibroblasts

Cardiac fibroblasts play a critical role in maintenance of normal cardiac function. They are indispensable for damage control and tissue remodeling on myocardial injury and principal mediators of pathological cardiac remodeling and fibrosis. Despite their manyfold functions, cardiac fibroblasts remain poorly characterized in molecular terms. Evidence is evolving that cardiac fibroblasts are a heterogeneous population and likely derive from various distinct tissue niches in health and disease. Here, we review our emerging understanding of where cardiac fibroblasts come from, as well as how we can possibly use this knowledge to develop novel therapies for cardiac fibrosis.

The BCL-2 5' untranslated region contains an RNA G-quadruplex-forming motif that modulates protein expression

The BCL-2 gene encodes a 25 kDa membrane protein that plays critical roles in the control of apoptosis. The regulation of BCL-2 gene expression is highly complex and occurs both transcriptionally and posttranscriptionally. In particular, the 5' upstream region of BCL-2 contains a number of elements that control its expression. We have identified a highly conserved 25-nucleotide G-rich sequence (BCL2Q), with potential to fold into a RNA G-quadruplex structure, located 42 nucleotides upstream of the translation start site of human BCL-2. In this study, we used a series of biophysical experiments to show that the BCL2Q sequence folds into a stable RNA G-quadruplex in vitro, and we conducted functional luciferase reporter-based assays, in a cell-free lysate and in three types of human cell lines, to demonstrate that the BCL2Q sequence modulates protein expression in the context of the 493-nucleotide native 5' untranslated region of BCL-2.

An RNA G-quadruplex in the 5' UTR of the NRAS proto-oncogene modulates translation

Guanine-rich nucleic acid sequences can adopt noncanonical four-stranded secondary structures called guanine (G)-quadruplexes. Bioinformatics analysis suggests that G-quadruplex motifs are prevalent in genomes, which raises the need to elucidate their function. There is now evidence for the existence of DNA G-quadruplexes at telomeres with associated biological function. A recent hypothesis supports the notion that gene promoter elements contain DNA G-quadruplex motifs that control gene expression at the transcriptional level. We discovered a highly conserved, thermodynamically stable RNA G-quadruplex in the 5' untranslated region (UTR) of the gene transcript of the human NRAS proto-oncogene. Using a cell-free translation system coupled to a reporter gene assay, we have demonstrated that this NRAS RNA G-quadruplex modulates translation. This is the first example of translational repression by an RNA G-quadruplex. Bioinformatics analysis has revealed 2,922 other 5' UTR RNA G-quadruplex elements in the human genome. We propose that RNA G-quadruplexes in the 5' UTR modulate gene expression at the translational level.

cDNA cloning, expression and homology modeling of a luciferase from the firefly Lampyroidea maculata

The cDNA of a firefly luciferase from lantern mRNA of Lampyroidea maculata has been cloned, sequenced and functionally expressed. The cDNA has an open reading frame of 1647 bp and codes for a 548-residue-long polypeptide. Noteworthy, sequence comparison as well as homology modeling showed the highest degree of similarity with H. unmunsana and L. mingrelica luciferases, suggesting a close phylogenetic relationship despite the geographical distance separation. The deduced amino acid sequence of the luciferase gene of firefly L. maculata showed 93% identity to H. unmunsana. Superposition of the three-dimensional model of L. maculata luciferase (generated by homology modeling) and three dimensional structure of Photinus pyralis luciferase revealed that the spatial arrangements of Luciferin and ATP-binding residues are very similar. Putative signature of AMPbinding domain among the various firefly species and Lampyroidea maculata was compared and a striking similarity was found. Different motifs and sites have been identified in Lampyroidea maculata by sequence analysis. Expression and purification of luciferase from Lampyroidea maculata was carried out using Ni-NTA Sepharose. Bioluminescence emission spectrum was similar to Photinus pyralis luciferase.

An adenoviral vector for probing promoter activity in primary immune cells

Functional analysis of the DNA regulatory regions that control gene expression has largely been performed through transient transfection of promoter-reporter constructs into transformed cells. However, transformed cells are often poor models of primary cells. To directly analyze DNA regulatory regions in primary cells, we generated a novel adenoviral luciferase reporter vector, pShuttle-luciferase-GFP (pSLUG) that contains a promoterless luciferase cassette (with an upstream cloning site) for probing promoter activity, and a GFP expression cassette that allows for the identification of transduced cells. Recombinant adenoviruses generated from this vector can transduce a wide range of primary immune cells with high efficiency, including human macrophages, dendritic cells and T cells; and mouse T cells transgenic for the coxsackie and adenoviral receptor (CAR). In primary T cells, we show inducible nuclear factor of activated T cells (NF-AT) activity using a recombinant pSLUG adenovirus containing a consensus NF-AT promoter. We further show inducible IL-12/23 p40 promoter activity in primary macrophages and dendritic cells using a recombinant pSLUG adenovirus containing the proximal human IL-12/23 p40 promoter. The pSLUG system promises to be a powerful tool for the analysis of DNA regulatory regions in diverse types of primary immune cells.

A novel triple-modality reporter gene for whole-body fluorescent, bioluminescent, and nuclear noninvasive imaging

Two genetic reporter systems were developed for multimodality reporter gene imaging of different molecular-genetic processes using fluorescence, bioluminescence (BLI), and nuclear imaging techniques. The eGFP cDNA was fused at the N-terminus with HSV1-tk cDNA bearing a nuclear export signal from MAPKK (NES-HSV1-tk) or with truncation at the N-terminus of the first 45 amino acids (Delta45HSV1-tk) and with firefly luciferase at the C-terminus. A single fusion protein with three functional subunits is formed following transcription and translation from a single open reading frame. The NES-TGL (NES-TGL) or Delta45HSV1-tk/GFP/luciferase (Delta45-TGL) triple-fusion gene cDNAs were cloned into a MoMLV-based retrovirus, which was used for transduction of U87 human glioma cells. The integrity, fluorescence, bioluminescence, and enzymatic activity of the TGL reporter proteins were assessed in vitro. The predicted molecular weight of the fusion proteins (~130 kDa) was confirmed by western blot. The U87-NES-TGL and U87-Delta45-TGL cells had cytoplasmic green fluorescence. The in vitro BLI was 7- and 13-fold higher in U87-NES-TGL and U87-Delta45-TGL cells compared to nontransduced control cells. The Ki of (14)C-FIAU was 0.49+/-0.02, 0.51+/-0.03, and 0.003+/-0.001 ml/min/g in U87-NES-TGL, U87-Delta45-TGL, and wild-type U87 cells, respectively. Multimodality in vivo imaging studies were performed in nu/ nu mice bearing multiple s.c. xenografts established from U87-NES-TGL, U87-Delta45-TGL, and wild-type U87 cells. BLI was performed after administration of d-luciferin (150 mg/kg i.v.). Gamma camera or PET imaging was conducted at 2 h after i.v. administration of [(131)I]FIAU (7.4 MBq/animal) or [(124)I]FIAU (7.4 MBq/animal), respectively. Whole-body fluorescence imaging was performed in parallel with the BLI and radiotracer imaging studies. In vivo BLI and gamma camera imaging showed specific localization of luminescence and radioactivity to the TGL transduced xenografts with background levels of activity in the wild-type xenografts. Tissue sampling yielded values of 0.47%+/-0.08%, 0.86%+/-0.06%, and 0.03%+/-0.01%dose/g [(131)I]FIAU in U87-NES-TGL, U87-Delta45-TGL, and U87 xenografts, respectively. The TGL triple-fusion reporter gene preserves the functional activity of its subunits and is very effective for multimodality imaging. It provides for the seamless transition from fluorescence microscopy and FACS to whole-body bioluminescence imaging, to nuclear (PET, SPET, gamma camera) imaging, and back to in situ fluorescence image analysis.

Genomic structure of the luciferase gene and phylogenetic analysis in the Hotaria-group fireflies

The luminescent fireflies have species specific flash patterns, being recognized as sexual communication. The luciferase gene is the sole enzyme responsible for bioluminescence. We describe here the complete nucleotide sequence and the exon-intron structure of the luciferase gene of the Hotaria-group fireflies, H. unmunsana, H. papariensis and H. tsushimana. The luciferase gene of the Hotaria-group firefly including the known H. parvula spans 1950 bp and consisted of six introns and seven exons coding for 548 amino acid residues, suggesting highly conserved structure among the Hotaria-group fireflies. Although only one luciferase gene was cloned from H. papariensis, each of the two sequences of the gene was found in H. unmunsana (U1 and Uc) and H. tsushimana (T1 and T2). The amino acid sequence divergence among H. unmunsana, H. papariensis, and H. tsushimana only ranged from zero to three amino acid residues, but H. parvula differed by 10-11 amino acid residues from the other Hotaria-group fireflies, suggesting a divergent relationship of this species. Phylogenetic analysis using the deduced amino acid sequences of the luciferase gene resulted in a monophyletic group in the Hotaria excluding H. parvula, suggesting a close relationship among H. unmunsana, H. papariensis and H. tsushimana. Additionally, we also analyzed the mitochondrial cytochrome oxidase I (COI) gene of the Hotaria-group fireflies. The deduced amino acid sequence of the COI gene of H. unmunsana was identical to that of H. papariensis and H. tsushimana, but different by three positions from H. parvula. In terms of nucleotide sequences of the COI gene, intraspecific sequence divergence was sometimes larger than interspecies level, and phylogenetic analysis placed the three species into monophyletic groups unresolved among them, but excluded H. parvula. In conclusion, our results suggest that H. unmunsana, H. papariensis and H. tsushimana are very closely related or might be an identical species, at least based on the luciferase and COI genes.

Molecular cloning and expression of a cDNA encoding the luciferase from the firefly, Hotaria unmunsana

We have cloned and characterized a cDNA encoding the luciferase from the firefly, Hotaria unmunsana. The cDNA encoding the luciferase of H. unmunsana was isolated by RT-PCR with a gene-specific primer set. The cDNA encoding the luciferase of H. unmunsana is 1644 base pairs long with an open reading frame of 548 amino acid residues. The deduced amino acid sequence of the luciferase gene of H. unmunsana showed 98.0 and 96.8% identity to H. parvula and Luciola mingrelica, respectively. Phylogenetic analysis further confirmed that the deduced amino acid sequences of the H. unmunsana luciferase gene belonged to the same subfamily, Luciolinae. Southern blot analysis of genomic DNA suggested the presence of the H. unmunsana luciferase gene as a single copy and Northern blot analysis confirmed light organ-specific expression at the transcriptional level. The cDNA encoding the luciferase of H. unmunsana was expressed as a 61-kDa band in the baculovirus-infected insect cells and the extracts of the recombinant baculovirus-infected cells emitted luminescence in the luciferase activity assay.

Molecular cloning and expression of a cDNA encoding the luciferase from the firefly, Pyrocoelia rufa

To clone a cDNA encoding the luciferase of the firefly, Pyrocoelia rufa, we have constructed a cDNA library and isolated the luciferase gene using PCR with gene specific primers. Sequence analysis of the cDNA encoding the luciferase of P. rufa revealed that the 1647 bp cDNA has an open reading frame of 548 amino acid residues. The deduced amino acid sequences of the luciferase gene of P. rufa showed 98.9% homology to that of P. miyako. Phylogenetic analysis further confirmed the deduced amino acid sequences of the P. rufa luciferase gene belonged to the same subfamily, Lampyrinae. Southern blot analysis suggested possible presence of the P. rufa luciferase gene as a single copy and Northern blot analysis confirmed light organ-specific expression pattern at the transcriptional level. The cDNA encoding the luciferase of P. rufa was expressed as a 69 kDa band in baculovirus-infected insect cells and the recombinant baculovirus-infected cell extracts emitted luminescence in the luciferase activity assay.

The expression of the Photinus pyralis luciferase gene in Staphylococcus aureus Cowan I allows the development of a live amplifiable tool for immunodetection

We expressed the luc gene, encoding luciferase from Photinus pyralis, in Staphylococcus aureus Cowan I downstream of the plasmid-borne promoter for protein A. Constitutive luciferase synthesis did not impair the growth rate of the host nor did it affect the stability of the plasmid. Light production started immediately after addition of luciferin. The kinetic profile is of the glowing rather than the peak type. Because S. aureus Cowan I produces large quantities of protein A, of which a substantial part becomes covalently attached to rigid cell walls, the bacterial cells could be specifically immobilized on a substrate to which immunoglobulin G molecules were adsorbed either directly or as secondary antibodies. Light production from these cells can be used as a reporter tool for the detection of antigen-antibody complexes. Fourfold amplifications of the emitted signals were obtained by in situ incubation of the bound cells in bacterial growth medium.

Parameters affecting the use of the lac repressor system in eukaryotic cells and transgenic animals

Elements of the lactose operon were used to study parameters affecting gene expression in cultured cells and transgenic animals. A Lac repressor protein containing a nuclear transport signal was shown to inhibit expression of a reporter gene by interacting with lac operator sequences. In cultured cells, operator sequence, operator placement and induction parameters were all shown to be important for obtaining tight repression of a reporter gene followed by high level expression upon induction. Induction levels were also dependent on the reporter gene, with the luciferase gene yielding higher induction levels than the chloramphenicol acetyltransferase gene. In transgenic animals, the lacI mRNA was not detected in the C57BL/6 mouse strain until the animal was exposed to a demethylating agent. After 5-azacytidine treatment, expression of lacI mRNA was detected in the brain, heart, kidney, lung and ovary. In the FVB transgenic mouse strain, expression of lacI mRNA was detected without 5-azacytidine treatment in the kidney, liver, lung, and testes. Preliminary experiments with double transgenic animals containing both lacI and operator/luciferase transgenes showed a decrease in luciferase expression compared to the luciferase-only animals in both tissue extracts and transgenic fetal primary cultures, although IPTG induction was not achieved in these animals or primary cultures. The applicability and challenges of the system for regulation of gene expression are discussed.

Real time imaging of transcriptional activity in live mouse preimplantation embryos using a secreted luciferase

Study of gene expression kinetics during preimplantation mammalian development is difficult because of the limited amount of material and the usually destructive, static nature of molecular analyses. We describe continuous, noninvasive monitoring of gene expression in preimplantation embryos by using a secreted luminescent reporter, Vargula luciferase. Transgene expression profiles were followed by assaying aliquots of culture medium or by direct visualization of Vargula luciferase secretion from living embryos in real time through photon imaging. With this approach, it is possible to observe epigenetic modulations of gene expression and to link this over time to the developmental capacity of individual embryos. In addition, by developing a strategy where expression from integrated transgenes is enhanced relative to that from nonintegrated DNA, we provide evidence that rapid detection of transgene integration prior to the blastocyst stage should be possible. Thus, imaging of Vargula luciferase secretion may also be useful in the early screening of embryos, for example, in the production of transgenic livestock.

A luciferase expression system for Physarum that facilitates analysis of regulatory elements

We have developed a transient expression system for the protist Physarum polycephalum based on firefly luciferase. We demonstrate the utility of this system for comparing the activities of different promoters in Physarum amoebae, and also for detecting genetic elements that affect the level of gene expression. This system is likely to facilitate improvements in the stable transformation of this organism.

Reporter genes in transgenic mice

Although in vivo models utilizing endogenous reporter genes have been exploited for many years, the use of reporter transgenes to dissect biological issues in transgenic animals has been a relatively recent development. These transgenes are often, but not always, of prokaryotic origin and encode products not normally associated with eukaryotic cells and tissues. Some encode enzymes whose activities are detected in cell and tissue homogenates, whereas others encode products that can be detected in situ at the single cell level. Reporter genes have been used to identify regulatory elements that are important for tissue-specific gene expression or for development; they have been used to produce in vivo models of cancer; they have been employed for the study of in vivo mutagenesis; and they have been used as a tool in lineage analysis and for marking cells in transplantation experiments. The most commonly used in situ reporter gene is lacZ, which encodes a bacterial beta-galactosidase, a sensitive histochemical marker. Although it has been used with striking success in cultured cells and in transgenic mouse embryos, its postnatal in vivo expression has been unreliable and disappointing. Nevertheless, the ability to express reporter genes in transgenic mice has been an invaluable resource, providing insights into in vivo biological mechanisms. The development of new in vivo models, such as those in which expression of transgenes can be activated or repressed, should produce transgenic animal systems that extend our capacity to address heretofore unresolved biological questions.

Micromachined electroporation system for transgenic fish

Luciferase gene was introduced into fertilized eggs of medaka by a localized electric field between thin film electrodes formed on a glass plate. Miniaturization of the electrodes enabled us to apply a localized electric field to the animal pole of the fertilized egg. Biochemical luminescence and an electrophoresis pattern showed expression and integration of the gene, respectively. The presented system had a higher ratio of gene introduction than the conventional electroporation method.

Major approaches for generating and analyzing transgenic mice. An overview

Over the past decade, the development of gene-transfer technology in whole animals has afforded unprecedented opportunities for investigators to probe complex regulatory systems in vivo. Important advances in our understanding of the mechanisms of gene expression and regulation and the development of animal models of human diseases are but two examples of how this technology has affected medical science. Transgenic animals are defined as animals in which a segment of DNA has been physically integrated into the genome of all cells, including the germ line, so that it can be transmitted to offspring as a simple Mendelian trait. The DNA segment generally consists of a whole cloned gene, cDNA, or a novel gene modified by recombinant DNA methodologies. Whole genomic clones of genes are often used to study tissue- and cell-specific expression and regulation or can be used to overexpress a gene product. Alternatively, the coding region of one gene can be fused to the transcriptional regulatory region of another gene, causing it to be expressed in a new spectrum of tissues and cell types. A number of methods can be used to introduce the DNA segment, including direct microinjection of one-cell fertilized embryos, retroviral-mediated transfer, or gene transfer in embryonic stem cells. The technique most often used to generate transgenic animals and perform "gene addition" experiments is direct microinjection. Alternatively, gene deletions or "knockouts" are performed by gene transfer in embryonic stem cells by specifically targeting the site of integration in the genome.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapid assessment of drug susceptibilities of Mycobacterium tuberculosis by means of luciferase reporter phages

Effective chemotherapy of tuberculosis requires rapid assessment of drug sensitivity because of the emergence of multidrug-resistant Mycobacterium tuberculosis. Drug susceptibility was assessed by a simple method based on the efficient production of photons by viable mycobacteria infected with specific reporter phages expressing the firefly luciferase gene. Light production was dependent on phage infection, expression of the luciferase gene, and the level of cellular adenosine triphosphate. Signals could be detected within minutes after infection of virulent M. tuberculosis with reporter phages. Culture of conventional strains with antituberculosis drugs, including isoniazid or rifampicin, resulted in extinction of light production. In contrast, light signals after luciferase reporter phage infection of drug-resistant strains continued to be produced. Luciferase reporter phages may help to reduce the time required for establishing antibiotic sensitivity of M. tuberculosis strains from weeks to days and to accelerate screening for new antituberculosis drugs.

Enhancement of firefly luciferase activity by cytidine nucleotides

The temporal pattern of light production by firefly luciferase depends on the ATP concentration. With low concentrations of ATP a constant production of light occurred while at high concentrations of ATP (greater than 10 microM) there was a flash of light followed by a decline in light production. This time course of light production with high ATP concentrations was changed from the flash pattern to a pattern with a constant production of light by several cytidine nucleotides. CTP, CDP, dCTP, dCDP, dideoxyCTP, periodate-oxidized CTP and CDP, and the etheno derivatives of CTP and CDP produced that change. CMP, cytidine, CDP-glycerol, CDP-glucose, CDP-ethanolamine, and benzoylbenzoylCTP either were inhibitory to firefly luciferase or were not effective in changing the flash time course. Coenzyme A and related compounds also changed the time course of light production. The changes in time course produced by either cytidine nucleotides or CoA were inhibited by desulfoCoA. These compounds apparently enhanced light production by promoting the dissociation of the inhibitory product, oxidized luciferin, from the enzyme. When the activating compounds were used with high concentrations of ATP, the sensitivity of assay for firefly luciferase was increased. This increased sensitivity is important when using the firefly luciferase gene as a reporter.

Avian retroviral expression of luciferase

Biologically active replication-competent (subgroups A, B, and C) and replication-defective Rous sarcoma virus-derived vectors containing the cDNA encoding firefly luciferase as a reporter gene were constructed. In these retroviral vectors, luciferase is expressed from a spliced subgenomic mRNA. A biologically active replication-defective UR2 virus-derived vector expressing the reporter gene as a gag-luciferase fusion protein from an unspliced genomic mRNA was also constructed. The luciferase reporter gene was used because it lacks homology with chicken genomic sequences and because a rapid and sensitive direct enzymatic assay is available to monitor luciferase expression in retrovirus-infected cells. The levels of luciferase expression in luciferase recombinant retrovirus-infected chicken embryo fibroblasts are greater than 10(3) higher than that detected in uninfected cells or in cells infected with retroviral vectors carrying other genes. Endpoint dilution titration experiments demonstrated that one infected cell can be detected in a background of 10(3) uninfected cells. The vectors are stable in tissue culture and high level expression of the unselected luciferase reporter gene is maintained. The vectors were used to express luciferase in chicken embryos, demonstrating the potential utility of luciferase as a reporter in vivo.

Membrane-permeable luciferin esters for assay of firefly luciferase in live intact cells

Five esters of luciferin were synthesized and compared with native luciferin as substrates for firefly luciferase expressed in live intact mammalian cells. The esters themselves were not substrates for purified luciferase, but four were substrates for a purified esterase and all appeared to be hydrolysed to luciferin within mammalian cells. At a substrate concentration of 0.01 mM, the peak luminescence from the cos cells expressing luciferase was up to 6-fold greater with the esters than with unmodified luciferin. At 0.1 mM, the difference between luciferin and the esters was decreased. The kinetics of the luminescent signal with the different luciferin esters varied significantly, indicating possible differences in the rates of uptake, breakdown and enzyme inhibition. The esters did not support luminescence from Escherichia coli cells expressing firefly luciferase, suggesting a lack of appropriate esterase activity in this particular strain. The esters could be useful for the assay of luciferase expression in intact mammalian cells when luciferin levels are limiting, for example in tissues, and in plants. Alternative luciferin derivatives may allow further improvements in sensitivity.

From Luc and Phot genes to the hospital bed

The Luc gene from the firefly Photinus pyralis has been isolated by cloning it in pcDV1 PL plasmid primer and Honjo linker and the Phot gene isolated from Aequorea victoria using the polymerase chain reaction. A method has been established using SP6 RNA polymerase for transcribing and translating bioluminescent genes in vitro. It should now be possible to engineer these genes to measure intracellular ATP and the covalent modification of proteins in single, live cells, providing unique insights into the molecular basis of disease.

Introduction to beetle luciferases and their applications

All beetle luciferases have evolved from a common ancestor: they all use ATP, O2, and a common luciferin as substrates. The most studied of these luciferases is that derived from the firefly Photinus pyralis, a beetle in the superfamily of Cantharoidea. The sensitivity with which the activity of this enzyme can be assayed has made it useful in the measurement of minute concentrations of ATP. With the cloning of the cDNA coding this luciferase, it has also found wide application in molecular biology as a reporter gene. We have recently cloned other cDNAs that code for luciferases from the bioluminescent click beetle, Pyrophorus plagiophthalamus, in the superfamily Elateroidea. These newly acquired luciferases are of at least four different types, distinguishable by their ability to emit different colours of bioluminescence ranging from green to orange. Unique properties of these luciferases, especially their emission of multiple colours, may make them additionally useful in applications.

Complementary DNA coding click beetle luciferases can elicit bioluminescence of different colors

Eleven complementary DNA (cDNA) clones were generated from messenger RNA isolated from abdominal light organs of the bioluminescent click beetle, Pyrophorus plagiophthalamus. When expressed in Escherichia coli, these clones can elicit bioluminescence that is readily visible. The clones code for luciferases of four types, distinguished by the colors of bioluminescence they catalyze: green (546 nanometers), yellow-green (560 nanometers), yellow (578 nanometers), and orange (593 nanometers). The amino acid sequences of the different luciferases are 95 to 99 percent identical with each other, but are only 48 percent identical with the sequence of firefly luciferase (Photinus pyralis). Because of the different colors, these clones may be useful in experiments in which multiple reporter genes are needed.

Firefly luciferase as a tool in molecular and cell biology

The unique properties of firefly luciferase and the cloning of the gene for this enzyme have spawned a number of novel applications of this protein. We summarize a few of these applications including its use as a reporter gene, as a model for the study of protein import into peroxisomes, and as a component of a heterologous gene expression system.