Fission yeast mal2+ is required for chromosome segregation

By a screen designed to isolate new fission yeast genes required for chromosome segregation, we have identified mal2+. The conditionally lethal mal2-1 allele gives rise to increased loss of a nonessential minichromosome at the permissive temperature and leads to severe missegregation of the chromosomes at the nonpermissive temperature. Cloning by complementation and subsequent sequence analysis revealed that mal2 is a novel protein with a mass of 34 kDa. Cells containing a mal2 null allele were inviable, indicating that mal2+ is an essential gene. Fusion of mal2 protein to the green fluorescent protein (GFP) showed that mal2 was predominantly localized in the nucleus. Sensitivity to microtubule-destabilizing drugs and strong genetic interactions with alpha1-tubulin suggest an interaction of the mal2 protein with the microtubule system. Spindle formation and elongation were not detectably affected in the mal2-1 mutant as determined by indirect immunofluorescence. However, anomalous chromosome movement on the spindle leading to aberrant distribution of the chromosomal material was observed.

An improved green fluorescent protein gene as a vital marker in plants

A synthetic green fluorescent protein (GFP) gene (pgfp) was constructed to improve GFP expression in plants. Corn and tobacco protoplast transient assays showed that pgfp gave about 20-fold brighter fluorescence than the wild-type gene (gfp). Replacement of the serine at position 65 with a threonine (S65Tpgfp) or a cysteine (S65Cpgfp) yielded 100- to 120-fold brighter fluorescence than wild-type gfp upon excitation with 490-nm light. Incorporation of a plant intron into the coding region yielded an additional 1.4-fold improvement, for a cumulative improvement of about 150-fold in fluorescence at 490-nm excitation. Various versions of pgfp were also stably introduced into corn, wheat, tobacco, and Arabidopsis plants. Bright-green fluorescence was observed with a fluorescence microscope in virtually all examined tissues of transgenic monocots and dicots. In the case of Arabidopsis, expression of the pgfp gene under the enhanced 355 promoter of the cauliflower mosaic virus produced green fluorescence that was readily detectable by eye using a hand-held, long-wave ultraviolet lamp and/or a black-light source.

Green fluorescent protein (GFP) as a new vital marker in the phytopathogenic fungus Ustilago maydis

Pathogenic development of Ustilago maydis, the causative agent of corn smut disease, is a multistep process. Compatible yeast-like cells fuse and this generates the infectious dikaryon which grows filamentously. Having entered the plant the dikaryon induces tumors in its host in which massive proliferation of fungal material, karyogamy and spore formation occur. In order to follow fungal development from the initial steps to the final stage we have expressed the green fluorescent protein (GFP) from Aequorea victoria as a vital marker in U. maydis and demonstrate that GFP-tagged strains can be used to study host-pathogen interactions in vivo.

Use of virion DNA as a cloning vector for the construction of mutant and recombinant herpesviruses

We have developed improved procedures for the isolation of deletion mutant, point mutant, and recombinant herpesvirus saimiri. These procedures take advantage of the absence of NotI and AscI restriction enzyme sites within the viral genome and use reporter genes for the identification of recombinant viruses. Genes for secreted engineered alkaline phosphatase and green fluorescent protein were placed under simian virus 40 early promoter control and flanked by NotI and AscI restriction sites. When permissive cells were cotransfected with herpesvirus saimiri virion DNA and one of the engineered reporter genes cloned within herpesvirus saimiri sequences, recombinant viruses were readily identified and purified on the basis of expression of the reporter gene. Digestion of recombinant virion DNA with NotI or AscI was used to delete the reporter gene from the recombinant herpesvirus saimiri. Replacement of the reporter gene can be achieved by NotI or AscI digestion of virion DNA and ligation with a terminally matched fragment or, alternatively, by homologous recombination in cotransfected cells. Any gene can, in theory, be cloned directly into the virion DNA when flanked by the appropriate NotI or AscI sites. These procedures should be widely applicable in their general form to most or all herpesviruses that replicate permissively in cultured cells.

Green fluorescent protein expressed in living mosquitoes--without the requirement of transformation

Mosquitoes transmit viruses, protozoa and nematodes that are major causes of morbidity and mortality in humans. Details of arthropod anatomy and development, and the replication and development of pathogens in the arthropod vector, have relied upon examination of dissected or histologically processed material. We constructed a double-subgenomic Sindbis (dsSIN) virus expressing green fluorescent protein to demonstrate the potential of this protein for studying pathogen development in living arthropods. We were able to observe dissemination of virus, and furthermore, it was possible to observe components of the nervous system of mosquito larvae in extraordinary detail and record this on video tape. Although green fluorescent protein has been used as a reporter gene in a number of organisms, expression has relied upon transformation of cells or embryos. Transformation technology has limited applicability, thus we have described an alternative system that, due to the broad host range and viral tropisms of dsSIN viruses, may be useful to scientists in a range of disciplines. Green fluorescent protein may also provide a non-lethal selection method for use in transgenic arthropod research.

Mutations in a cyclic nucleotide-gated channel lead to abnormal thermosensation and chemosensation in C. elegans

The C. elegans tax-4 mutants are abnormal in multiple sensory behaviors: they fail to respond to temperature or to water-soluble or volatile chemical attractants. We show that the predicted tax-4 gene product is highly homologous to vertebrate cyclic nucleotide-gated channels. Tax-4 protein expressed in cultured cells functions as a cyclic nucleotide-gated channel. The green fluorescent protein (GFP)-tagged functional Tax-4 protein is expressed in thermosensory, gustatory, and olfactory neurons mediating all the sensory behaviors affected by the tax-4 mutations. The Tax-4::GFP fusion is partly localized at the sensory endings of these neurons. The results suggest that a cyclic nucleotide-gated channel is required for thermosensation and chemosensation and that cGMP is an important intracellular messenger in C. elegans sensory transduction.

Chemosensory neurons function in parallel to mediate a pheromone response in C. elegans

Formation of the C. elegans dauer larva is repressed by the chemosensory neurons ADF, ASI, and ASG. Mutant analysis has defined two parallel genetic pathways that control dauer formation. By killing neurons in these mutants, we show that mutations in one of these genetic pathways disrupt dauer repression by ADF, ASI, and ASG. One gene in this pathway is daf-7, which encodes a TGFbeta-related protein. We find that daf-7::GFP fusions are expressed specifically in ASI and that expression is regulated by dauer-inducing sensory stimuli. We also show that a different chemosensory neuron, ASJ, functions in parallel to these neurons to induce dauer formation. Mutations in the second genetic pathway activate dauer formation in an ASJ-dependent manner. Thus, the genetic redundancy in this process is reflected at the neuronal level.

Secretion of green fluorescent protein from recombinant baculovirus-infected insect cells

Trichoplusia ni (High Five) and Spodoptera frugiperda (Sf21) cells were engineered for expression of epitope (Flag)-tagged signal peptide-green fluorescent protein (GFP) fusions to examine the suitability of GFP as a secretory marker. The recombinant baculovirus-infected cells became fluorescent, and the High Five cells but not Sf21 cells secreted GFP in the culture medium as detected by the presence in the culture supernatant of a Flag-immunoreactive 30-kDa species and the characteristic 510-nm GFP fluorescence peak. Signal peptides derived from ecdysteroid UDP-glucosyltransferase of Autographa californica nuclear polyhedrosis virus and from rat brain glutamate receptor were both able to promote secretion of GFP. GFP may thus be used as a research tool in the study of the secretory process in insect cells both in cell biology and in biotechnological applications.

Quantitative analysis of transient gene expression in mammalian cells using the green fluorescent protein

The green fluorescent protein (Gfp) has been used as a reporter, along with flow cytometric analysis, to follow the dynamics of gene expression in transiently transfected mammalian cells. Gene transfer conditions for lipofection were optimized. The highest fraction of transfectants were obtained when lipid-DNA complexes were formed with 6 microliters lipid and 1 microgram DNA for chinese hamster ovary (CHO) cells and with 9 microliters lipid and 2 micrograms DNA for NIH/3T3 cells. Chinese hamster ovary cells were monitored for Gfp expression and growth for 6 days following transfection. An initial decrease in viability for 36 h was observed after which cell growth followed exponential kinetics with increasing viability. Intracellular accumulation of recombinant protein peaked at 24 h post-transfection and then decreased with first order kinetics at a rate comparable to the specific growth rate. It appears that dilution by growth accounts for the decrease of Gfp in the biomass. Immunofluorescent staining of Gfp and subsequent flow cytometric analysis of transfected cells revealed a linear correlation between the green fluorescence and immunofluorescence. This indicates that green fluorescence is a quantitative measure of intracellular Gfp in single cells in spite of the dynamics of post-translational modifications involved in the conversion of expressed protein into its fluorescent form. A structured model has been formulated to describe the observed kinetics of gene expression and fluorophore formation. The model accurately predicts experimental trends and suggests that the fraction of non-fluorescent Gfp is significant only during the initial period of gene expression.

Intracellular targeting and mRNA interactions of the eukaryotic translation initiation factor eIF4E in the yeast Saccharomyces cerevisiae

The 5' cap structure of eukaryotic mRNAs is believed to play a role in a number of cellular processes, including pre-mRNA splicing, nuclear export and translation. An essential cap-binding protein that is likely to mediate the participation of the cap in at least one of these processes is the eukaryotic translation initiation factor eIF4E. This protein is thought to facilitate the initial ribosomal interaction with the 5' end of the mRNA, involving the binding of eIF4E to the cap in the cytoplasm. Yet the subcellular distribution and mechanism of targeting of eIF4E has been an unresolved issue. We have therefore examined whether eIF4E in the yeast Saccharomyces cerevisiae is directed to the nucleus by virtue of a nuclear localization sequence (NLS) in its amino acid sequence. eIF4E was fused with the "marker proteins' yeast invertase and jellyfish green fluorescent protein. The distribution of these fusions could be followed using immunofluorescence and confocal microscopy of protoplasts and whole cells. These and other fusions were used to show that while yeast eIF4E does not possess an efficiently functioning NLS, it can be transported into the nucleus if provided with a known active NLS. However, an NLS-eIF4E fusion of this type cannot be stably supported by the cell, most likely because of its inhibitory effects when present in large quantities in the nucleus, whereas an NLS fusion with a mutant form of eIF4E that has reduced cap-affinity is tolerated.

Modification of phytohormone response by a peptide encoded by ENOD40 of legumes and a nonlegume

The gene ENOD40 is expressed during early stages of legume nodule development. A homolog was isolated from tobacco, which, as does ENOD40 from legumes, encodes an oligopeptide of about 10 amino acids. In tobacco protoplasts, these peptides change the response to auxin at concentrations as low as 10(-12) to 10(-16)M. The peptides encoded by ENOD40 appear to act as plant growth regulators.

Upregulation of the APC gene product during neuronal differentiation of rat pheochromocytoma PC12 cells

The adenomatous polyposis coli (APC) gene, the mutation of which is responsible for familial adenomatous polyposis and sporadic colorectal tumors, is highly expressed in the central nervous system. To elucidate the contribution of the APC protein to neuronal differentiation, changes in APC expression were examined during nerve growth factor (NGF)-induced differentiation of rat pheochromocytoma PC12 cells. The expression of APC gradually increased throughout the time course, in particular it increased markedly after 7 days of exposure to NGF. However, forced expression of APC did not induce neuronal differentiation of PC12 cells. These results suggest that the APC protein itself does not have the potential to induce neuronal differentiation, but rather is upregulated secondary to the differentiation of PC12 cells.

Highly efficient production of GFP and its derivatives in insect cells for visual in vitro applications

We have generated recombinant baculoviruses for expression of the green fluorescent protein (GFP), a bright GFP mutant (S65T), and a GFP-streptavidin fusion protein in Sf9 and High Five insect cell lines. At 3-4 days post infection, about 30% of the total protein contents was represented by the recombinant protein products, giving the infected insect cells a bright green color which was clearly visible by eye in daylight. The isolated GFP-streptavidin fusion protein, which possessed fluorescence properties identical to those of the native GFP, was capable of binding biotin as shown by using biotinylated beads as well as biotinylated antibody complexes decorating surface expressed GluR-6 glutamate receptor in live and fixed insect cells. The exceptionally high expression levels of GFP and GFP (S65T) and the GFP-streptavidin fusion protein in recombinant baculovirus infected insects should facilitate production of GFP derivatives for in vitro applications.

A tissue-specific repressor in the sea urchin embryo of Lytechinus pictus binds the distal G-string element in the LpS1-beta promoter

LpS1 RNA transcripts and proteins are expressed exclusively in the aboral ectoderm of the embryo in the sea urchin Lytechinus pictus. We have characterized the LpS1-beta promoter to identify the cis-acting elements that may be involved in the aboral ectoderm-specific expression of the LpS1-beta gene. The distal G-string site, composed of six contiguous guanine deoxynucleotides located at -721 to -726, was analyzed. A mutation at the distal G-string caused over a two-fold increase in reporter chloramphenicol acetyltransferase gene activity and inappropriate expression of reporter green fluorescent protein in nonaboral ectoderm cells in L. pictus embryos. These results suggest that the proteins that bind the distal G-string act as a spatial repressor in the nonaboral ectoderm cells of the developing embryo.

Subcellular imaging of intramitochondrial Ca2+ with recombinant targeted aequorin: significance for the regulation of pyruvate dehydrogenase activity

Specific targeting of the recombinant, Ca2+ -sensitive photoprotein, aequorin to intracellular organelles has provided new insights into the mechanisms of intracellular Ca2+ homeostasis. When applied to small mammalian cells, a major limitation of this technique has been the need to average the signal over a large number of cells. This prevents the identification of inter- or intracellular heterogeneities. Here we describe the imaging in single mammalian cells (CHO.T) of [Ca2+] with recombinant chimeric aequorin targeted to mitochondria. This was achieved by optimizing expression of the protein through intranuclear injection of cDNA and through the use of a charge-coupled device camera fitted with a dual microchannel plate intensifier. This approach allows accurate quantitation of the kinetics and extent of the large changes in mitochondrial matrix [Ca2+] ([Ca2+](m)) that follow receptor stimulation and reveal different behaviors of mitochondrial populations within individual cells. The technique is compared with measurements of [Ca2+](m) using the fluorescent indicator, rhod2. Comparison of [Ca2+](m) with the activity of the Ca2+ -sensitive matrix enzyme, pyruvate dehydrogenase (PDH), reveals that this enzyme is a target of the matrix [Ca2+] changes. Peak [Ca2+](m) values following receptor stimulation are in excess of those necessary for full activation of PDH in situ, but may be necessary for the activation of other mitochondrial dehydrogenases. Finally, the data suggest that the complex regulation of PDH activity by a phosphorylation-dephosphorylation cycle may provide a means by which changes in the frequency of cytosolic (and hence mitochondrial) [Ca2+] oscillations can be decoded by mitochondria.

The utility of fluorescent in vivo reporter genes in molecular cardiology

In vivo reporter genes can be used in different ways in molecular cardiology. In this paper studies are presented using the green fluorescent protein and one of its mutants, S65T-GFP, as in vivo reporter genes. With this new molecular tool we studied cell type specificity of the murine ventricular myosin light chain 2 promoter, positive cell identification prior to patch clamp procedures, and the use of fluorescence activated cell sorting of transiently transfected mammalian cells.

Movement of yeast cortical actin cytoskeleton visualized in vivo

Fusion proteins between the green fluorescent protein (GFP) and the cytoskeleton proteins Act1p (actin), Sac6p (yeast fimbrin homolog), and Abp1p in budding yeast (Saccharomyces cerevisiae) localize to the cortical actin patches. The actin fusions could not function as the sole actin source in yeast, but fusions between the actin-binding proteins Abp1p and Sac6p complement fully the phenotypes associated with their gene deletions. Direct observation in vivo reveals that the actin cortical patches move. Movement of actin patches is constrained to the asymmetric distribution of the patches in growing cells, and this movement is greatly reduced when metabolic inhibitors such as sodium azide are added. Fusion protein-labeled patches are normally distributed during the yeast cell cycle and during mating. In vivo observation made possible the visualization of actin patches during sporulation as well.

Effect of the ATP level on the overall protein biosynthesis rate in a wheat germ cell-free system

A sensitive assay which examines the effects of ATP level on the overall activity of a cell-free translation system in a protein synthesis is described. The translational activity of cell-free system was measured in terms of a rate of protein synthesis directed by the 'test' template. The test template encodes a photoluminescent protein, obelin accumulation was determined from the kinetic curves of obelin. The rate of obelin mRNA translation. Time-dependent nucleotide level measurements were conducted throughout the translation processes. It has been shown that the rate of translation decreases exponentially with the decrease of the ATP level. This fall in the overall translation rate is due in part to the mRNA becoming inactive in the translation process. This is not caused by degradation, this mRNA can be restored for translation in a fresh cell-free system by phenol treatment. The reported results provide evidence that the level of ATP unambiguously determines the translational activity of the system.

Construction of a fusion protein between protein A and green fluorescent protein and its application to western blotting

Aequorea green fluorescent protein (GFP) and protein A were fused and expressed in Escherichia coli. The fluorescent native fusion protein (PA-GFP) migrated at 47 kDa in SDS-PAGE. However, the non-fluorescent denatured PA-GFP migrated at 57 kDa which corresponds to the theoretical molecular mass. Although the reason(s) for this mobility shift between fluorescent and non-fluorescent molecules remains unclear, the small ring structure within the native molecules may affect their mobility. The cell extract, prepared from an E. coli strain producing PA-GFP, was used in Western and dot blots. The sensitivity and specificity of the PA-GFP detection were sufficient for rapid and easy screening.

Use of the green fluorescent protein as a marker in transfected Leishmania

We have tested the suitability of the green fluorescent protein (GFP) of Aequorea victoria as a marker for studies of gene expression and protein targeting in the trypanosomatid parasite Leishmania. Leishmania promastigotes expressing GFP from episomal pXG vectors showed a bright green fluorescence distributed throughout the cell, readily distinguishable from control parasites. Transfection of a modified GFP gene containing GC-rich synonymous codons and the S65T mutation (GFP+) yielded a much higher fluorescence. FACS analysis revealed a clear quantitative separation between GFP-transfected and control parasites, with pXG-GFP+ transfectants showing fluorescence signals more than 100-fold background. Episomal DNAs could be recovered from small numbers of fixed cells, showing that GFP could be used as a convenient screenable marker for FACS separations. GFP was fused to the C-terminus of the LPG1 protein, which retained its ability to restore LPG expression when expressed in the lpg- R2D2 mutant of L. donovani. The LPG1(GFP) fusion was localized to a region situated between the nucleus and kinetoplast; its pattern was similar to that of LPG2, which is known to be located in the Golgi apparatus. This is notable as LPG1 participates in the biosynthesis of the glycan core of the LPG GPI anchor, whereas protein GPI anchor biosynthesis occurs in the endoplasmic reticulum. These studies suggest that the GFP will be a broadly useful marker in Leishmania.

Mitochondrial alterations induced by aspirin in rat hepatocytes expressing mitochondrially targeted green fluorescent protein (mtGFP)

Mitochondria in primary living hepatocytes were visualized in cells transfected with a chimeric plasmid encoding for the green fluorescent protein (GFP) of Aequorea victoria engineered to be specifically targeted to mitochondria, as described recently (Rizutto et al. (1995) Curr. Biol. 5, 635-642). The identification of the fluorescent organelles as authentic mitochondria was confirmed by double labeling with rhodamine 123. Acetylsalicylate treatment of hepatocytes induced in mitochondria typical morphological alterations closely analogous to the swelling promoted by acetylsalicylate in isolated mitochondria. Cyclosporin A, which in isolated mitochondria prevents the changes induced by acetylsalicylate, had no protective action but induced per se specific alterations in the morphology of mitochondria. Moreover, exposure of hepatocytes to cyclosporin A followed by acetylsalicylate caused the same mitochondrial changes induced by each of the two compounds separately. The structural alterations caused by acetylsalicylate were constantly associated with a decrease in mitochondrial urea synthesis and cell viability.

Functional expression of the Aequorea victoria green fluorescent protein in insect cells using the baculovirus expression system

A DNA fragment encoding the green fluorescent protein (GFP) was isolated via PCR from a jellyfish Aequorea victoria cDNA, cloned and sequenced. Subsequently, a recombinant baculovirus bearing the coding region of the GFP under the transcriptional control of the Autographa californica nuclear polyhedrosis virus (AcMNPV) polyhedrin gene promoter was constructed and isolated. High-level expression of GFP could be easily monitored in Spodoptera frugiperda (Sf9) insect cells after infection with recombinant baculovirus, due to the intrinsic fluorescence (lambda(max) = 508 nm) of the recombinant protein after excitation with blue light (lambda(max) = 400 nm). The functional recombinant GFP displayed an apparent molecular mass of approximately 43 kDa and the fluorescence emission spectrum of the recombinant protein was virtually identical to that of the native green fluorescent protein.

Agonist-stimulated free calcium in subcellular compartments. Delivery of recombinant aequorin to organelles using a replication deficient adenovirus vector

Changes in the concentration of calcium ions ([Ca2+]) within cellular organelles play a central role in controlling cellular function. We have engineered the Ca2+ sensitive photoprotein aequorin to monitor selectively [Ca2+] within defined subcellular compartments, namely the cytosol, nucleus and endoplasmic reticulum. DNA encoding the engineered aequorins have been inserted into a replication deficient adenovirus (Ad) type 5 E1-vector, under control of the cytomegalovirus (CMV) major immediate early promoter. The Ad vector provides a simple and efficient method to express the photoproteins in a wide variety of mammalian cell types. Efficient targeting of the photoproteins to the appropriate cellular compartment was established immunocytochemically in COS7 cells, where it was expressed in up to 100% of the target population. Levels of expression could be controlled by virus dose and chemical agents which affect the activity of the CMV promoter. In HeLa cells expressing nuclear targeted aequorin or cytosolic aequorin, ATP or histamine induced immediate biphasic elevations of both nuclear and cytosolic [Ca2+]; subsequent challenge with agonist evoked similar responses. In addition to epithelial type adherent cell lines (COS7 and HeLa), aequorin expression was also readily detected in non-adherent cells of myeloid lineage (K562 and HL60) and non-adherent primary cells polymorphonuclear leucocytes (neutrophils). The Ad vectors can, therefore, be used to express targeted aequorin in a range of different cell types and represents a novel method to monitor changes in free [Ca2+] in cellular organelles.

A rapid and non-invasive selection of transgenic embryos before implantation using green fluorescent protein (GFP)

Non-invasive selection of transgenic mice was performed at the stage of preimplantation embryos. The morulae collected from wild female mated with hemizygous transgenic male expressing Aequorea victoria green fluorescent protein (GFP) under chicken beta-actin promoter could be classified as green or non-green under a fluorescent microscope. All the green embryos were shown to carry the transgene by PCR analysis. Taking advantage of the detection of GFP expression can be done non-invasively, the selected embryos were demonstrated to be able to developed to term with 100% of accuracy of the selection.

Expression and analysis of the green fluorescent protein gene in the fission yeast Schizosaccharomyces pombe

This report demonstrates that the Aequorea victoria green fluorescence protein (gfp) gene product will fluoresce in the fission yeast Schizosaccharomyces pombe when expressed from an episomal expression vector. Fluorescence was readily detectable at both the colony and single cell level. Application of fluorescence-activated cell sorting (FACS) techniques showed that gfp-expressing cells could be detected when they were as rare as 1% of a total yeast population. Quantitative analysis of gfp-expressing cells constituting as little as 5% of a total population was possible. These observations establish the suitability of the gfp gene for use in S. pombe and, in combination with FACS, offers an experimental strategy for quantitative analysis of gene expression in yeast populations.

Green-fluorescent protein as a new vital marker in plant cells

The green-fluorescent protein (GFP) from jellyfish Aequorea victoria has been used as a convenient new vital marker in various heterologous systems. However, it has been problematic to express GFP in higher eukaryotes, especially in higher plants. This paper reports that either a strong constitutive or a heat-shock promoter can direct the expression of GFP which is easily detectable in maize mesophyll protoplasts. In this single-cell system, bright green fluorescence emitted from GFP is visible when excited with UV or blue light even in the presence of blue fluorescence from the vacuole or the red chlorophyll autofluorescence from chloroplasts using a fluorescence microscope. No exogenous substrate, co-factor, or other gene product is required. GFP is very stable in plant cells and shows little photobleaching. Viable cells can be obtained after fluorescence-activated cell sorting based on GFP. The paper further reports that GFP can be detected in intact tissues after delivering the constructs into Arabidopsis leaf and root by microprojectile bombardment. The successful detection of GFP in plant cells relies on the use of a universal transcription enhancer from maize or the translation enhancer from tobacco mosaic virus (TMV) to boost the expression. This new reporter could be used to monitor gene expression, signal transduction, co-transfection, transformation, protein trafficking and localization, protein-protein interaction, cell separation and purification, and cell lineage in higher plants.

Use of green fluorescent protein for visualization of cell-specific gene expression and subcellular protein localization during sporulation in Bacillus subtilis

We report the use of the green fluorescent protein (GFP) of Aequorea victoria to visualize cell-specific gene expression and protein subcellular localization during sporulation in Bacillus subtilis. Sporangia bearing the gene (gfp) for the green fluorescent protein fused to genes under the control of the sporulation transcription factor sigma F exhibited a forespore-specific pattern of fluorescence. Forespore-specific fluorescence could be detected with fusions to promoters that are utilized with low (csfB) and high (sspE-2G) efficiency by sigma F-containing RNA polymerase. Conversely, a mother cell-specific pattern of fluorescence was observed in sporangia bearing a transcriptional fusion of gfp to a spore coat protein gene (cotE) under the control of sigma E and an in-frame fusion to a regulatory gene (gerE) under the control of sigma K. An in-frame fusion of gfp to cotE demonstrated that GFP can also be used to visualize protein subcellular localization. In sporangia producing the CotE-GFP fusion protein, fluorescence was found to localize around the developing spore, and this localization was dependent upon SpoIVA, a morphogenetic protein known to determine proper localization of CotE.

Green fluorescent protein

Several bioluminescent coelenterates use a secondary fluorescent protein, the green fluorescent protein (GFP), in an energy transfer reaction to produce green light. The most studied of these proteins have been the GFPs from the jellyfish Aequorea victoria and the sea pansy Renilla reniformis. Although the proteins from these organisms are not identical, they are thought to have the same chromophore, which is derived from the primary amino acid sequence of GFP. The differences are thought to be due to changes in the protein environment of the chromophore. Recent interest in these molecules has arisen from the cloning of the Aequorea gfp cDNA and the demonstration that its expression in the absence of other Aequorea proteins results in a fluorescent product. This demonstration indicated that GFP could be used as a marker of gene expression and protein localization in living and fixed tissues. Bacterial, plant and animal (including mammalian) cells all express GFP. The heterologous expression of the gfp cDNA has also meant that it could be mutated to produce proteins with different fluorescent properties. Variants with more intense fluorescence or alterations in the excitation and emission spectra have been produced.

Green fluorescent protein as a new expression marker in mycobacteria

This study describes the use and the advantages of the green fluorescent protein (GFP) as a reporter molecule for mycobacteria. The gfp gene from Aequorea victoria was placed under the control of the hsp60 promoter in the shuttle vector pGFM-11. The gfp expression in the recombinant Mycobacterium smegmatis and BCG was readily detected on agar plates by the development of an intense green fluorescence upon irradiation with long-wave u.v. light. In mycobacteria containing a pGFM-11 derivative that lacks the hsp60 promoter, no fluorescence was observed. However, this plasmid was successfully used as a promoter-probe vector to identify BCG promoters. The fluorescence emission of GFP in mycobacteria harbouring pGFM-11 and grown in liquid media could be quantified by spectrofluorimetry. This allowed for easy assessment of drug susceptibility. As GFP does not require the addition of substrates or co-factors, the green fluorescent bacilli could be directly observed within infected macrophages using fluorescence and laser confocal microscopy, or in tissue sections of infected mice. Finally, infected cells or free-living recombinant mycobacteria could also be analysed by flow cytometry. The GFP thus appears to be a convenient reporter for mycobacteria, allowing tracing of recombinant mycobacteria, isolation of promoters with interesting properties, in vivo drug testing and the development of new diagnostic tools.

Green fluorescent protein as a marker for gene expression and cell biology of mycobacterial interactions with macrophages

The green fluorescent protein (GFP) of the jellyfish Aequorea victoria offers certain advantages over other bioluminescence systems because no exogenously added substrate or co-factors are necessary, and fluorescence can be elicited by irradiation with blue light without exposing the cells producing GFP to invasive treatments. A mycobacterial shuttle-plasmid vector carrying gfp cDNA was constructed and used to generate transcriptional fusions with promoters of interest and to examine their expression in Mycobacterium smegmatis and Mycobacterium bovis BCG grown in macrophages or on laboratory media. The promoters studied were: (i) ahpC from Mycoosis and Mycobacterium leprae, a gene encoding alkyl hydroperoxide reductase which, along with the divergently transcribed regulator oxyR, are homologues of corresponding stress-response systems in enteric bacteria and play a role in isoniazid sensitivity; (ii) mtrA, an M. tuberculosis response regulator belonging to the superfamily of bacterial two-component signal-transduction systems; (iii) hsp60, a previously characterized heat-shock gene from M. bovis; and (iv) tbprc3, a newly isolated promoter from M. tuberculosis. Expression of these promoters in mycobacteria was analysed using epifluorescence microscopy, laser scanning confocal microscopy, fluorescence spectroscopy, and flow cytometry. These approaches permitted assessment of fluorescence prior to and after macrophage infection, and analyses of promoter expression in individual mycobacteria and its distribution within populations of bacterial cells. Bacteria expressing GFP from a strong promoter could be separated by fluorescence-activated cell sorting from cells harbouring the vector used to construct the fusion. In addition, the stable expression of mtrA-gfp fusion in M. bovis BCG facilitated localization and isolation of phagocytic vesicles containing mycobacteria. The experiments presented here suggest that GFP will be a useful tool for analysis of mycobacterial gene expression and a convenient cell biology marker to study mycobacterial interactions with macrophages.

Expression of Aequorea green fluorescent protein in plant cells

The coding region of the green fluorescent protein (GFP) from Aequorea victoria has been fused to the cauliflower mosaic virus 35S promoter and introduced into maize leaf protoplasts. Transient expression of GFP was observed. In addition, the coding region of GFP was fused to an Arabidopsis heat shock promoter and co-transformed with another construct in which GFP has been replaced with chloramphenicol acetyltransferase (CAT). The heat-induced expression of GFP in maize protoplasts parallels that of CAT. While GFP was expressed in both dark-grown and green maize leaf protoplasts, no green fluorescence was observed in similarly transformed Arabidopsis protoplasts.

Green fluorescent protein as a vital marker and reporter of gene expression in Drosophila

We have used the green fluorescent protein (GFP) from the jellyfish Aequorea victoria as a vital marker/reporter in Drosophila melanogaster. Transgenic flies were generated in which GFP was expressed under the transcriptional control of the yeast upstream activating sequence that is recognized by GAL4. These flies were crossed to several GAL4 enhancer trap lines, and expression of GFP was monitored in a variety of tissues during development using confocal microscopy. Here, we show that GFP could be detected in freshly dissected ovaries, imaginal discs, and the larval nervous system without prior fixation or the addition of substrates or antibodies. We also show that expression of GFP could be monitored in intact living embryos and larvae and in cultured egg chambers, allowing us to visualize dynamic changes in gene expression during real time.

p93dis1, which is required for sister chromatid separation, is a novel microtubule and spindle pole body-associating protein phosphorylated at the Cdc2 target sites

Fission yeast cold-sensitive (cs) dis1 mutants are defective in sister chromatid separation. The dis1+ gene was isolated by chromosome walking. The null mutant showed the same phenotype as that of cs mutants. The dis1+ gene product was identified as a novel 93-kD protein, and its localization was determined by use of anti-dis1 antibodies and green fluorescent protein (GFP) tagged to the carboxyl end of p93dis1. The tagged p93dis1 in living cells localizes along cytoplasmic microtubule arrays in interphase and the elongating anaphase spindle in mitosis, but association with the short metaphase spindle microtubules is strikingly reduced. In the spindle, the tagged p93dis1 is enriched at the spindle pole bodies (SPBs). Time-lapse video images of single cells support the localization shift of p93dis1 to the SPBs in metaphase and spindle microtubules in anaphase. The carboxy-terminal fragment, which is essential for Dis1 function, accumulates around the mitotic SPB. We propose that these localization shifts of p93dis1 in mitosis facilitates sister chromatid separation by affecting SPB and anaphase spindle function.

Green fluorescent protein. The green revolution

Green fluorescent protein allows gene expression and protein localization to be observed in living cells.

The jellyfish green fluorescent protein: a new tool for studying ion channel expression and function

Two methods are described for using the jellyfish green fluorescent protein (GFP) as a reporter gene for ion channel expression. GFP fluorescence can be used to identify the transfected cells, and to estimate the relative levels of ion channel expression, in cotransfection experiments. A GFP-NMDAR1 chimera can be constructed that produces a functional, fluorescent receptor subunit. These methods should facilitate studies of ion channel expression, localization, and processing.

Cloning, expression and sequence analysis of cDNA for the Ca(2+)-binding photoprotein, mitrocomin

The primary structure of mitrocomin consists of 190 amino acid residues, with three Ca(2+)-binding sites and a tyrosine residue at the C-terminus. Mitrocomin shows an amino acid sequence homology of 67.9% and 60.7% when compared with aequorin and clytin, respectively. The amino acid residues Cys152, His58, His169, Trp12, Trp86, Trp108, Trp129 and Trp173 are conserved in all three photoproteins, suggesting that they play a role in light emission.

Overexpression and purification of the recombinant Ca2+-binding protein, apoaequorin

The small, monomeric Ca2+-binding photoprotein, aequorin, emits blue light by an intramolecular reaction when mixed with Ca2+. The photoprotein is made up of coelenterazine and molecular oxygen, bound noncovalently to apoaequorin (apoprotein). The chemical steps leading to light emission, involving the oxidative degradation of coelenterazine, have been studied extensively, but little is known about the active site and how the molecule catalyzes the oxidation of coelenterazine. The three-dimensional structure of the protein has not been determined and therefore answers to these questions have remained unavailable. The present paper describes a procedure for preparing fairly large amounts of apoaequorin and aequorin for X-ray crystallographic studies. It consists of fusing the apoaequorin cDNA to the signal peptide coding sequence of the outer membrane protein A of Escherichia coli, which is under the control of the lipoprotein promoter. When the cDNA was expressed in E. coli, a large excess of the recombinant protein was produced and released into the culture medium. Purification of the protein was accomplished by acid precipitation and DEAE-cellulose chromatography. The procedure yielded 7.4 mg of recombinant apoaequorin with a purity greater than 95% from 200 ml of culture medium. On regeneration with coelenterazine, the recombinant aequorin was fully active with Ca2+.

The role of protein synthesis in the chemotaxis and chemiluminescence of human polymorphonuclear leukocytes

We investigated the role of protein synthesis in human polymorphonuclear leukocyte (PMN) chemotaxis and luminol-dependent chemiluminescence (CL). We used cycloheximide and puromycin to inhibit protein synthesis, and determined the extent of synthesis by measurement of 14C-amino acid incorporation. With 2-hour incubations both puromycin at 9.0 X 10(-6) M and cycloheximide at 1.8 X 10(-6) M inhibited PMN protein synthesis. At concentrations of 2-4 X 10(-5) M both cycloheximide and puromycin inhibited PMN-chemotaxis 40 and 55%, respectively. However, inhibition was observed only when using zymosan-activated serum and not formyl-methionyl-phenylalanine as a chemoattractant. Using 2-hour incubations, PMN-CL was also suppressed by puromycin and cycloheximide, at 20 and 40%, respectively. The data demonstrated that protein synthesis had an important role in chemotaxis that was dependent on the chemoattractant and perhaps the cellular receptor involved in that process. CL did not require de novo protein synthesis but appeared to depend on protein(s) with a relatively rapid turnover.

Bacterial bioluminescence: its control and ecological significance

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