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The Ly-6A (Sca-1) GFP transgene is expressed in all adult mouse hematopoietic stem cells.

The Sca-1 cell surface glycoprotein is used routinely as a marker of adult hematopoietic stem cells (HSCs), allowing a >100-fold enrichment of these rare cells from the bone marrow of the adult mouse. The Sca-1 protein is encoded by the Ly-6A/E gene, a small 4-exon gene that is tightly controlled in its expression in HSCs and several hematopoietic cell types. For the ability to sort and localize HSCs directly from the mouse, we initiated a transgenic approach in which we created Ly-6A (Sca-1) green fluorescent protein (GFP) transgenic mice. We show here that a 14-kb Ly-6A expression cassette directs the transcription of the GFP marker gene in all functional repopulating HSCs in the adult bone marrow. A >100-fold enrichment of HSCs occurred by sorting for the GFP-expressing cells. Furthermore, as shown by fluorescence-activated cell sorting and histologic analysis of several hematopoietic tissues, the GFP transgene expression pattern generally corresponded to that of Sca-1. Thus, the Ly-6A GFP transgene facilitates the enrichment of HSCs and presents the likelihood of identifying HSCs in situ.

Age Factors↗

Visualization of GFP-expressing tumors and metastasis in vivo.

We have developed mouse models of metastatic cancer with genetically fluorescent tumors that can be imaged in fresh tissue, in situ, as well as externally. To achieve this capability, we have transduced the green fluorescent protein (GFP) gene, cloned from the bioluminescent jellyfish Aequorea victoria, into a series of human and rodent cancer cell lines that were selected in vitro to stably express GFP in vivo after transplantation to metastatic rodent models. Techniques were also developed for transduction of tumors by GFP in vivo. With this fluorescent tool, we detected and visualized for the first time tumors and metastasis in fresh viable tissue or in situ in host organs down to the single-cell level. GFP tumors on the colon, prostate, breast, brain, liver, lymph nodes, lung, pancreas, bone, and other organs can also be visualized externally, transcutaneously by quantitative whole-body fluorescence optical imaging. Real-time tumor and metastatic growth and angiogenesis and inhibition by representative drugs can be imaged and quantified for rapid antitumor, antimetastatic, and antiangiogenesis drug screening. The GFP-transfected tumor cells enabled a fundamental advance in the visualization of tumor growth and metastasis in real time in vivo.

3T3 Cells↗

In vitro assay for site-specific proteases using bead-attached GFP substrate.

Site-specific proteases, which catalyze cleavage of peptide bonds in specific amino acid sequences of target proteins, play important roles in various biological events of many living organisms. In humans, disruption in regulation of these site-specific proteases can lead to pathological consequences. Here, we report a simple in vitro assay for enzymatic activities of site-specific proteases. This assay system employs a protein substrate molecule that is comprised of (i) His-tag binding module, (ii) cleavage sites, and (iii) green fluorescent protein (GFP) detection module. In this study, prostate-specific antigen (PSA) and Thrombin-specific cleavage sites were introduced into the substrate molecules. The overexpressed GFP substrate protein was purified with the aid of Ni++-charged magnetic beads. On cleavage by either PSA or Thrombin, GFP was released from the bound magnetic beads, enabling a direct measurement of the cleaved product by fluorescence. Detection sensitivity, as well as the kinetics of reaction of PSA cleavage with the GFP substrate, was similar or better than commercially available PSA fluorogenic peptide substrate. This bead-attached GFP substrate was also used for an inhibition assay using a competitive inhibitor of Thrombin. In conclusion, this assay offers a simple fluorescent method for monitoring the activity of the site-specific proteases. Furthermore, this system provides flexible means of incorporating varying sizes of flanking sequences adjacent to the cleavage site, which can be essential for studying the regulatory macromolecular interactions between proteases and their substrates.

Animals↗

Two-color GFP expression system for C. elegans.

We describe the use of modified versions of the Aequora victoria green fluorescent protein (GFP) to simultaneously follow the expression and distribution of two different proteins in the nematode, Caenorhabditis elegans. A cyan-colored GFP derivative, designated CFP, contains amino acid (aa) substitutions Y66W, N146I, M153T and V163A relative to the original GFP sequence and is similar to the previously reported "W7" form. A yellow-shifted GFP derivative, designated YFP, contains aa substitutions S65G, V68A, S72A and T203Y and is similar to the previously described "I0C" variant. Coding regions for CFP and YFP were constructed in the context of a high-activity C. elegans expression system. Previously characterized promoters and localization signals have been used to express CFP and YFP in C. elegans. Filter sets designed to distinguish YFP and CFP fluorescence spectra allowed visualization of the two distinct forms of GFP in neurons and in muscle cells. A series of expression vectors carrying CFP and YFP have been constructed and are being made available to the scientific community.

Amino Acid Substitution↗

Model system for plant cell biology: GFP imaging in living onion epidermal cells.

The ability to visualize organelle localization and dynamics is very useful in studying cellular physiological events. Until recently, this has been accomplished using a variety of staining methods. However, staining can give inaccurate information due to nonspecific staining, diffusion of the stain or through toxic effects. The ability to target green fluorescent protein (GFP) to various organelles allows for specific labeling of organelles in vivo. The disadvantages of GFP thus far have been the time and money involved in developing stable transformants or maintaining cell cultures for transient expression. In this paper, we present a rapid transient expression system using onion epidermal peels. We have localized GFP to various cellular compartments (including the cell wall) to illustrate the utility of this method and to visualize dynamics of these compartments. The onion epidermis has large, living, transparent cells in a monolayer, making them ideal for visualizing GFP. This method is easy and inexpensive, and it allows for testing of new GFP fusion proteins in a living tissue to determine deleterious effects and the ability to express before stable transformants are attempted.

Cloning, Molecular↗

Epithelial localization of green fluorescent protein-positive cells in epididymis of the GAD67-GFP knock-in mouse.

gamma-Aminobutyric acid (GABA), which is a major inhibitory neurotransmitter in the brain, is also found in many peripheral nonneuronal tissues, including male reproductive organs. However, the distribution of GABAergic cells in various organs is not known. The GAD67-GFP knock-in mouse is a useful model for studying the distribution and morphology of GABAergic neurons in the brain. We examined the male reproductive organs of GAD67-GFP knock-in mice by fluorescence microscopy and found cells with strong green fluorescent protein (GFP) signal exclusively in the epithelium of the initial segment and proximal caput of the epididymis. The characteristic cell morphology suggested that these were narrow cells. These GFP-positive narrow cells also expressed GAD67 and GABA. Reverse transcription polymerase chain reaction (RT-PCR) analysis showed that the predominant glutamic acid decarboxylase (GAD) isoform expressed in the epididymis is GAD67. RT-PCR analysis also revealed that mRNAs encoding the GABA(A) and GABA(B) receptor subunits necessary for the assembly of functional receptors are expressed in the epididymis. GABA(A) receptor subunit mRNAs detected in the proximal epididymis included alpha2, beta1, gamma1, and gamma3, and both the R1 and R2 subunit mRNAs of GABA(B) receptors were detected. Immunohistochemical analysis of GABA(A) receptor subunit proteins revealed that alpha2, beta1, and gamma subunits expressed in spermatozoa, whereas we did not detect these GABA(A) receptor subunits in epithelial cells. GABA(B) receptors were produced by narrow cells and spermatozoa of GAD67-GFP knock-in and wild-type Jcl:ICR mice. Our data suggest that the GABA system might have important functional roles in narrow cells and on spermatozoa in the lumen.

Animals↗

Monitoring GFP-operon fusion protein expression during high cell density cultivation of Escherichia coli using an on-line optical sensor.

Synthesis of an operon fusion protein was investigated in batch and fed-batch cultures at high cell densities of recombinant Escherichia coli JM105 [pBAD-GFP::CAT]. Glucose-limited growth was achieved without accumulation of inhibitory byproducts allowing high cell densities (110 g L(-1) DCW) to be attained. This was believed to be the highest reported value for dry cell mass of E. coli strain JM105 expressing two recombinant proteins. Transcription of the two reporter genes, green fluorescent protein (GFP) and chloramphenicol acetyltransferase (CAT), was under the control of the p(BAD) promoter of the araBAD (arabinose) operon. Each protein was independently translated via separate ribosome binding sites. CAT served as a model recombinant protein product to illustrate the noninvasive quantitative reporting ability of GFP during high cell density fermentations. Expression of GFP was monitored on-line using an intensity-based optical sensor. A linear correlation between the on-line GFP intensity and the enzymatic activity of CAT allowed for in vivo real-time quantitative monitoring of a fermentation product under conditions of high biomass concentration and high productivity.

Arabinose↗

Inactivation of a GFP retrovirus occurs at multiple levels in long-term repopulating stem cells and their differentiated progeny.

Hematopoietic stem cell gene therapy holds promise for the treatment of many hematologic disorders. One major variable that has limited the overall success of gene therapy to date is the lack of sustained gene expression from viral vectors in transduced stem cell populations. To understand the basis for reduced gene expression at a single-cell level, we have used a murine retroviral vector, MFG, that expresses the green fluorescent protein (GFP) to transduce purified populations of long-term self-renewing hematopoietic stem cells (LT-HSC) isolated using the fluorescence-activated cell sorter. Limiting dilution reconstitution of lethally irradiated recipient mice with 100% transduced, GFP(+) LT-HSC showed that silencing of gene expression occurred rapidly in most integration events at the LT-HSC level, irrespective of the initial levels of GFP expression. When inactivation occurred at the LT-HSC level, there was no GFP expression in any hematopoietic lineage clonally derived from silenced LT-HSC. Inactivation downstream of LT-HSC that stably expressed GFP( )in long-term reconstituted animals was restricted primarily to lymphoid cells. These observations suggest at least 2 distinct mechanisms of silencing retrovirally expressed genes in hematopoietic cells.

Animals↗

Use of Staphylococcus aureus 6-P-beta-galactosidase and GFP as fusion partners for lactose-specific IIC domain from Staphylococcus aureus.

The hydrophilic part of membrane proteins plays an important role in the formation of 3D crystals. The construction of fusion proteins using well crystallizing proteins as fusion partners is a possibility to increase the hydrophilic part of membrane proteins lacking large hydrophilic domains. These fusion proteins might be easier to crystallize. Two bifunctional fusion proteins containing the membrane-bound, lactose-specific enzyme IIC domain of the lactose transporter (IICB(lac)) from S. aureus as N-terminal fusion partner were constructed by gene fusion. The C-terminal fusion partners were S. aureus 6-P-beta-Galactosidase and GFP, respectively. Both proteins were overexpressed in E. coli, purified to homogeneity and kinetically characterized: In the presence of the components of the lactose phosphotransferase system of S. aureus, the hybrid proteins phosphorylated their substrates, indicating that the fusion partners are sufficiently flexibly linked to allow the interaction of the IIC(lac) domain with the IIB(lac) domain of the lactose transporter. The activity of the 6-P-beta-Galactosidase as well as the fluorescence of GFP were preserved in the fusion proteins. The Vmax values determined for the IIC domain in the fusion proteins were dramatically reduced compared with the values determined for the separate IIC(lac) domain and the complete lactose transporter (IICB(lac)). The Km values were only slightly increased indicating that the Vmax values are much more influenced by the fusion than the substrate affinities. The substrate affinity and the Vmax value determined for the GFP-fused IIC(lac) domain are higher than for the 6-P-beta-Galactosidase-fused IIC(lac). The results suggest that the fusion with GFP enables a better interaction with the IIB(lac) domain than the fusion with 6-P-beta-Galactosidase. Moreover, the GFP-fused IIC(lac) domain proved to be more stable than the 6-P-beta-Galactosidase fusion protein.

Amino Acid Sequence↗

[Long-term outcome of gfp gene modified human RPE xenografts into the subretinal space of rabbits].

The possibility of delivery genes to retina by using retinal pigment epithelium (RPE) transplantation was investigated. Cultured human adult RPE cells were transfected with retrovirus encoding green fluorescent protein (GFP), then GFP-expressing RPE cells were transplanted into the subretinal space of rabbits through pars plana vitrectomy under microscopy. The transplant sites were examined in vivo by ophthalmoscope for fluorescence. The animals were euthanatized at 1, 2, 3, 4, 6, 10, 11, 14, 18, 20, 23, 24, 25, 33, 54 weeks, respectively, and the retinas were studied histologically, including epi-fluorescent microscopy, confocal microscopy and transmission electron microscopy. The GFP-expressing transplant could be followed in the living retina up to 21 days by ophthalmoscope. The epi-fluorescent microscopy examination disclosed survival of the transplanted cells in 1 year with continual and significant GFP expression. It was observed the transplanted hRPE-gfp cells were not only present at transplant sites but spread over two to three quarters of retina. Generally, RPE xenografts integrated individually into host RPE in a regular cobblestones arrangement or formed a monolayer sheet between host RPE and neural retina. It was observed that intravitreal injection of FK-506 weekly improved the survival of RPE xenografts and reduced the infiltration of mononuclear microphages and lymphocytes in choroids from 1 through 14 weeks after transplantation. The results demonstrate a long-term survival of gene modified human RPE xenografts into the subretinal space of rabbits and support the feasibility of this approach for delivery genes to retina.

Adult↗

[Study of osteoblasts transfected with gfp in vitro and traced in vivo].

OBJECTIVE: To observe the osteoblasts transfected with green fluorescent protein (GFP)by adenovirus vector expressed in vitro and traced it in vivo in order to research the feasibility of GFP as a tracer of seeding cells for tissue engineering. METHODS: CFP were transfected into the osteoblasts which derived from adult human bone marrow stromal cell (hBMSc) by adenovirus vector after being packed in 293A cells. The nontransfected hBMSc was used as the control group. The osteoblasts in each group were observed under an inverted phase contrast microscope and fluorescence microscope. The expressive efficiency of GFP was examined by flow cytometry,and alkaline phosphatase (ALP) activities and osteocalcin (OCN) synthesis. After eight days of the transfection,the osteoblasts were implanted into the muscle of nude mouse thigh while the non-transfected osteoblasts were also implanted as a control. Four and eight weeks after the operation, the nude rats were killed and the continuous tissue sections were examined using fluorescence microscopy after adjacent sections were performed by immunohistochemistry or routine HE staining. RESULTS: The green fluorescence was shown the transfected osteoblasts which derived from bone marrow. The rate of positive expression was over 75%. After eight days of the transfection, the marker proteins of the surface of the osteoblasts showed extremely efficient expression of CD29 and CD44, but the CD34 expressed negative. Either ALP or OCN of the osteoblasts was no significant difference between the two groups (P > 0.05) four and eight days after the transfection. The GFP were obviously expressed in nude mouse both at four and eight weeks, meanwhile it did not harm on the morphology and function of the transfected osteoblasts whose immunohistochemistry examination showed positive reaction. CONCLUSIONS: GFP could be transfected osteoblasts effectively in vitro and traced in vivo in nude mouse. It may be an optimal tracer for living cells on tissue engineering research.

Adult↗

Internalization of a GFP-tetanus toxin C-terminal fragment fusion protein at mature mouse neuromuscular junctions.

The distribution, dynamics, internalization, and retrograde axonal traffic of a fusion protein composed of green fluorescent protein (GFP)and the atoxic C-terminal fragment of tetanus toxin (TTC) were studied after its in vivo injection. Confocal microscopy and immuno-gold electron microscopy revealed that the fusion protein (GFP-TTC) rapidly clustered in motor nerve terminals of the neuromuscular junction. Clathrin-coated pits, and axolemma infoldings located between active zones appeared to be involved in the internalization of the fusion protein. Biochemical analysis of detergent-extracted neuromuscular preparations showed that the GFP-TTC fusion protein was associated with lipid microdomains. We suggest that GFP-TTC clustering in these lipid microdomains favors the recruitment of other proteins involved in its endocytosis and internalization in motor nerve terminals. During its retrograde trafficking, GFP-TTC accumulated indifferent axonal compartments than those used by cholera toxin B-subunit suggesting that these two proteins are transported by different pathways and cargos.

Animals↗

Monitoring the disruption of nuclear envelopes in interphase cells with GFP-beta-galactosidase.

The nuclear envelope of eukaryotic cells provides a barrier separating nucleus from cytoplasm, thereby regulating the exchange of macromolecules between both compartments. However, in cells exposed to severe forms of stress this barrier may break down, resulting in the mixing of nuclear and cytoplasmic contents. We show here that the fusion protein GFP-beta-galactosidase can be used to evaluate the intactness of nuclear envelopes in HeLa cells that have been exposed to heat and oxidative stress. GFP-beta-galactosidase is restricted to the cytoplasm of interphase cells, but enters the nucleus when nuclear membranes are disrupted. For comparison, we have analyzed the barrier function of nuclear membranes with antibodies against lamin B. Treatment of fixed cells with digitonin permeabilizes the plasma membrane, but leaves nuclear envelopes intact. Consequently, after digitonin incubation antibodies to lamin B can bind their antigen only if nuclear membranes are damaged. For various heat and oxidative stress conditions, we have compared the distribution of GFP-beta-galactosidase with the accessibility of lamin B to antibodies. Our results demonstrate that nuclear envelopes are permeable to antibodies whenever GFP-beta-galactosidase enters the nucleus. GFP-beta-galactosidase is therefore a useful tool for evaluating the disintegration of the nuclear envelope and identifying cells in which a mixing of nuclear and cytoplasmic material takes place.

Fluorescent Antibody Technique, Indirect↗

Heterologous HIS3 marker and GFP reporter modules for PCR-targeting in Saccharomyces cerevisiae.

We have fused the open reading frames of his3-complementing genes from Saccharomyces kluyveri and Schizosac-charomyces pombe to the strong TEF gene promotor of the filamentous fungus Ashbya gossypii. Both chimeric modules and the cognate S. kluyveri HIS3 gene were tested in transformations of his3 S. cerevisiae strains using PCR fragments flanked by 40 bp target guide sequences. The 1.4 kb chimeric Sz. pombe module (HIS3MX6) performed best. With less than 5% incorrectly targeted transformants, it functions as reliably as the widely used geniticin resistance marker kanMX. The rare false-positive His+ transformants seem to be due to non-homologous recombination rather than to gene conversion of the mutated endogenous his3 allele. We also cloned the green fluorescent protein gene from Aequorea victoria into our pFA-plasmids with HIS3MX6 and kanMX markers. The 0.9 kb GFP reporters consist of wild-type GFP or GFP-S65T coding sequences, lacking the ATG, fused to the S. cerevisiae ADH1 terminator. PCR-synthesized 2.4 kb-long double modules flanked by 40-45 bp-long guide sequences were successfully targeted to the carboxy-terminus of a number of S. cerevisiae genes. We could estimate that only about 10% of the transformants carried inactivating mutations in the GFP reporter.

Acyltransferases↗

Faithful expression of green fluorescent protein (GFP) in transgenic zebrafish embryos under control of zebrafish gene promoters.

Although the zebrafish has become a popular model organism for vertebrate developmental and genetic analyses, its use in transgenic studies still suffers from the scarcity of homologous gene promoters. In the present study, three different zebrafish cDNA clones were isolated and sequenced completely, and their expression patterns were characterized by whole-mount in situ hybridization as well as by Northern blot hybridization. The first clone encodes a type II cytokeratin (CK), which is specifically expressed in skin epithelia in early embryos and prominently expressed in the adult skin tissue. The second clone is muscle specific and encodes a muscle creatine kinase (MCK). The third clone, expressed ubiquitously in all tissues, is derived from an acidic ribosomal phosphoprotein P0 (arp) gene. In order to test the fidelity of zebrafish embryos in transgenic expression, the promoters of the three genes were isolated using a rapid linker-mediated PCR approach and subsequently ligated to a modified green fluorescent protein (gfp) reporter gene. When the three hybrid GFP constructs were introduced into zebrafish embryos by microinjection, the three promoters were activated faithfully in developing zebrafish embryos. The 2.2-kb ck promoter was sufficient to direct GFP expression in skin epithelia, although a weak expression in muscle was also observed in a few embryos. This pattern of transgenic expression is consistent with the expression pattern of the endogenous cytokeratin gene. The 1.5-kb mck promoter/gfp was expressed exclusively in skeletal muscles and not elsewhere. By contrast, the 0.8-kb ubiquitous promoter plus the first intron of the arp gene were capable of expressing GFP in a variety of tissues, including the skin, muscle, lens, neurons, notochord, and circulating blood cells. Our experiments, therefore, further demonstrated that zebrafish embryos can faithfully express exogenously introduced genes under the control of zebrafish promoters.

Animals↗

Intercellular spread of GFP-VP22.

BACKGROUND: The herpes simplex virus type 1 (HSV-1) VP22 polypeptide has been reported to mediate intercellular trafficking of heterologous proteins fused to its C- or N-terminus, a feature making it a useful tool in bystander cell-targeted gene therapy. METHODS: Here we show, by detection of Green Fluorescent Protein (GFP) fused to VP22, its subcellular distribution in living producer (transfected) and recipient (non-transfected) cells as well as in cells after fixation. Four cell lines from different species were used. RESULTS: Different fractions of translocated GFP-VP22 fusion protein could be detected in fixed recipient cells by two different methods of fixation. Functional GFP in live recipient cells could not be detected. CONCLUSIONS: Our study indicates that the VP22-chimeric protein transfer in its present form is suboptimal in terms of protein function. However, after fixation, the GFP signal in 100% of cells in a monolayer can be detected even at moderate transfection efficiency.

Animals↗

Mouse cytomegalovirus in developing brain tissue: analysis of 11 species with GFP-expressing recombinant virus.

Cytomegaloviruses (CMVs) are species-specific large double-stranded DNA viruses. Mouse and human CMVs have a similar morphology, similar gene sequence, and exert similar cellular effects, but the replication of the virus outside its primary host species is limited. This may confer upon CMV certain advantages for expression of foreign genes or cellular labels in brain cells of nonhost species. We examined the ability of recombinant mouse (m)CMV expressing green fluorescent protein (GFP) to serve as a vector for transgene expression in developing neurons and glia outside the normal host species. For comparative purposes, 11 species were examined. Mouse CMV reporter gene expression was particularly strong in the developing brain of its normal host species, mouse, where it replicated in cultures and brain slices, leading to cell death. All mammalian species tested (human, rat, gerbil, hamster, mouse) showed reporter gene expression after mCMV infection. High levels of mCMV infection were also found in chicken central nervous system cells in vitro, and a low level of mCMV expression was found after an initial delay in turtle neurons and glia. No mCMV reporter gene expression was found in frog cells or aplysia neurons or glia or in drosophila or fungal cells. Infection of nonmouse neurons by low concentrations of mCMV led to strong expression of GFP in dendrites and axons with normal morphology. Despite the lack of replication, high doses of mCMV induced morphologic changes in neurons and glia from hamster and rat brain slices, leading to cells rounding up, and to the formation of giant cells consisting of an aggregate of many cells fused together into a syncytium. In contrast, in human hippocampal slices, GFP-expressing cells infected with mCMV had a relatively normal appearance 12 days after inoculation. To determine whether a CMV from another species could serve as a vector for gene transfer, a recombinant human CMV-expressing GFP was used for transgene expression in rat brain cells in vitro. Cytomegaloviruses thus have potential as useful vectors for gene transfer and labeling central nervous system cells, with the actions of CMV being dependent on a number of factors.

Animals↗

Transgene driving GFP expression from the promoter of the zona pellucida gene zpc is expressed in oocytes and provides an early marker for gonad differentiation in zebrafish.

Although mechanisms of sex differentiation have been studied intensely in mammals, insects, and worms, little is known about this process in lower vertebrates. To establish a marker for female gonad differentiation in zebrafish, we generated a transgenic line in which 412 bp from the promoter and 5' mRNA leader of the female-specific zebrafish zona pellucida gene zpc are fused to the coding region of green fluorescent protein (GFP). The zpc0.5:GFP transgene is expressed exclusively in oocytes, starting from the onset of female-specific differentiation, and closely resembles the expression pattern of the wild-type zpc. Strong GFP expression persists throughout oogenesis and is visible through the body wall of females. We have also characterized a putative upstream factor of zpc, FIGalpha, and show that distribution of FIGalpha RNA is compatible with its postulated role in the regulation of zpc. The zpc0.5:GFP transgenic line described here will be useful for studying oocyte development and the mechanisms that determine sex-specific gene expression in the zebrafish. It is also the first promoter characterized to date to drive stable and efficient expression specifically in the zebrafish female germline.

Amino Acid Sequence↗