Localization, trafficking, and temperature-dependence of the Aequorea green fluorescent protein in cultured vertebrate cells.

The localization, trafficking, and fluorescence of Aequorea green fluorescent protein (GFP) in cultured vertebrate cells transiently transfected with GFP cDNA were studied. Fluorescence of GFP in UV light was found to be strongest when cells were incubated at 30 degrees C but was barely visible at an incubation temperature of 37 degrees C. COS-1 cells, primary chicken embryonic retina cells, and carp epithelial cells were fluorescently labeled under these conditions. GFP was distributed uniformly throughout the cytoplasm and nucleus independent of cell type examined. When GFP was fused to PML protooncogene product, fluorescence was detected in a unique nuclear organelle pattern indistinguishable from that of PML protein, showing the potential use of GFP as a fluorescent tag. To analyze both function and intracellular trafficking of proteins fused to GFP, a GFP-human glucocorticoid receptor fusion construct was prepared. The GFP-human glucocorticoid receptor efficiently transactivated the mouse mammary tumor virus promoter in response to dexamethasone at 30 degrees C but not at 37 degrees C, indicating that temperature is important, even for function of the GFP fusion protein. The dexamethasone-induced translocation of GFP-human glucocorticoid receptor from cytoplasm to nucleus was complete within 15 min; the translocation could be monitored in a single living cell in real time.     

Dynamics of fluorescence fluctuations in green fluorescent protein observed by fluorescence correlation spectroscopy

We have investigated the pH dependence of the dynamics of conformational fluctuations of green fluorescent protein mutants EGFP (F64L/S65T) and GFP-S65T in small ensembles of molecules in solution by using fluorescence correlation spectroscopy (FCS). FCS utilizes time-resolved measurements of fluctuations in the molecular fluorescence emission for determination of the intrinsic dynamics and thermodynamics of all processes that affect the fluorescence. Fluorescence excitation of a bulk solution of EGFP decreases to zero at low pH (pK_a = 5.8) paralleled by a decrease of the absorption at 488 nm and an increase at 400 nm. Protonation of the hydroxyl group of Tyr-66, which is part of the chromophore, induces these changes. When FCS is used the fluctuations in the protonation state of the chromophore are time resolved. The autocorrelation function of fluorescence emission shows contributions from two chemical relaxation processes as well as diffusional concentration fluctuations. The time constant of the fast, pH-dependent chemical process decreases with pH from 300 μs at pH 7 to 45 μs at pH 5, while the time-average fraction of molecules in a nonfluorescent state increases to 80% in the same range. A second, pH-independent, process with a time constant of 340 μs and an associated fraction of 13% nonfluorescent molecules is observed between pH 8 and 11, possibly representing an internal proton transfer process and associated conformational rearrangements. The FCS data provide direct measures of the dynamics and the equilibrium properties of the protonation processes. Thus FCS is a convenient, intrinsically calibrated method for pH measurements in subfemtoliter volumes with nanomolar concentrations of EGFP.     

GFP基因真核表达质粒的构建及其在人胚肾293细胞中的表达

目的 克隆绿色荧光蛋白（GFP）基因并构建真核表达载体，观察其在人胚肾293（下称293细胞）细胞中的表达和分布，为制备自行设计的以λ噬菌体为载体的人类免疫缺陷病毒（HIV）核酸疫苗的阳性对照奠定基础。方法 以克隆好的pUC18／GFP为模板，根据Genbank中GFP的核苷酸序列设计引物，并在引物的5′端分别引入BamHⅠ及XhoⅠ酶切位点，特异性扩增GFP基因。TA克隆后经双酶切、测序等鉴定重组质粒，再经双酶切、连接构建含GFP编码基因的真核表达载体，酶切鉴定分析后，将该重组质粒通过脂质体介导，转染293细胞。荧光显微镜观察GFP在细胞内的表达和分布。结果重组质粒经Barn HⅠ、XhoⅠ双酶切成5．4kb与0．7kb的片断，表明表达载体pcDNA3．1（＋）中插入了GFP基因片断，测序结果表明编码框正确，并在293细胞中获得了表达，分布均匀。结论 pcDNA3．1（＋）／GFP真核表达载体已成功构建，并可在293细胞中表达。     

脂质体介导转染的绿色荧光蛋白基因在骨髓基质细胞内的表达

目的研究脂质体转染法对骨髓基质细胞进行基因修饰的可行性。方法在体外分离和扩增大鼠骨髓基质细胞,用脂质体转染法介导绿色荧光蛋白基因进入到骨髓基质细胞内,荧光显微镜下检测荧光蛋白的表达,台盼兰排斥试验检测转染细胞的活力。结果绿色荧光蛋白可以在大鼠骨髓基质细胞内表达,转染效率为(28.9±3.6)%;脂质体法转染后的细胞活力为(93.6±4.8)%。结论脂质体转染法可以介导外源基因进入到骨髓基质细胞内表达。     

逆转录病毒介导增强型绿色荧光蛋白基因在大鼠骨髓间充质干细胞中的表达

目的:观察逆转录病毒介导绿色荧光蛋白基因在SD大鼠骨髓间充质干细胞(bone marrow stromal cells,BMSCs)中的表达,为干细胞移植机制的研究提供基础.方法:采用密度梯度离心法分离培养BMSCs,诱导培养液诱导其向成脂肪方向分化,行细胞表面抗原鉴定,及油红O染色评价细胞成脂肪情况.在此基础上,采用逆转录病毒pLEGFP-N1对细胞进行荧光蛋白标记,观察细胞形态学改变荧光表达的时间与强度,计算转染率.结果:细胞扩增迅速,形态良好,纯度较高,经诱导后细胞内可见脂滴.逆转录病毒载体pLEGFP-N1成功标记SD大鼠骨髓间充质干细胞,并对4 wk体外培养进行了良好的标记.结论:逆转录病毒pLEGFP-N1转染效率高,转染成功的BMSCs可以长期稳定表达目的基因,是一种理想的病毒载体.     

Structural basis for dual excitation and photoisomerization of the Aequorea victoria green fluorescent protein

The 2.1-Å resolution crystal structure of wild-type green fluorescent protein and comparison of it with the recently determined structure of the Ser-65 → Thr (S65T) mutant explains the dual wavelength absorption and photoisomerization properties of the wild-type protein. The two absorption maxima are caused by a change in the ionization state of the chromophore. The equilibrium between these states appears to be governed by a hydrogen bond network that permits proton transfer between the chromophore and neighboring side chains. The predominant neutral form of the fluorophore maximally absorbs at 395 nm. It is maintained by the carboxylate of Glu-222 through electrostatic repulsion and hydrogen bonding via a bound water molecule and Ser-205. The ionized form of the fluorophore, absorbing at 475 nm, is present in a minor fraction of the native protein. Glu-222 donates its charge to the fluorophore by proton abstraction through a hydrogen bond network, involving Ser-205 and bound water. Further stabilization of the ionized state of the fluorophore occurs through a rearrangement of the side chains of Thr-203 and His-148. UV irradiation shifts the ratio of the two absorption maxima by pumping a proton relay from the neutral chromophore’s excited state to Glu-222. Loss of the Ser-205–Glu-222 hydrogen bond and isomerization of neutral Glu-222 explains the slow return to the equilibrium dark-adapted state of the chromophore. In the S65T structure, steric hindrance by the extra methyl group stabilizes a hydrogen bonding network, which prevents ionization of Glu-222. Therefore the fluorophore is permanently ionized, causing only a 489-nm excitation peak. This new understanding of proton redistribution in green fluorescent protein should enable engineering of environmentally sensitive fluorescent indicators and UV-triggered fluorescent markers of protein diffusion and trafficking in living cells.     

Real-time light-driven dynamics of the fluorescence emission in single green fluorescent protein molecules

Real-time single-molecule fluorescence detection using confocal and near-field scanning optical microscopy has been applied to elucidate the nature of the "on-off" blinking observed in the Ser-65 --> Thr (S65T) mutant of the green fluorescent protein (GFP). Fluorescence time traces as a function of the excitation intensity, with a time resolution of 100 micros and observation times up to 65 s, reveal the existence of a nonemissive state responsible for the long dark intervals in the GFP. We find that excitation intensity has a dramatic effect on the blinking. Whereas the time during which the fluorescence is on becomes shorter as the intensity is increased, the off-times are independent of excitation intensity. Statistical analysis of the on- and off-times renders a characteristic off-time of 1.6 +/- 0.2 s and allows us to calculate a transition yield of approximately 0.5 x 10(-5) from the emissive to the nonemissive state. The saturation excitation intensity at which on- and off-times are equal is approximately 1.5 kW/cm(2). On the basis of the single-molecule data we calculate an absorption cross section of 6.5 x 10(-17) cm(2) for the S65T mutant. These results have important implications for the use of the GFP to follow dynamic processes in time at the single-molecular level.     

Gene transfer and expression of enhanced green fluorescent protein in variant HT-29c cells

AIM: To study the expression of enhanced green fluorescent protein (EGFP) gene in retrovirally transduced variant HT-29 cells. METHODS: The retroviral vector prkat EGFP/neo was constructed and transfected into the 293T cell using a standard calcium phosphate precipitation method. HT-29c cells (selected from HT-29 cells) were transduced by a retroviral vector encoding the GEFP gene. The fluorescence intensity of colorectal carcinoma HT-29c cells after transduced with the EGFP bearing retrovirus was visualized using fluorescence microscope and fluorescence activated cell sorter (FACS) analysis. Multiple biological behaviors of transduced cells such as the proliferating potential and the expression of various antigens were comparatively analyzed between untransduced and transduced cells in vitro. EGFP expression of the fresh tumor tissue was assessed in vivo. RESULTS: After transduced, HT-29c cells displayed a stable and long-term EGFP expression under the nonselective conditions in vitro. After cells were successively cultured to passage 50 in vitro, EGFP expression was still at a high level. Their biological behaviors, such as expression of tumor antigens, proliferation rate and aggregation capability were not different compared to untransduced parental cells in vitro. In subcutaneous tumors, EGFP was stable and highly expressed. CONCLUSION: An EGFP expressing retroviral vector was used to transduce HT-29c cells. The transduced cells show a stable and long-term EGFP expression in vitro and in vivo. These cells with EGFP are a valuable tool for in vivo research of tumor metastatic spread.     

Assembly and movement of a plant virus carrying a green fluorescent protein overcoat.

Potato virus X (PVX) is a filamentous plant virus infecting many members of the family Solanaceae. A modified form of PVX, PVX.GFP-CP which expressed a chimeric gene encoding a fusion between the 27-kDa Aequorea victoria green fluorescent protein and the amino terminus of the 25-kDa PVX coat protein, assembled into virions and moved both locally and systemically. The PVX.GFP-CP virions were over twice the diameter of wild-type PVX virions. Assembly of PVX.GFP-CP virions required the presence of free coat protein subunits in addition to the fusion protein subunits. PVX.GFP-CP virions accumulated as paracrystalline arrays in infected cells similar to those seen in cells infected with wild-type PVX The formation of virions carrying large superficial fusions illustrates a novel approach for production of high levels of foreign proteins in plants. Aggregates of PVX.GFP-CP particles were fluorescent, emitting green light when excited with ultraviolet light and could be imaged using confocal laser scanning microscopy. The detection of virus particles in infected tissue demonstrates the potential of fusions between the green fluorescent protein and virus coat protein for the non-invasive study of virus multiplication and spread.     

Rapid characterization of green fluorescent protein fusion proteins on the molecular and cellular level by fluorescence correlation microscopy

Fluorescence correlation microscopy (FCM) was applied to characterize fusion proteins of the green fluorescent protein (GFP) on the cellular as well as molecular level within seconds in an integrated instrument. FCM combines the inherent sensitivity and high spatial resolution of fluorescence correlation spectroscopy with fluorescence imaging and micropositioning, thereby providing a spectrum of molecular information in the cellular context. Signatures of characteristic parameters derived from the autocorrelation functions served to distinguish a GFP fusion protein of the epidermal growth factor receptor from GFP fluorescence in the endoplasmic reticulum and cytoplasm. Diffusion constants measured for free transiently expressed GFP reproduced values reported previously with other techniques. The accessible concentration range extends from millions to only a few thousand molecules per cell, with single molecule detectability in the femtoliter detection volume. The detailed molecular characterization offered by FCM is fully compatible with automation in sample identification and detection, offering new possibilities for highly integrated high-throughput screening.     

Molecular characterization of weak D phenotypes by site-directed mutagenesis and expression of mutant Rh-green fluorescence protein fusions in K562 cells

BACKGROUND AND OBJECTIVES: Mutations detected in 161 weak D samples from Caucasians have been classified into 16 types. Because flow cytometry using monoclonal anti-D antibodies (mAbs) has shown that weak D red cells display type-specific antigen density, these mutations in transmembranous regions have been assigned weak D phenotypes. The present study attempts to confirm or refute this assignment. MATERIALS AND METHODS: We amplified DNA from four Japanese weak D samples using the polymerase chain reaction (PCR), and directly sequenced the amplified DNA. Using site-directed mutagenesis, we constructed three vectors expressing mutant RHDs-- G212C, V270G (weak D type 1) and G358A (type 2)--in K562 cells. The expression of RhD antigens was examined by flow cytometry using mAbs. RESULTS: A new mutation resulting in a conversion at amino acid residue 212 (Gly to Cys) was detected in a Japanese weak D sample. K562 cells transduced with mutant RhD cDNA reacted weakly in a type-specific manner with mAbs. CONCLUSIONS: The mutations--G212C (new weak D type), V270G (weak D type 1) and G358A (type 2)-- in transmembranous regions had obvious effects on the D epitopes recognized by mAbs. The results of this study provide direct evidence that these mutations can account for weak D phenotypes.     

慢病毒载体介导绿色荧光蛋白基因转染血管内皮祖细胞的实验研究

目的探讨HIV-1来源的慢病毒载体介导绿色荧光蛋白（GFP）基因转染血管内皮祖细胞（EPCs）的可行性和方法。方法用梯度密度离心法分离人脐带血内皮祖细胞,在EGM-2培养基中培养。用细胞免疫荧光染色和流式细胞仪检测其表达情况。以HIV-1来源的慢病毒为载体、以GFP基因为目的基因转染EPCs,MTT法检测不同病毒滴度（MOI）时细胞增殖情况并观察转染率。结果单个核细胞经EGM-2培养基培养1周后即分化成EPCs。GFP转染后48 h细胞即发出绿色荧光。MOI 1∶10转染组细胞转染率低于MOI 1∶50组（P〈0.05）。MOI 1∶50转染后的细胞与未转染GFP组比较,生长曲线无明显差异（P〉0.05）。MOI 1∶100组转染后细胞的增殖处于停滞状态。结论采用HIV-1来源的慢病毒载体介导GFP基因转染标记EPCs是可行的。以MOI 1∶50进行转染对细胞生长影响小,转染效率高。     

Wavelength mutations and posttranslational autoxidation of green fluorescent protein.

The green fluorescent protein (GFP) of the jellyfish Aequorea victoria is an unusual protein with strong visible absorbance and fluorescence from a p-hydroxybenzylidene-imidazolidinone chromophore, which is generated by cyclization and oxidation of the protein's own Ser-Tyr-Gly sequence at positions 65-67. Cloning of the cDNA and heterologous expression of fluorescent protein in a wide variety of organisms indicate that this unique posttranslational modification must be either spontaneous or dependent only on ubiquitous enzymes and reactants. We report that formation of the final fluorophore requires molecular oxygen and proceeds with a time constant (approximately 4 hr at 22 degrees C and atmospheric pO2) independent of dilution, implying that the oxidation does not require enzymes or cofactors. GFP was mutagenized and screened for variants with altered spectra. The most striking mutant fluoresced blue and contained histidine in place of Tyr-66. The availability of two visibly distinct colors should significantly extend the usefulness of GFP in molecular and cell biology by enabling in vivo visualization of differential gene expression and protein localization and measurement of protein association by fluorescence resonance energy transfer.     

Diversity and evolution of the green fluorescent protein family

The family of proteins homologous to the green fluorescent protein (GFP) from Aequorea victoria exhibits striking diversity of features, including several different types of autocatalytically synthesized chromophores. Here we report 11 new members of the family, among which there are 3 red-emitters possessing unusual features, and discuss the similarity relationships within the family in structural, spectroscopic, and evolutionary terms. Phylogenetic analysis has shown that GFP-like proteins from representatives of subclass Zoantharia fall into at least four distinct clades, each clade containing proteins of more than one emission color. This topology suggests multiple recent events of color conversion. Combining this result with previous mutagenesis and structural data, we propose that (i) different chromophore structures are alternative products synthesized within a similar autocatalytic environment, and (ii) the phylogenetic pattern and color diversity in reef Anthozoa is a result of a balance between selection for GFP-like proteins of particular colors and mutation pressure driving the color conversions.     

Establishment of medaka (Oryzias latipes) transgenic lines with the expression of green fluorescent protein fluorescence exclusively in germ cells: a useful model to monitor germ cells in a live vertebrate

We have generated transgenic medaka (teleost, Oryzias latipes), which allow us to monitor germ cells by green fluorescent protein (GFP) fluorescence in live specimens. Two medaka strains, himedaka (orange-red variety) and inbred QurtE, were used. The transgenic lines were achieved by microinjection of a construct containing the putative promoter region and 3' region of the medaka vasa gene (olvas). The intensity of GFP fluorescence increases dramatically in primordial germ cells (PGCs) located in the ventrolateral region of the posterior intestine around stage 25 (the onset of blood circulation). Whole-mount in situ hybridization and monitoring of ectopically located cells by GFP fluorescence suggested that (i) the increase in zygotic olvas expression occurs after PGC specification and (ii) PGCs can maintain their cell characteristics ectopically after stages 20-25. Around the day of hatching, the QurtE strain clearly exhibits sexual dimorphisms in the number of GFP fluorescent germ cells, a finding consistent with the appearance of leucophores, a sex-specific marker of QurtE. The GFP expression persists throughout the later stages in the mature ovary and testis. Thus, these transgenic medaka represent a live vertebrate model to investigate how germ cells migrate to form sexually dimorphic gonads, as well as a potential assay system for environmental substances that may affect gonad development. The use of a transgenic construct as a selective marker to efficiently isolate germ-line-transmitting founders during embryogenesis is also discussed.     

Distribution of fluorescence following injection of recombinant adeno-associated virus encoding green fluorescent protein into the paraventricular nucleus

We have used recombinant type 2 adeno-associated virus to deliver the gene encoding green fluorescent protein into the central nervous system of adult rats. Gene expression, determined by fluorescent microscopy, was observed not only at the site of injection but also in axons following known neuroanatomical pathways. We have demonstrated a spread of enhanced green fluorescent protein from the paraventricular nucleus of the hypothalamus into the median eminence and neurohypophysis. Cell bodies containing enhanced green fluorescent protein were also visualized in the paraventricular nucleus contralateral to the side of injection. These findings suggest that gene transfer by recombinant adeno-associated virus could be used as a tool to investigate hypothalamic-pituitary interactions and, elsewhere in the central nervous system, to trace axonal pathways.     

增强型绿色荧光蛋白基因在日本血吸虫成虫体内的瞬时表达

目的探讨异源性增强型绿色荧光蛋白(EGFP)基因在日本血吸虫成虫体内表达的可能性。方法运用电穿孔技术将质粒pEGFP-C1导入日本血吸虫成虫体内,提取分离体外培养48小时成虫的基因组DNA、总RNA和全虫蛋白,分别用PCR、RT-PCR和Western blot验证转基因在成虫体内的存在、转录和翻译。同时,使用激光共聚焦扫描显微镜对EGFP在成虫体内进行定位。结果PCR和RT-PCR分别成功的扩增出760bp和276bp的预期大小的片断,Western-blot证实了EGFP基因在成虫体内的表达;激光共聚焦显微镜观察到,EGFP主要定位在成虫的皮层,口吸盘和尾部尤为明显。结论电穿孔技术成功地将异源基因引入日本血吸虫成虫体内并获得表达,为转基因血吸虫和基因功能的研究打下基础。     

真核绿色荧光蛋白表达载体pEGFP-C3-MAGE-12的构建与表达

目的构建黑色素瘤抗原基因-12(MAGE-12)绿色荧光蛋白表达载体pEGFP-C3-MAGE-12,并在真核细胞中表达。方法于2005-10～2005-12对郑州大学第一附属医院应用RT-PCR方法,从人肺癌组织中扩增出MAGE-12cDNA基因片段,经过酶切鉴定后,克隆至质粒载体(pGEM-Teasy),测序证实碱基序列无误后,再克隆至真核绿色荧光蛋白表达载体(pEGFP-C3)上,并转染真核细胞,观察其在真核细胞中表达。结果经酶切及基因序列分析验证,PCR扩增出944bp的MAGE-12基因并成功构建了真核绿色荧光蛋白表达载体pEGFP-C3-MAGE-12,该重组载体能够在真核细胞中广泛表达。结论成功构建真核绿色荧光蛋白表达载体pEGFP-C3-MAGE-12,为建立肿瘤细胞疫苗打下基础。     

Insertion of enhanced green fluorescent protein into the lysozyme gene creates mice with green fluorescent granulocytes and macrophages

Pluripotent hematopoietic stem cells have been studied extensively, but the events that occur during their differentiation remain largely uncharted. To develop a system that allows the differentiation of cultured multipotent progenitors by time-lapse fluorescence microscopy, myelomonocytic cells were labeled with green fluorescent protein (GFP) in vivo. This was achieved by knocking the enhanced GFP (EGFP) gene into the murine lysozyme M (lys) locus and using a targeting vector, which contains a neomycin resistant (neo) gene flanked by LoxP sites and "splinked" ends, to increase the frequency of homologous recombination. Analysis of the blood and bone marrow of the lys-EGFP mice revealed that most myelomonocytic cells, especially mature neutrophil granulocytes, were fluorescence-positive, while cells from other lineages were not. Removal of the neo gene through breeding of the mice with the Cre-deleter strain led to an increased fluorescence intensity. Mice with an inactivation of both copies of the lys gene developed normally and were fertile. (Blood. 2000;96:719-726)     

Visualization of glucocorticoid receptor translocation and intranuclear organization in living cells with a green fluorescent protein chimera.

A highly fluorescent mutant form of the green fluorescent protein (GFP) has been fused to the rat glucocorticoid receptor (GR). When GFP-GR is expressed in living mouse cells, it is competent for normal transactivation of the GR-responsive mouse mammary tumor virus promoter. The unliganded GFP-GR resides in the cytoplasm and translocates to the nucleus in a hormone-dependent manner with ligand specificity similar to that of the native GR receptor. Due to the resistance of the mutant GFP to photobleaching, the translocation process can be studied by time-lapse video microscopy. Confocal laser scanning microscopy showed nuclear accumulation in a discrete series of foci, excluding nucleoli. Complete receptor translocation is induced with RU486 (a ligand with little agonist activity), although concentration into nuclear foci is not observed. This reproducible pattern of transactivation-competent GR reveals a previously undescribed intranuclear architecture of GR target sites.