Export of Precursor tRNAIle from the Nucleus to the Cytoplasm in Human Cells

In the current concept, tRNA maturation in vertebrate cells, including splicing of introns, trimming of 5’ leader and 3’ trailer, and adding of CCA, is thought to occur exclusively in the nucleus. Here we provide evidence to challenge this concept. Unspliced intron-containing precursor tRNA^Ile was identified in Human Immunodeficiency Virus type 1 (HIV-1) virions, which are synthesized in the cytoplasm. Northern blot, confocal microscopy and quantitative RT-PCR further verified enrichment of this unspliced tRNA^Ile within the cytoplasm in human cells. In addition to containing an intron, the cytoplasmic precursor tRNA^Ile also contains a short incompletely processed 5´ leader and a 3´ trailer, which abundance is around 1000 fold higher than the nuclear precursor tRNA^Ile with long 5’ leader and long 3’ trailer. In vitro data also suggest that the cytoplasmic unspliced end-immature precursor tRNA^Ile could be processed by short isoform of RNase Z, but not long isoform of RNase Z. These data suggest that precursor tRNAs could export from the nucleus to the cytoplasm in human cells, instead of be processed only in the nucleus.     

膜锚定Gaussia萤光素酶的细胞标记及生物荧光成像

目的:制备表达膜锚定Gaussia萤光素酶(extGluc)报告基因的慢病毒,用于标记细胞。方法:将报告基因extGluc克隆至慢病毒载体pCCsin.PPT.SFFV.IRES.eGFP.Wpre(VeGFP)中,以聚乙烯亚胺(PEI)介导,将慢病毒包装所需4种质粒(pVeGFP-extGLuc、pMDL、pRev、pVSVG),转染293FT细胞,72 h后收集病毒上清进行浓缩,感染293FT细胞,并用流式细胞仪检测病毒滴度,生物荧光成像和化学发光分析extGluc的表达;之后,用收集的慢病毒感染人单核细胞白血病细胞株U937。结果:对经PCR筛选出的阳性克隆所含质粒进行酶切鉴定,表明extGlu报告基因插入载体中;重组慢病毒包装成功且病毒滴度为5×106 TU/mL;用包装的病毒颗粒感染293FT细胞,生物荧光成像和化学发光证实extGluc的膜定位,且酶活性与细胞数目呈线性相关;病毒颗粒能够感染悬浮细胞U937。结论:包装了extGluc标记的重组慢病毒,可用于标记细胞,为体内监测细胞迁移、聚集和变化提供了一种方法。     

有机荧光团及荧光标记细胞的阴极荧光成像研究

目的 阴极荧光（CL）成像是一种以电子束为激发源的高分辨荧光成像技术,但生物材料对电子束的敏感性限制了CL技术在生命科学中的广泛应用。为了研究和发展CL技术在生物样品中的应用,本文旨在通过探究电子辐照引起碳基材料的结构损伤、有机基团的降解及荧光猝灭等问题,深入理解电子源对有机荧光团的激发特性。方法 本研究应用扫描电镜（SEM）和阴极荧光谱仪系统（SEM-CL）,研究电子源对有机荧光团及荧光探针标记细胞的激发特性,观测了有机物的CL信号的发射特性、强度衰减、成像方式及特点。结果 实验结果显示,在低能量（2.5～5 keV）和低束流（～10 pA）电子辐照下,有机荧光微珠发射出较强的荧光,CL像分辨率达到～30 nm。荧光微珠经过12 min辐照,信号强度衰减了25%,CL像仍保持了可接受的发光强度和足够的信噪比。此外,还获得了从细胞表面到内部一定深度内,荧光标记的亚细胞结构信息。结论 在SEM-CL系统中,可以同时获得由电子束激发产生的电子像和CL像,实现阴极荧光与电子显微镜关联（CCLEM）成像。本实验的研究结果为CCLEM技术应用于生物结构研究提供了数据及技术支持。     

Nucleic Acid Synthesis in Cytoplasm of Yaba Monkey Tumor Virus-Infected Cells

Yaba tumor virus progeny appeared in cynomolgus monkey kidney cells at 24 h postinfection and reached a plateau at 72 h in the first cycle of replication. Viral DNA synthesis was first detected at about 3 h and reached a peak in 18 h. Maximum coating of viral DNA in infected cells occurred at 4 days postinfection. Rapidly labeled RNA was synthesized in the cytoplasm of virus-infected cells. At 6 h postinfection 7 to 10S RNA was present; this species was present in greater amount at 12 h; at 24 h a truncated peak indicated the presence of 14 to 15S as well as 7 to 10S RNA. Hybridization data indicated that the largest peak of messenger RNA synthesis occurred at 11 to 13 h postinfection and a second, slightly smaller, peak occurred at 21 to 23 h.     

Virus-Specific Ribonucleic Acid in the Nucleus and Cytoplasm of Rat Embryo Cells Transformed by Adenovirus Type 2

Nuclei were isolated from rat embryo cells transformed by adenovirus type 2. Nuclear and cytoplasmic virus-specific ribonucleic acids (RNA) were characterized and quantitated by deoxyribonucleic acid (DNA)-RNA hybrid formation with adenovirus DNA. The results indicate that most, if not all, virus-specific RNA molecules are synthesized in the cell nucleus and subsequently transported into cytoplasm where they degrade with a half-life of 1 to 2 hr. No difference in base sequences between nuclear and cytoplasmic virus-specific RNA species can be detected by hybridization competition experiment with viral DNA.     

Translational Diffusion of Macromolecule-sized Solutes in Cytoplasm and Nucleus

Fluorescence recovery after photobleaching (FRAP) was used to quantify the translational diffusion of microinjected FITC-dextrans and Ficolls in the cytoplasm and nucleus of MDCK epithelial cells and Swiss 3T3 fibroblasts. Absolute diffusion coefficients (D) were measured using a microsecond-resolution FRAP apparatus and solution standards. In aqueous media (viscosity 1 cP), D for the FITC-dextrans decreased from 75 to 8.4 × 10⁻⁷ cm²/s with increasing dextran size (4–2,000 kD). D in cytoplasm relative to that in water (D/D_o) was 0.26 ± 0.01 (MDCK) and 0.27 ± 0.01 (fibroblasts), and independent of FITC-dextran and Ficoll size (gyration radii [R_G] 40–300 Å). The fraction of mobile FITC-dextran molecules (f_mob), determined by the extent of fluorescence recovery after spot photobleaching, was >0.75 for R_G < 200 Å, but decreased to <0.5 for R_G > 300 Å. The independence of D/D_o on FITC-dextran and Ficoll size does not support the concept of solute “sieving” (size-dependent diffusion) in cytoplasm. Photobleaching measurements using different spot diameters (1.5–4 μm) gave similar D/D_o, indicating that microcompartments, if present, are of submicron size. Measurements of D/D_o and f_mob in concentrated dextran solutions, as well as in swollen and shrunken cells, suggested that the low f_mob for very large macromolecules might be related to restrictions imposed by immobile obstacles (such as microcompartments) or to anomalous diffusion (such as percolation). In nucleus, D/D_o was 0.25 ± 0.02 (MDCK) and 0.27 ± 0.03 (fibroblasts), and independent of solute size (R_G 40–300 Å). Our results indicate relatively free and rapid diffusion of macromolecule-sized solutes up to approximately 500 kD in cytoplasm and nucleus.     

Two-photon Imaging of Cellular Dynamics in the Mouse Spinal Cord

Two-photon (2P) microscopy is utilized to reveal cellular dynamics and interactions deep within living, intact tissues. Here, we present a method for live-cell imaging in the murine spinal cord. This technique is uniquely suited to analyze neural precursor cell (NPC) dynamics following transplantation into spinal cords undergoing neuroinflammatory demyelinating disorders. NPCs migrate to sites of axonal damage, proliferate, differentiate into oligodendrocytes, and participate in direct remyelination. NPCs are thereby a promising therapeutic treatment to ameliorate chronic demyelinating diseases. Because transplanted NPCs migrate to the damaged areas on the ventral side of the spinal cord, traditional intravital 2P imaging is impossible, and only information on static interactions was previously available using histochemical staining approaches. Although this method was generated to image transplanted NPCs in the ventral spinal cord, it can be applied to numerous studies of transplanted and endogenous cells throughout the entire spinal cord. In this article, we demonstrate the preparation and imaging of a spinal cord with enhanced yellow fluorescent protein-expressing axons and enhanced green fluorescent protein-expressing transplanted NPCs.     

基于活体成像的表达人PSCA抗原的小鼠肿瘤模型的建立

目的:探讨并建立可供药物评价或生物学功能研究的表达人PSCA抗原的荧光素酶小鼠肿瘤模型。方法:克隆人PSCA基因及荧光素酶基因luc,构建真核表达质粒pcDNA-PSCA及pcDNA-luc,共转染RM-1细胞株;照度计检测转染细胞的荧光素酶活性,RT-PCR及流式细胞术检测PSCA的表达,筛选出共表达荧光素酶及人PSCA的RM-PSCA/luc细胞株;将RM-PSCA/luc细胞接种C57BL/6小鼠,观察所致肿瘤的生长情况及小鼠存活状况,并对小鼠进行活体成像检测Luc的表达;采用免疫组织化学染色方法检测人PSCA在小鼠肿瘤组织中的表达。结果:筛选到了稳定共表达Luc及人PSCA抗原的RM-PSCA/luc细胞,接种实验小鼠全部成瘤,肿瘤生长迅速,小鼠平均存活38天;转染荧光素酶基因的肿瘤细胞生物特性稳定,活体成像仪检测到转染荧光素酶细胞在小鼠体内活体成像,荧光素酶表达活性的强弱能够反映肿瘤大小;免疫组织化学染色方法检测到小鼠肿瘤组织PSCA的表达。结论:成功构建了可用于活体成像表达人PSCA抗原的小鼠肿瘤模型,为相关肿瘤药物及疫苗的研发奠定基础。     

Coilin Shuttles between the Nucleus and Cytoplasm In Xenopus Oocytes

Coiled bodies are discrete nuclear organelles often identified by the marker protein p80-coilin. Because coilin is not detected in the cytoplasm by immunofluorescence and Western blotting, it has been considered an exclusively nuclear protein. In the Xenopus germinal vesicle (GV), most coilin actually resides in the nucleoplasm, although it is highly concentrated in 50-100 coiled bodies. When affinity-purified anti-coilin antibodies were injected into the cytoplasm of oocytes, they could be detected in coiled bodies within 2-3 h. Coiled bodies were intensely labeled after 18 h, whereas other nuclear organelles remained negative. Because the nuclear envelope does not allow passive diffusion of immunoglobulins, this observation suggests that anti-coilin antibodies are imported into the nucleus as an antigen-antibody complex with coilin. Newly synthesized coilin is not required, because cycloheximide had no effect on nuclear import and subsequent targeting of the antibodies. Additional experiments with myc-tagged coilin and myc-tagged pyruvate kinase confirmed that coilin is a shuttling protein. The shuttling of Nopp140, NO38/B23, and nucleolin was easily demonstrated by the targeting of their respective antibodies to the nucleoli, whereas anti-SC35 did not enter the germinal vesicle. We suggest that coilin, perhaps in association with Nopp140, may function as part of a transport system between the cytoplasm and the coiled bodies.     

Investigation of the Internalization of Fluorescently Labeled Lipophilic siRNA into Cultured Tumor Cells

Russian Journal of Bioorganic Chemistry - The attachment of lipophilic molecules of natural origin, which have natural means for cell internalization, to small interfering RNA (siRNA) is an...     

Imaging Cellular Inorganic Phosphate in Caenorhabditis elegans Using a Genetically Encoded FRET-Based Biosensor

Inorganic phosphate (Pi) has central roles in metabolism, cell signaling and energy conversion. The distribution of Pi to each cell and cellular compartment of an animal must be tightly coordinated with its dietary supply and with the varied metabolic demands of individual cells. An analytical method for monitoring Pi dynamics with spatial and temporal resolution is therefore needed to gain a comprehensive understanding of mechanisms governing the transport and recycling of this essential nutrient. Here we demonstrate the utility of a genetically encoded FRET-based Pi sensor to assess cellular Pi levels in the nematode Caenorhabditis elegans. The sensor was expressed in different cells and tissues of the animal, including head neurons, tail neurons, pharyngeal muscle, and the intestine. Cytosolic Pi concentrations were monitored using ratiometric imaging. Injection of phosphate buffer into intestinal cells confirmed that the sensor was responsive to changes in Pi concentration in vivo. Live Pi imaging revealed cell-specific and developmental stage-specific differences in cytosolic Pi concentrations. In addition, cellular Pi levels were perturbed by food deprivation and by exposure to the respiratory inhibitor cyanide. These results suggest that Pi concentration is a sensitive indicator of metabolic status. Moreover, we propose that live Pi imaging in C. elegans is a powerful approach to discern mechanisms that govern Pi distribution in individual cells and throughout an animal.     

纳米铁标记骨髓间质干细胞的MR研究

探讨超顺磁性氧化铁纳米粒子(Superparamagnefic iron oxide,SPIO)体外标记大鼠骨髓间质干细胞(mesenchymal stem cells,MSCs)的磁共振(magnetic resonance,MR)的成像特征.选取第5代细胞进行SPIO标记,其标记浓度为28 mg/L,选取不同的标记细胞数量,使用1.5 TMR进行T1WISE、T2WIFSE、T2WFGR扫描,测量不同扫描序列标记细胞管的信号强度改变,并进行统计学分析.细胞标记率为92%,细胞存活率为97%,MR成像显示,随着细胞数量的增多,标记细胞信号呈线性减低趋势.MR成像能敏感地显示SPIO标记的骨髓间质干细胞.     

Imaging the Intracellular Trafficking of APP with Photoactivatable GFP

Beta-amyloid (Aβ) is the major constituent of senile plaques found in the brains of Alzheimer’s disease patients. Aβ is derived from the sequential cleavage of Amyloid Precursor Protein (APP) by β and γ-secretases. Despite the importance of Aβ to AD pathology, the subcellular localization of these cleavages is not well established. Work in our laboratory and others implicate the endosomal/lysosomal system in APP processing after internalization from the cell surface. However, the intracellular trafficking of APP is relatively understudied.While cell-surface proteins are amendable to many labeling techniques, there are no simple methods for following the trafficking of membrane proteins from the Golgi. To this end, we created APP constructs that were tagged with photo-activatable GFP (paGFP) at the C-terminus. After synthesis, paGFP has low basal fluorescence, but it can be stimulated with 413 nm light to produce a strong, stable green fluorescence. By using the Golgi marker Galactosyl transferase coupled to Cyan Fluorescent Protein (GalT-CFP) as a target, we are able to accurately photoactivate APP in the trans-Golgi network. Photo-activated APP-paGFP can then be followed as it traffics to downstream compartments identified with fluorescently tagged compartment marker proteins for the early endosome (Rab5), the late endosome (Rab9) and the lysosome (LAMP1). Furthermore, using inhibitors to APP processing including chloroquine or the γ-secretase inhibitor L685, 458, we are able to perform pulse-chase experiments to examine the processing of APP in single cells.We find that a large fraction of APP moves rapidly to the lysosome without appearing at the cell surface, and is then cleared from the lysosome by secretase-like cleavages. This technique demonstrates the utility of paGFP for following the trafficking and processing of intracellular proteins from the Golgi to downstream compartments.     

Control of DNA Replication by the Nucleus/Cytoplasm Ratio in Xenopus

The nucleus/cytoplasm (N/C) ratio controls S phase dynamics in many biological systems, most notably the abrupt remodeling of the cell cycle that occurs at the midblastula transition in early Xenopus laevis embryos. After an initial series of rapid cleavage cycles consisting only of S and M phases, a critical N/C ratio is reached, which causes a sharp increase in the length of S phase as the cell cycle is reconfigured to resemble somatic cell cycles. How the N/C ratio determines the length of S phase has been a longstanding problem in developmental biology. Using Xenopus egg extracts, we show that DNA replication at high N/C ratio is restricted by one or more limiting substances. We report here that the protein phosphatase PP2A, in conjunction with its B55α regulatory subunit, becomes limiting for replication origin firing at high N/C ratio, and this in turn leads to reduced origin activation and an increase in the time required to complete S phase. Increasing the levels of PP2A catalytic subunit or B55α experimentally restores rapid DNA synthesis at high N/C ratio. Inversely, reduction of PP2A or B55α levels sharply extends S phase even in low N/C extracts. These results identify PP2A-B55α as a link between DNA replication and N/C ratio in egg extracts and suggest a mechanism that may influence the onset of the midblastula transition in vivo.     

A Transformation-induced Alteration of Cellular Membranes in Crown Gall Tumor Cells

Phospholipids were utilized as a membrane marker to test for transformation-induced alteration of cellular membranes of cultured crown gall cells of Vinca rosea L. Fully transformed cells contained less than half the amount of phospholipids (7.8 micrograms lipid P per gram fresh weight) of normal V. rosea cells (21.4 micrograms lipid P per gram fresh weight). The normal V. rosea callus cells were not significantly different (P > 0.05) in phospholipid content from partially transformed crown gall cells (20.7 micrograms lipid P per gram fresh weight). Stimulation to rapid growth of the partially transformed cells by adding higher concentrations of inorganic salts and auxin did not significantly alter their phospholipid content (23.1 micrograms lipid P per gram fresh weight). These findings suggest that the transformation process is directly responsible for an alteration of the cellular membranes and that the membrane alteration cannot be attributed to secondary effects associated with the rapid growth of these neoplastic cells.     

The cdc2Ms Kinase Is Differently Regulated in the Cytoplasm and in the Nucleus

To study a cyclin-dependent kinase (CDK) from alfalfa (Medicago sativa L.), an antibody was raised against the C-terminal 16 amino acids of the protein cdc2aMs. The cdc2Ms protein was immunopurified with this antibody and its histone kinase activity was measured. The cdc2Ms kinase is activated at the G1/S transition when phosphate-starved cells from the G0 phase re-enter the cell cycle and remain active as cells transit the S, G2, and M phases, indicating that the same CDK regulates all of these phases in alfalfa. In contrast, when cdc2Ms kinase was purified by binding to p13suc1, it was active only in the G2 and M phases. In immunoblots the C-terminal antibody detected an equal amount of the cdc2Ms protein in the cytoplasm and in the nucleus. By indirect immunofluorescence, however, the cytoplasmic form of cdc2Ms could not be found in the S phase of the cells, indicating that the epitope for the cdc2 antibody is not accessible. Binding of putative inhibitor proteins to cdc2 was shown by inactivation of purified plant CDK when cell extracts were added. Furthermore, purified CDK inhibitors, such as the mouse p27kip1 and the yeast p40sic1, blocked the purified plant CDK activity.     

A Role for the Juxtamembrane Cytoplasm in the Molecular Dynamics of Focal Adhesions

Focal adhesions (FAs) are specialized membrane-associated multi-protein complexes that link the cell to the extracellular matrix and play crucial roles in cell-matrix sensing. Considerable information is available on the complex molecular composition of these sites, yet the regulation of FA dynamics is largely unknown. Based on a combination of FRAP studies in live cells, with in silico simulations and mathematical modeling, we show that the FA plaque proteins paxillin and vinculin exist in four dynamic states: an immobile FA-bound fraction, an FA-associated fraction undergoing exchange, a juxtamembrane fraction experiencing attenuated diffusion, and a fast-diffusing cytoplasmic pool. The juxtamembrane region surrounding FAs displays a gradient of FA plaque proteins with respect to both concentration and dynamics. Based on these findings, we propose a new model for the regulation of FA dynamics in which this juxtamembrane domain acts as an intermediary layer, enabling an efficient regulation of FA formation and reorganization.     

哺乳动物核移植中供核与受体卵胞质细胞周期的相互关系

就供核与受体卵胞质细胞周期的相互关系问题进行了综述.核移植技术不管是在基础理论,还是在应用研究中都具有广泛的应用价值,但核移植的效率却很低,其根本原因是与核移植相关的许多基础理论问题尚不清楚,对这些问题的研究发现,维持重构卵核的正确倍性,并使其重新程序化是核移植成功的关键,不同的胞质受体及不同的供体细胞及其状态均对重构胚的发育有影响.