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PubMed2001

RNA commutes to work: regulation of plant gene expression by systemically transported RNA molecules.

Although long-distance movement of endogenous mRNAs in plants is well established, the functional contributions of these transported RNA molecules has remained unclear. In a recent report, Kim et al.2001 showed that systemically transported mRNA is capable of causing phenotypic change in developing tissue. Here, this finding and its significance are reviewed and discussed in detail. In addition, in order to give proper perspective, long-distance transport of other types of RNAs, e.g., RNA elicitors of post-transcriptional gene silencing and RNA genomes of plant viruses, and its possible regulation are discussed.

Biological Transport↗
PubMed1996

RNA transport to the vegetal cortex of Xenopus oocytes.

Xcat-2 RNA, a component of the germ plasm in Xenopus, localizes with the mitochondrial cloud material to the vegetal cortex in stage II oocytes. Vg1 RNA also localizes to the vegetal cortex, but later in stage III/IV oocytes, using a microtubule dependent pathway. To further analyze the mechanisms involved in RNA transport, in situ hybridization and autoradiography were used to follow the localization of endogenous Vg1 and injected Xcat-2 transcripts in stage IV oocytes. We show that Xcat-2 is competent to localize to the vegetal cortex quite independently of the mitochondrial cloud. Xcat-2 RNA appears to use the late Vg1 localization pathway, as depolymerization of microtubules by cold or nocodazole treatment prevented translocation of Xcat-2 transcripts, but did not result in the disruption of Xcat-2 anchored in the cortex. Furthermore, RNA transport was shown to be stage dependent for both Vg1 and Xcat-2 RNAs, as they did not localize in fully grown stage VI oocytes after injection. RNA sequences both required and sufficient to direct Xcat-2 to the vegetal cortex were mapped to a sequence of 150 nt immediately adjacent to the open reading frame and additional sequences at the end of the 3' untranslated region. Mapping was accomplished by injecting deletion mutant transcripts into stage IV oocytes and monitoring localization by RNase protection and autoradiography. All mutants competent for translocation were also capable of cortical anchoring, suggesting that the same signal is used for both steps. We speculate that two separate RNA pathways evolved during the course of Xenopus oogenesis. One pathway, specialized for the transport of germ plasm by way of the mitochondrial cloud, occurs early to ensure the segregation of the germ cell lineage. The other, late, pathway may serve as the more general transport system for localizing RNAs involved in somatic cell differentiation.

Animals↗
PubMed1990

Role of cytosol in the stimulation of RNA transport in vitro during cardiac hypertrophy in rats.

The 100,000 g supernatant isolated from hypertrophic hearts on fractionation by (NH4)2SO4 and DEAE-cellulose chromatography showed an enhanced RNA-transport activity when incubated with isolated nuclei from sham-operated hearts in vitro. Proteins of Mr 73,000, 68,000, 43,000 and 32,000 are enriched in the DEAE-cellulose fractions exhibiting maximal transport activity, and they are phosphorylatable. Pretreatment of the cytosol with antibodies to the Mr-68,000 and -32,000 proteins decreases the transport activity of the cytosol from 14% to 4.25%. Proteins of Mr 73,000, 68,000, 43,000 and 32,000 are translocated from the cytosol to the nuclear envelope under conditions of RNA transport in vitro. Our results here suggest that at least two of these proteins, those of Mr 68,000 and 32,000, play an indispensible role in the nucleocytoplasmic RNA transport in vitro. By making use of a specific myosin heavy-chain B-gene probe and hybridization, we have also shown the effect of cytosol on the transport of myosin heavy-chain mRNA from nucleus to cytosol.

Ammonium Sulfate↗
PubMed2005

RNA transport and local control of translation.

In eukaryotes, the entwined pathways of RNA transport and local translational regulation are key determinants in the spatio-temporal articulation of gene expression. One of the main advantages of this mechanism over transcriptional control in the nucleus lies in the fact that it endows local sites with independent decision-making authority, a consideration that is of particular relevance in cells with complex cellular architecture such as neurons. Localized RNAs typically contain codes, expressed within cis-acting elements, that specify subcellular targeting. Such codes are recognized by trans-acting factors, adaptors that mediate translocation along cytoskeletal elements by molecular motors. Most transported mRNAs are assumed translationally dormant while en route. In some cell types, especially in neurons, it is considered crucial that translation remains repressed after arrival at the destination site (e.g., a postsynaptic microdomain) until an appropriate activation signal is received. Several candidate mechanisms have been suggested to participate in the local implementation of translational repression and activation, and such mechanisms may target translation at the level of initiation and/or elongation. Recent data indicate that untranslated RNAs may play important roles in the local control of translation.

Animals↗
PubMed1989

[Age-related characteristics of RNA transport through the nuclear membrane].

The effect of cytosol and ATP-regenerating system on RNA, transport was studied in isolated liver nuclei of adult and old rats. The stimulating effect of cytosol was found not to depend on the age of animals. The release of RNA from old rat liver nuclei activated by the ATP-regenerating system was more expressed compared to adult rats. It is assumed that the age changes of energy-delivering system of the RNA transport through nuclear membrane may be conditioned by the deficit of endogenous energetic substrates in the hepatic cells of old animals.

Adenosine Triphosphate↗
PubMed1991

The HIV-1 Rev protein: a model system for coupled RNA transport and translation.

The impact of the Rev protein of the human immunodeficiency virus type 1 (HIV-1) on RNA transport, intranuclear RNA distribution, and gene expression was examined for two Rev-dependent expression systems by means of fluorescence in situ hybridization, immunofluorescence, S1 nuclease protection, and functional assays. In the pgTat expression system, which utilizes authentic HIV-1 splice signals, unspliced mRNA remained entrapped in the nucleus in the absence of Rev and was exported to the cytoplasm in its presence, consistent with published findings. In the pSVAR expression system, significant levels of mRNA were found in the nucleus and cytoplasm in both the presence and absence of Rev, but only in the presence of Rev was mRNA translated into protein. The presence of cytoplasmic untranslated mRNA in the absence of Rev was demonstrated by in situ hybridization analysis of individual cells as well as by S1 nuclease analysis of cell populations. The results indicate that Rev has the potential to affect translation as well as transport, suggesting the possibility that cellular mechanisms exist whereby the translational efficiency of an mRNA may be affected by the manner in which it is transported from the nucleus. Fluorescence hybridization also provided high-resolution visualization of the intranuclear distribution of RNAs containing the Rev response element. This demonstrated for both expression systems that mRNA was not highly localized in tracks or around the nucleolus in the presence or absence of Rev, a nucleolar protein, but was more widely distributed throughout the nucleus. In pgTat transfectants, HIV-1 RNA often became localized in 5 to 20 discrete large intranuclear clusters in the presence of Rev, the potential significance of which is discussed.

Biological Transport↗
PubMed1982

The fluidity of the nuclear envelope lipid does not affect the rate of nucleocytoplasmic RNA transport in mammalian liver.

The effects of in vitro and in vivo modifications of nuclear envelope lipid on DNa leakage and on ATP-stimulated RNA release from isolated rat liver nuclei were investigated. The modifications included corn-oil feeding of the animals to alter the fatty acid composition of the lipids, phospholipase treatment of the isolated nuclei, and extraction of the total lipid with Triton X-100. Significant changes in lipid composition and approximate order parameter values of the spin-label 5-doxylstearate resulted, but there was no significant effect on RNA transport rate. It was concluded that the nuclear envelope lipid does not play any important part in nucleocytoplasmic RNA transport in mammalian liver.

Animals↗
PubMed1978

Activation energy for RNA transport from isolated rat liver nuclei.

The temperature dependence of ATP-enhanced RNA delivery from rat liver nuclei to a surrogate cytoplasm was investigated. Examination of linear-rate data on Arrhenius graphs of 1/T vs. log (% RNA delivered per min) revealed an activation energy of 12.5--13 kcal/mol. When data derived from longer incubation periods was displayed on Arrhenius graphs, we observed a discontinuous graph--two distinct linear segments with slopes of differing sign which intersected near 20 degrees C. It was demonstrated that this discontinuity was not due to lipid phase transition in the nuclear membranes and that its position depended upon treatment of the nuclei and upon additives to the incubation mixtures. The decline in transport apparent in the upper-temperature domain on 20-min Arrhenius graphs was shown to be based on the diffusion of transported macromolecular RNA back into the nucleus--a process greatly amplified by the rapidity of transport in this domain. The large net inward diffusion, in concert with significantly differing activation energies for RNA transport and passive diffusion, suggests that the process of nucleocytoplasmic RNA transport is not diffusion driven. Our data have established that an integral parameter of RNA transport (namely, the activation energy) remains unchanged in various in vitro manipulations.

Animals↗
PubMed1990

Evidence for involvement of a nuclear envelope-associated RNA helicase activity in nucleocytoplasmic RNA transport.

It seems well established that translocation of at least some mRNAs through the nuclear pore is (1) an energy-dependent process, and (2) dependent on the presence of the poly(A) segment attached to most mRNA species. We describe that RNA helicase (RNA duplex unwindase) activity is present in a nuclear envelope (NE) preparation, which also appears to be involved in nucleocytoplasmic RNA transport. This activity unwinds RNA: RNA hybrids. The helicase has a pH optimum of 7.5 and a temperature optimum of 30 degrees C. Applying the sealed NE vesicle system, it was shown that duplex RNA species are readily released from the vesicles in an unidirectional manner, in contrast to single-stranded RNA, which is much slower transported into the extravesicular space. Attachment of a poly(A) segment to the RNA duplex additionally increases the efflux rate of this RNA. Efflux of duplex RNA but not efflux of single-stranded RNA was strongly inhibited by formycin B 5'-triphosphate. Our results suggest that, besides poly(A), duplex structures, if present in a given RNA, modulate and control the export of RNA.

Animals↗
PubMed1982

[RNA transport from isolated nuclei of cultured Djungarian hamster cells].

The in vitro system of RNA transport containing isolated nuclei of Djungarian hamster cells transformed by SV-40 virus was studied. A functional test for cytoplasmic contaminations of the nuclei was proposed. The release of the newly synthesized RNA was found to be dependent on the duration of incubation, temperature and pH of the incubation medium as well as on the presence of spermine, spermidine, dithiothreitol, Mg2+, EDTA, exogenous RNA, nucleoside triphosphates and cytosol. The results obtained indicate that RNA release is an active process with activation energy of 12 kcal/mol. ATP, GTP, CTP and UTP have equal ability to serve as energy sources for the release of RNA. The nucleoside triphosphatase activity of the nuclei was the same in the presence of these four nucleoside triphosphates.

Animals↗
PubMed2005

Identification of translocatable RNA-binding phloem proteins from melon, potential components of the long-distance RNA transport system.

Phloem proteins (P-proteins) are an enigmatic group of proteins present in most angiosperm species. The best characterized P-proteins (PP1 and PP2) are synthesized in companion cells, transported into sieve elements via pore plasmodesmata and translocated through the plant. Characteristics such as long-distance translocation, RNA-binding activity and capacity of increasing plasmodesmata exclusion size suggest that certain phloem proteins could be involved in RNA transport within the plant, forming translocatable ribonucleoprotein complexes with endogenous or pathogenic RNAs. Long-distance movement of RNA through the phloem is a process known to occur, but both the mechanisms involved and the components constituting this potential information network remain unclear. Here, we demonstrate that several melon phloem proteins have a wide RNA-binding activity. Serological assays strongly suggest that one of these proteins is the melon phloem protein 2 (CmmPP2). Mass spectrometry analysis undoubtedly identifies another one as the recently characterized melon phloem lectin (CmmLec17). Grafting experiments demonstrate that the CmmLec17 is a translocatable phloem protein, able to move through intergeneric grafts from melon to pumpkin. Translocatability and RNA-binding activity was also demonstrated for an uncharacterized protein of approximately 14 kDa. In light of these results the possible involvement of these phloem proteins in the long-distance transport of melon RNAs is discussed.

Amino Acid Sequence↗
PubMed1978

[RNA transport from rat liver cell nuclei in vitro. Release of rapidly labeled RNA from isolated nuclei in a cell-free system in the presence of RNAse affectors].

A cell-free system was developed and characterized, which supported RNA release from isolated rat liver cell nuclei. The RNA release in the system seemed to be dependent on the presence of ATP as an evergy source and of dialized cytosol as far as on the temperature level in the incubation mixture. In vitro effects of a number of RNase affectors from cytoplasm and of related exogenous compounds on the RNA release were studied. It was shown that RNase inhibitors such as heparin, PVS and rat liver cytoplasmic RNA were capable to stimulate the RNA release, while the natural inhibitor from liver cytosol failed to influence the RNA relase. Spermidine and PCMB lowered the rate of RNA release from nuclei. The results are discussed in connection with possible role of nuclear RNases and cytoplasmic factors in nucleocytoplasmic transport of RNA.

Adenosine Triphosphate↗
PubMed2004

RNA transport (partly) revealed!

Specific mRNAs are transported to dendrites where their translation may modify synaptic plasticity. In this issue of Neuron, Kanai et al. use affinity chromatography and mass spectrometry to identify a large number of new factors that associate with kinesin, a molecular motor, and employ siRNA technology to demonstrate their importance for RNA transport in neurons.

Animals↗
PubMed2006

RNA-binding motif protein 15 binds to the RNA transport element RTE and provides a direct link to the NXF1 export pathway.

Retroviruses/retroelements provide tools enabling the identification and dissection of basic steps for post-transcriptional regulation of cellular mRNAs. The RNA transport element (RTE) identified in mouse retrotransposons is functionally equivalent to constitutive transport element of Type D retroviruses, yet does not bind directly to the mRNA export receptor NXF1. Here, we report that the RNA-binding motif protein 15 (RBM15) recognizes RTE directly and specifically in vitro and stimulates export and expression of RTE-containing reporter mRNAs in vivo. Tethering of RBM15 to a reporter mRNA showed that RBM15 acts by promoting mRNA export from the nucleus. We also found that RBM15 binds to NXF1 and the two proteins cooperate in stimulating RTE-mediated mRNA export and expression. Thus, RBM15 is a novel mRNA export factor and is part of the NXF1 pathway. We propose that RTE evolved as a high affinity RBM15 ligand to provide a splicing-independent link to NXF1, thereby ensuring efficient nuclear export and expression of retrotransposon transcripts.

Alternative Splicing↗
PubMed1982

Effect of colchicine on mammalian liver nuclear envelope and on nucleo-cytoplasmic RNA transport.

The binding of colchicine to nuclear envelopes was studied in order to elucidate the mechanism whereby this compound inhibits nucleocytoplasmic RNA transport. The results suggest that a single class of colchicine-binding site (dissociation constant=approx. 0.7 mM, concentration=approx. 330 nmol colchicine/mg protein) is localised in the nuclear periphery (pore-lamina) and that binding to these sites effects a constriction of the pore-complexes with concomitant inhibition of RNA egress and disordering of the nuclear membrane phospholipid bilayers.

Animals↗
PubMed1979

Altered RNA transport without derepression in a rat kidney tumor induced by dimethylnitrosamine.

RNA/DNA hybridization in the presence of competing RNA was used to study transcription and transport of RNA from the nucleus to the cytoplasm in a rat renal tumor induced by a single intraperitoneal injection of dimethylnitrosamine (DMN). Neither repression nor derepression of transcription of repetitive DNA can be detected in this tumor, but transcripts of all active families of such sequences are found in the tumor cytoplasm. This is the pattern of RNA change found in the chemically-induced hepatocellular carcinomas and contrasts with the pattern of virus-induced renal tumors in which both altered transport and derepression of host repetitive sequences have been demonstrated. The alteration of RNA transport is nearly complete in the kidney only two days after the above treatment, but there is no such alteration detectable in the kidney after nine days of feeding a liver carcinogen which is not carcinogenic to kidneys. This data supports the significance and specificity of the loss of ability to restrict certain RNA sequences to the nucleus early during malignant transformation.

Animals↗
PubMed1975

[Rna transport from the nucleus to the cytoplasm in Acetabularia mediterranea].

The biosynthesis of nuclear RNA, its transport from the nucleus to the cytoplasm and distribution in the cytoplasm were studied in Acetabularia mediterranea under different light conditions. It was shown that the nuclear RNA incorportate 3H-uracil more rapidly in the darkness and the transport of labeled RNA from the nucleus slowed down after the transfer of plants in the cold medium in the darkness. To study the distribution of nuclear RNA in the cytoplasm, the 3H-uracil labeled nuclei were transplanted in the rhizoids of unlabeled plants, the dikaryons obtained were kept for different time in the light and in the darkness and the content of 3H-RNA was determined in different stem regions. It was shown that the transport of 3H-RNA in the cytoplasm is slowed down in the darkness and it is distributed by the basal-apical gradient. RNA is rapidly accumulated in the apical stem zone in the light and redistributed afterwards in the basal stem zones. The problem of relationship between the polarity and nuclear RNA distribution in Acetabularia is discussed.

Acetabularia↗
PubMed2002

Intramolecular complementing mutations in tobacco mosaic virus movement protein confirm a role for microtubule association in viral RNA transport.

The movement protein (MP) of Tobacco mosaic virus (TMV) facilitates the cell-to-cell transport of the viral RNA genome through plasmodesmata (Pd). A previous report described the functional reversion of a dysfunctional mutation in MP (Pro81Ser) by two additional amino acid substitution mutations (Thr104Ile and Arg167Lys). To further explore the mechanism underlying this intramolecular complementation event, the mutations were introduced into a virus derivative expressing the MP as a fusion to green fluorescent protein (GFP). Microscopic analysis of infected protoplasts and of infection sites in leaves of MP-transgenic Nicotiana benthamiana indicates that MP(P81S)-GFP and MP(P81S;T104I;R167K)-GFP differ in subcellular distribution. MP(P81S)-GFP lacks specific sites of accumulation in protoplasts and, in epidermal cells, exclusively localizes to Pd. MP(P81S;T104I;R167K)-GFP, in contrast, in addition localizes to inclusion bodies and microtubules and thus exhibits a subcellular localization pattern that is similar, if not identical, to the pattern reported for wild-type MP-GFP. Since accumulation of MP to inclusion bodies is not required for function, these observations confirm a role for microtubules in TMV RNA cell-to-cell transport.

Biological Transport↗