This work was supported by grants from the National Science and Engineering Research Council of Canada to X.A.C. and A.F.P.

1. Preparation of Materials for Extraction
<ol>
	<li>Preparation of Cells
	<ol>
		<li>Seed tissue culture cells on acid-treated coverslips for at least one day prior to the experiment. We use COS-7 or U2OS, as these two cell lines exhibit robust production of secreted protein and have a well defined ER. Note that to achieve high extraction efficiency, cells should not exceed 80% confluency on the coverslip on the day of the experiment.</li>
		<li>If a particular exogenous mRNA is being investigated, cells are transfect...

<ol>
	<li>Walter, P., Ibrahimi, I., Blobel, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translocation+of+proteins+across+the+endoplasmic+reticulum.+I.+Signal+recognition+protein+(SRP)+binds+to+in-vitro-assembled+polysomes+synthesizing+secretory+protein.">Translocation of proteins across the endoplasmic reticulum. I. Signal recognition protein (SRP) binds to in-vitro-assembled polysomes synthesizing secretory protein.</a> J. Cell Biol. 91, 545-550 (1981).</li><li>Walter, P., Blobel, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Translocation+of+proteins+across+the+endoplasmic+reticulum.+II.+Signal+recognition+protein+(SRP)+mediates+the+selective+binding+to+microsomal+membranes+of+in-vitro-assembled+polysomes+synthesizing+secretory+protein.">Translocation of proteins across the endoplasmic reticulum. II. Signal recognition protein (SRP) mediates the selective binding to microsomal membranes of in-vitro-assembled polysomes synthesizing secretory protein.</a> J. Cell Biol. 91, 551-556 (1981).</li><li>Grlich, D., Prehn, S., Hartmann, E., Kalies, K. U., Rapoport, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+mammalian+homolog+of+SEC61p+and+SECYp+is+associated+with+ribosomes+and+nascent+polypeptides+during+translocation.">A mammalian homolog of SEC61p and SECYp is associated with ribosomes and nascent polypeptides during translocation.</a> Cell. 71, 489-503 (1992).</li><li>Grlich, D., Rapoport, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+translocation+into+proteoliposomes+reconstituted+from+purified+components+of+the+endoplasmic+reticulum+membrane.">Protein translocation into proteoliposomes reconstituted from purified components of the endoplasmic reticulum membrane.</a> Cell. 75, 615-630 (1993).</li><li>Milcarek, C., Penman, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane-bound+polyribosomes+in+HeLa+cells:+association+of+polyadenylic+acid+with+membranes.">Membrane-bound polyribosomes in HeLa cells: association of polyadenylic acid with membranes.</a> J. Mol. Biol. 89, 327-338 (1974).</li><li>Lande, M. A., Adesnik, M., Sumida, M., Tashiro, Y., Sabatini, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+association+of+messenger+RNA+with+microsomal+membranes+in+human+diploid+fibroblasts.">Direct association of messenger RNA with microsomal membranes in human diploid fibroblasts.</a> J. Cell Biol. 65, 513-528 (1975).</li><li>Cardelli, J., Long, B., Pitot, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+association+of+messenger+RNA+labeled+in+the+presence+of+fluoroorotate+with+membranes+of+the+endoplasmic+reticulum+in+rat+liver.">Direct association of messenger RNA labeled in the presence of fluoroorotate with membranes of the endoplasmic reticulum in rat liver.</a> J. Cell Biol. 70, 47-58 (1976).</li><li>Adesnik, M., Lande, M., Martin, T., Sabatini, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retention+of+mRNA+on+the+endoplasmic+reticulum+membranes+after+in+vivo+disassembly+of+polysomes+by+an+inhibitor+of+initiation.">Retention of mRNA on the endoplasmic reticulum membranes after in vivo disassembly of polysomes by an inhibitor of initiation.</a> J. Cell Biol. 71, 307-313 (1976).</li><li>Kruppa, J., Sabatini, D. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Release+of+poly+A(+)+messenger+RNA+from+rat+liver+rough+microsomes+upon+disassembly+of+bound+polysomes.">Release of poly A(+) messenger RNA from rat liver rough microsomes upon disassembly of bound polysomes.</a> J. Cell Biol. 74, 414-427 (1977).</li><li>Adesnik, M., Maschio, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Segregation+of+specific+classes+of+messenger+RNA+into+free+and+membrane-bound+polysomes.">Segregation of specific classes of messenger RNA into free and membrane-bound polysomes.</a> Eur. J. Biochem. 114, 271-284 (1981).</li><li>Cui, X. A., Zhang, H., Palazzo, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=p180+Promotes+the+Ribosome-Independent+Localization+of+a+Subset+of+mRNA+to+the+Endoplasmic+Reticulum.">p180 Promotes the Ribosome-Independent Localization of a Subset of mRNA to the Endoplasmic Reticulum.</a> PLoS Biol. 10, e1001336 (2012).</li><li>Pestka, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibitors+of+ribosome+functions.">Inhibitors of ribosome functions.</a> Annu. Rev. Microbiol. 25, 487-562 (1971).</li><li>Fresno, M., Jimnez, A., Vzquez, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+translation+in+eukaryotic+systems+by+harringtonine.">Inhibition of translation in eukaryotic systems by harringtonine.</a> Eur. J. Biochem. 72, 323-330 (1977).</li><li>Weeks, D. P., Baxter, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Specific+inhibition+of+peptide-chain+initiation+by+2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide.">Specific inhibition of peptide-chain initiation by 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide.</a> Biochemistry. 11, 3060-3064 (1972).</li><li>Ingolia, N. T., Lareau, L. F., Weissman, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ribosome+profiling+of+mouse+embryonic+stem+cells+reveals+the+complexity+and+dynamics+of+mammalian+proteomes.">Ribosome profiling of mouse embryonic stem cells reveals the complexity and dynamics of mammalian proteomes.</a> Cell. 147, 789-802 (2011).</li><li>Lerner, R. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Partitioning+and+translation+of+mRNAs+encoding+soluble+proteins+on+membrane-bound+ribosomes.">Partitioning and translation of mRNAs encoding soluble proteins on membrane-bound ribosomes.</a> RNA. 9, 1123-1137 (2003).</li><li>Adam, S. A., Marr, R. S., Gerace, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+protein+import+in+permeabilized+mammalian+cells+requires+soluble+cytoplasmic+factors.">Nuclear protein import in permeabilized mammalian cells requires soluble cytoplasmic factors.</a> J. Cell Biol. 111, 807-816 (1990).</li><li>Reuter, J. S., Mathews, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RNAstructure:+software+for+RNA+secondary+structure+prediction+and+analysis.">RNAstructure: software for RNA secondary structure prediction and analysis.</a> BMC Bioinformatics. 11, 129 (2010).</li><li>Lcuyer, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Global+analysis+of+mRNA+localization+reveals+a+prominent+role+in+organizing+cellular+architecture+and+function.">Global analysis of mRNA localization reveals a prominent role in organizing cellular architecture and function.</a> Cell. 131, 174-187 (2007).</li><li>Lcuyer, E., Yoshida, H., Krause, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Global+implications+of+mRNA+localization+pathways+in+cellular+organization.">Global implications of mRNA localization pathways in cellular organization.</a> Curr. Opin. Cell Biol. 21, 409-415 (2009).</li><li>Gueroussov, S., Tarnawsky, S. P., Cui, X. A., Mahadevan, K., Palazzo, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+mRNA+nuclear+export+kinetics+in+mammalian+cells+by+microinjection.">Analysis of mRNA nuclear export kinetics in mammalian cells by microinjection.</a> J Vis Exp. 46, e2387 (2010).</li></ol>

The localization of mRNAs to various subcellular sites, through the interaction of transcripts with mRNA localization proteins, is a widespread phenomenon important for the proper sorting of proteins to their final destination, and for the fine tuning of gene expression to the local requirements of a subcellular region19,20.
Using the assay described here, we revisited the question of whether mRNAs that encode secretory proteins can be maintained on the ER in the presence or absence...

In eukaryotes, mRNA encoding secreted and membrane proteins can be targeted to the ER co-translationally by the signal recognition particle1,2 and can be maintained on the ER via the direct interactions between ribosomes and translocons during the translation3,4. However, whether mRNAs can be targeted and maintained on the ER independent of either ribosomes or translation was unclear until very recently. Previous studies attempted to address whether there is translation-independent mRNA association with the ER using cellular fractionation techniques. Because harsh chemical conditions were required to disassociate ribosomes from ER derived vesicles, which might disrupt the potentially delicate mRNA-ER association, these studies were inconclusive, providing evidence for5-8 and against9,10 ribosomal-independent anchoring of mRNA to the ER.
To circumvent these problems we have developed a protocol to isolate and image ER-bound mRNAs. This procedure involves a mild extraction treatment, which effectively removes all the cytoplasmic content of the cell (including non ER-bound mRNAs) while simultaneously preserving the ER morphology and all of its associated molecules. Using this protocol we have demonstrated that a subset of mRNAs are targeted and then maintained on the ER independently of ribosomes or translation11.

visualization of endoplasmic reticulum localized mrnas in mammalian cells

In eukaryotes, most of the messenger RNAs (mRNAs) that encode secreted and membrane proteins are localized to the surface of the endoplasmic reticulum (ER). However, the visualization of these mRNAs can be challenging. This is especially true when only a fraction of the mRNA is ER-associated and their distribution to this organelle is obstructed by non-targeted (i.e. "free") transcripts. In order to monitor ER-associated mRNAs, we have developed a method in which cells are treated with a short exposure to a digitonin extraction solution that selectively permeabilizes the plasma membrane, and thus removes the cytoplasmic contents, while simultaneously maintaining the integrity of the ER. When this method is coupled with fluorescent in situ hybridization (FISH), one can clearly visualize ER-bound mRNAs by fluorescent microscopy. Using this protocol the degree of ER-association for either bulk poly(A) transcripts or specific mRNAs can be assessed and even quantified. In the process, one can use this assay to investigate the nature of mRNA-ER interactions.

To determine the percentage of mRNA that is ER-associated, COS-7 cells that were transfected with plasmids that contained the placental alkaline phosphatase (ALPP) or cytochrome P450-8B1 (CYP8B1) were either extracted with digitonin and then fixed, or directly fixed (see Figure 1, compare "Unextracted Ctrl" to "Extracted Ctrl"). The non-nuclear fluorescence was quantified in both samples and the fraction of ER-associated mRNA was calculated (Figure 2)....

Watch this Scientific Journal Video about Visualization of Endoplasmic Reticulum Localized mRNAs in Mammalian Cells at JoVE.com

Visualization of Endoplasmic Reticulum Localized mRNAs in Mammalian Cells

Here we describe a method to visualize endoplasmic reticulum-associated mRNAs in mammalian tissue culture cells. This technique involves the selective permeabilization of the plasma membrane with digitonin to remove cytoplasmic contents followed by fluorescent in situ hybridization to detect either bulk poly(A) mRNA or specific transcripts.

In eukaryotes, most of the messenger RNAs (mRNAs) that encode secreted and membrane proteins are localized to the surface of the endoplasmic reticulum ...

visualization-endoplasmic-reticulum-localized-mrnas-mammalian

Research

JoVE Journal

Biology

14.2K visualizações.  University of Toronto. Descrevemos aqui um método para visualizar retículo endoplasmático associadas mRNAs em células de cultura de mamífero de tecidos. Esta técnica envolve a permeabilização selectiva da membrana plasmática com digitonina para remover conteúdo citoplasmático seguido fluorescente In situ Hibridação para detectar ou poli granel (A) mRNA ou transcritos específicos.