The authors are grateful to Fondazione Filarete for its help and support in the publication of this article. We would also like to thank Centro Europeo di Nanomedicina for the use of the TECNAI G2 transmission electron microscope.

1. Plasmid, Cell Culture, and Transfection with ER Fluorescent Proteins
<ol>
	<li>The plasmid used in this study consists of an enhanced version of GFP fused at its C-terminus to the tail region of the ER isoform of rat cytochrome b(5) (abbreviated here as b(5)) via a linker sequence. The tail region contains the entire sequence (Pro94-Asp134) that remains membrane associated after the trypsin cleavage of native b(5), including the 17-residue TMD (Transmembrane domain), flanked by upstream and downstream polar sequences (UPS and DPS). The linker consists of the myc epitope followed by [(Gly)4Ser]3, and the entire cDNA is inserted into the Hind3-Xba1 sites of the mammalian expression vector pCDNA3. The details of the construction of this plasmid have been described in a previous publication in which it is referred to as GFP-ER16.</li>
	<li>Grow COS-7 cells in Dulbecco&#39;s Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum, 2 mM L-glutamine, 1% penicillin/streptomycin in an incubator at 37 &#176;C and 10% CO2.</li>
	<li>Transfection. Plate 3 x 105 cells on a round glass coverslip in a 6-well plate and, on the following day, transfect with the JetPEI system as described by the manufacturer. Note that the optimal JetPEI/DNA ratio has been tested in order to establish the maximum transfection efficiency depending on the plasmid and cell line used: in our case, a JetPEI:DNA ratio of 2:1 leads to 70-80% transfection efficiency.</li>
</ol>
2. Live Fluorescence Scanning Confocal Microscopy
<ol>
	<li>Live-cell imaging. Put the coverslip on which the transfected cells were seeded into a steel culture cell chamber for 24 mm coverslips filled with DMEM w/o phenol red, supplemented with 10% FBS, 2 mM L-glutamine, 1% pen/strep, 25 mM HEPES, 50 &#956;g/ml cycloheximide and 1:100 OxyFluor to prevent the samples from photobleaching. An SP5 confocal microscope equipped with a temperature-controlled CO2 incubator (37 &#176;C and 5% CO2) is used for live cell imaging experiments, with dGFP-ER being visualized using a 488 nm laser and a 525/50 band pass emission filter.</li>
	<li>Fluorescence recovery after photobleaching (FRAP). Draw a region of interest (ROI), corresponding to an OSER structure, and bleach it using 20 iterations and a combination of 488 nm (100% of a 30 mW Argon laser, corresponding to 5.5-6 &#956;W at the sample) and 405 nm (60% of a 30 mW Diode 405 laser, corresponding to 11.6 &#956;W at the sample) lasers which, in our experience, leads to efficient and rapid photobleaching.</li>
	<li>Record the recovery of fluorescence in the bleached ROIs by taking a single frame every 10 sec for 10 min (pixel time = 1.61 &#956;sec/px).</li>
	<li>Fluorescence loss in photobleaching (FLIP). Draw a ROI corresponding to an OSER structure, and bleach as described above. The bleaching is repeated every 30 sec, and post-bleaching images are recorded every 10 sec for 30 min (pixel time = 1.61 &#956;sec/px).</li>
	<li>FRAP and FLIP analysis. All of the images are analyzed using ImageJ software (<a href="http://rsbweb.nih.gov/ij/download.html" target="_blank">http://rsbweb.nih.gov/ij/download.html</a>). In the FRAP experiments, the fluorescence recovery of the bleached ROI is measured over time and normalized to the total fluorescence of bleached cell, which is always checked to be constant over time.</li>
	<li>For the FLIP experiments, draw an ROI outside the bleached OSER and covering the whole cell. Measure its fluorescence intensity over time and normalize to the fluorescence levels of an ROI drawn on an unbleached cell in order to correct for any decrease in fluorescence caused by the imaging itself.</li>
	<li>In all of the experiments, subtracted the background signal (determined in an area outside the cells) from the fluorescent intensities of the ROIs. Finally, plot the results using GraphPad Prism software.</li>
</ol>
3. Ultrastructural Analysis by Means of Transmission Electron Microscopy
Given the toxicity of many of the reagents, all of the procedures should be carried out wearing an appropriate lab. coat and gloves under a fume hood.
<ol>
	<li>After removing the coverslip from the Petri dish, fix the remaining cells grown on the bottom of the dish as a monolayer using filtered 2% glutaraldehyde in 0.1 M cacodylate buffer, pH 7.4, for 10 min at room temperature.</li>
	<li>Scrape the cells using a Teflon scraper and transfer them into 1.5 ml Eppendorf tubes. Pellet the cells by means of centrifugation at 9,000 g for 10 min. Remove the supernatant, add fresh fixative, and leave overnight at 4 &#176;C.</li>
	<li>Wash the pellets with the buffer, then post-fix with a solution of 1% osmium tetroxide in cacodylate buffer for 1 hr at room temperature.</li>
	<li>Rinse with MilliQ water, and en bloc stain with 1% uranyl acetate in distilled water for between 20-60 min.</li>
	<li>Dehydrate the samples in increasing ethanol series (70%, 80%, 90%, 100%, and 100% for 10 min each), and wash briefly twice in propylene oxide (15 min each).</li>
	<li>Infiltrate the samples in a mixture of propylene oxide + Epon (1:1) (from 2 hr to overnight).</li>
	<li>Embed in Epon epoxy resin cured at 60 &#176;C for at least 24 hr.</li>
	<li>Section the manually trimmed resin blocs using an ultramicrotome LEICA UC6 equipped with a 45&#176; diamond knife to obtain sections with a thickness of 60-70 nm. Collect the sections on 300 mesh copper grids.</li>
	<li>Stain the sections on the grid with a saturated solution of uranyl acetate (20 min) and lead citrate (7 min), thoroughly wash the grids by immersing them in bi-distilled filtered water, and allow them to dry at room temperature.</li>
	<li>The stained grids are observed using a TECNAI G2 transmission electron microscope, and the images are captured using a bottom-mounted CCD camera at different final magnifications (generally ranging from 6,000-39,000X).</li>
</ol>

<ol>
	<li>Fasana, 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=A+VAPB+mutant+linked+to+amyotrophic+lateral+sclerosis+generates+a+novel+form+of+organized+smooth+endoplasmic+reticulum.">A VAPB mutant linked to amyotrophic lateral sclerosis generates a novel form of organized smooth endoplasmic reticulum.</a> FASEB J. 24, 1419-1430 (2010).</li><li>Borgese, N., Francolini, M., Snapp, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endoplasmic+reticulum+architecture:+structures+in+flux.">Endoplasmic reticulum architecture: structures in flux.</a> Curr. Opin. Cell Biol. 18, 358-364 (2006).</li><li>Ronchi, P., Colombo, S., Francolini, M., Borgese, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transmembrane+domain-dependent+partitioning+of+membrane+proteins+within+the+endoplasmic+reticulum.">Transmembrane domain-dependent partitioning of membrane proteins within the endoplasmic reticulum.</a> J. Cell Biol. 181, 105-118 (2008).</li><li>Lippincott-Schwartz, J., Snapp, E., Kenworthy, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studying+protein+dynamics+in+living+cells.">Studying protein dynamics in living cells.</a> Nat. Rev. Mol. Cell Biol. 2, 444-456 (2001).</li><li>Lee, M. C., Miller, E. A., Goldberg, J., Orci, L., Schekman, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bi-directional+protein+transport+between+the+ER+and.">Bi-directional protein transport between the ER and.</a> 20, 87-123 (2004).</li><li>Snapp, E. L., 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=Formation+of+stacked+ER+cisternae+by+low+affinity+protein+interactions.">Formation of stacked ER cisternae by low affinity protein interactions.</a> J. Cell Biol. 163, 257-269 (2003).</li><li>Papiani, G., 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=Restructured+endoplasmic+reticulum+generated+by+mutant+amyotrophic+lateral+sclerosis-linked+VAPB+is+cleared+by+the+proteasome.">Restructured endoplasmic reticulum generated by mutant amyotrophic lateral sclerosis-linked VAPB is cleared by the proteasome.</a> J. Cell Sci. 125, 3601-3611 (2012).</li><li>Almsherqi, Z. A., Kohlwein, S. D., Deng, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cubic+membranes:+a+legend+beyond+the+Flatland*+of+cell+membrane+organization.">Cubic membranes: a legend beyond the Flatland* of cell membrane organization.</a> J. Cell Biol. 173, 839-844 (2006).</li><li>Federovitch, C. M., Ron, D., Hampton, R. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dynamic+ER:+experimental+approaches+and+current+questions.">The dynamic ER: experimental approaches and current questions.</a> Curr. Opin. Cell Biol. 17, 409-414 (2005).</li><li>Takei, K., Mignery, G. A., Mugnaini, E., Sudhof, T. C., De Camilli, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inositol+1,4,5-trisphosphate+receptor+causes+formation+of+ER+cisternal+stacks+in+transfected+fibroblasts+and+in+cerebellar+Purkinje+cells.">Inositol 1,4,5-trisphosphate receptor causes formation of ER cisternal stacks in transfected fibroblasts and in cerebellar Purkinje cells.</a> Neuron. 12, 327-342 (1994).</li><li>Feldman, D., Swarm, R. L., Becker, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrastructural+study+of+rat+liver+and+liver+neoplasms+after+long-term+treatment+with+phenobarbital.">Ultrastructural study of rat liver and liver neoplasms after long-term treatment with phenobarbital.</a> Cancer Res. 41, 2151-2162 (1981).</li><li>Sprocati, T., Ronchi, P., Raimondi, A., Francolini, M., Borgese, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+and+reversible+restructuring+of+the+endoplasmic+reticulum+induced+by+PDMP+in+cultured+cells.">Dynamic and reversible restructuring of the endoplasmic reticulum induced by PDMP in cultured cells.</a> J. Cell Sci. 119, 3249-3260 (2006).</li><li>Costantini, L. M., Fossati, M., Francolini, M., Snapp, E. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessing+the+tendency+of+fluorescent+proteins+to+oligomerize+under+physiologic+conditions.">Assessing the tendency of fluorescent proteins to oligomerize under physiologic conditions.</a> Traffic. 13, 643-649 (2012).</li><li>Pyszniak, A. M., Welder, C. A., Takei, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+surface+distribution+of+high-avidity+LFA-1+detected+by+soluble+ICAM-1-coated+microspheres.">Cell surface distribution of high-avidity LFA-1 detected by soluble ICAM-1-coated microspheres.</a> J. Immunol. 152, 5241-5249 (1994).</li><li>Taylor, J. P., Hardy, J., Fischbeck, K. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toxic+proteins+in+neurodegenerative+disease.">Toxic proteins in neurodegenerative disease.</a> Science. 296, 1991-1995 (2002).</li><li>Winklhofer, K. F., Tatzelt, J., Haass, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+two+faces+of+protein+misfolding:+gain-+and+loss-of-function+in+neurodegenerative+diseases.">The two faces of protein misfolding: gain- and loss-of-function in neurodegenerative diseases.</a> EMBO J. 27, 336-349 (2008).</li><li>Borgese, N., Gazzoni, I., Barberi, M., Colombo, S., Pedrazzini, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+of+a+tail-anchored+protein+to+endoplasmic+reticulum+and+mitochondrial+outer+membrane+by+independent+but+competing+pathways.">Targeting of a tail-anchored protein to endoplasmic reticulum and mitochondrial outer membrane by independent but competing pathways.</a> Mol. Biol. Cell. 12, 2482-2496 (2001).</li><li>Chudakov, D. M., Matz, M. V., Lukyanov, S., Lukyanov, K. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescent+proteins+and+their+applications+in+imaging+living+cells+and+tissues.">Fluorescent proteins and their applications in imaging living cells and tissues.</a> Physiol Rev. 90, 1103-1163 (2010).</li><li>Bancaud, A., Huet, S., Rabut, G., Ellenberg, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescence+perturbation+techniques+to+study+mobility+and+molecular+dynamics+of+proteins+in+live+cells+FRAP,+photoactivation,+photoconversion,+and+FLIP.">Fluorescence perturbation techniques to study mobility and molecular dynamics of proteins in live cells FRAP, photoactivation, photoconversion, and FLIP.</a> Cold Spring Harb. Protoc. 2010, (2010).</li><li>Michida, T., 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=Role+of+endothelin+1+in+hemorrhagic+shock-induced+gastric+mucosal+injury+in+rats.">Role of endothelin 1 in hemorrhagic shock-induced gastric mucosal injury in rats.</a> Gastroenterology. 106, 988-993 (1994).</li></ol>

The authors have nothing to disclose.

The protocols and imaging approaches described in this paper have been used to investigate the distribution and mobility of transfected TA fluorescent proteins resident in the ER of living cells. We have also analyzed the effect of the over-expression of these proteins on the architecture of this subcellular compartment by means of ultrastructural analyses.
The combination of live-cell confocal imaging and electron microscopy represents is a very powerful means of investigating the dynamic pro...

The discovery of green fluorescent protein (GFP) and its spectral variants, and the parallel development of fluorescence microscopy, have opened up completely new avenues for the investigation of protein behavior in cells. Techniques such as fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP), which are possible because of the intrinsic capacity of fluorophores to extinguish their fluorescence under intense illumination, are based on confocal live-cell imaging and the use of transfected fluorescent fusion proteins1-3. They are widely used to assess not only the localization of proteins, but also their mobility and vesicular transport, which can reveal important clues concerning their function4.
The unique feature of eukaryotic cells is the presence of intracellular compartments that have specific lipid and protein compositions. Although organelles are physically isolated, they need to communicate with each other and share molecular components in order to maintain cellular homeostasis. The secretory pathway guarantees that the proteins and lipids synthesized in the ER reach the correct final destination in which they exert their function. Intracellular organelles can also be connected by dynamic contact sites that allow molecules (lipids) to be directly exchanged between compartments. Moreover, many proteins have to assembled in large heteromeric complexes or associated with specific lipid species (lipid rafts/microdomains) in order to become functionally active or to be transported to their final destination. All of these biological aspects greatly influence the kinetic properties of proteins, and can therefore be appropriately investigated by means of the techniques described below.
Our group has widely used FRAP and FLIP combined with electron microscopy in order to study the architecture of the ER and its different subdomains. The ER is the first station of the secretory pathway and plays a key role in protein and lipid sorting5. It is a highly dynamic organelle whose distinct subdomains reflect its many different functions (i.e. protein and lipid biosynthesis and trafficking, protein folding, Ca2+ storage and release, and xenobiotic metabolism). However, although they are morphologically, spatially, and functionally distinct, these domains are continuous with each other, and their relative abundance can be modified in cells under physiological and pathological conditions. The best known and usually spatially segregated domains of the ER are the nuclear envelope, and the smooth and rough ER; however, we and others have demonstrated that there are ER structures with a more elaborate architecture and three-dimensional organization in various cell types and tissues under physiological conditions that can also be induced by means of stressful stimuli such as hypoxia, drug administration, or the over-expression of ER-resident transmembrane proteins2,6 (and references therein).
We have also recently demonstrated the presence of such structures in cell models of human diseases1,7. Originating from the stacked cisternae of smooth ER, they were given the collective name of organized smooth endoplasmic reticulum (OSER) in 20036, although they are also known as karmellae, lamellae, and crystalloid ER on the basis of their architecture which, like their size, can vary. After the cells are transfected with GFP fused to the cytosolic region of tail-anchored (TA) ER-resident proteins (dEGFP-ER), the weakly dimerizing tendency of GFP in trans dramatically alters the organization and structure of the ER. FRAP and FLIP experiments showed that dEGFP-ER is free to diffuse within OSERs, and the fact that it moves from the reticular ER to the OSER and vice versa indicates that the aggregates are continuous with the surrounding reticular ER. Ultrastructural analysis has allowed us to correlate the fluorescence data with a detailed description of OSER architecture and organization at nanoscale level: OSERs are always made up of stacks of paired cisternae of smooth ER but may have different forms of spatial organization, such as regularly arranged sinusoidal arrays or whorls, or hexagonal &#34;crystalloid&#34; tubular arrays. These rearrangements lead to cubic morphologies8 which, as they have been found in cells under physiological conditions9 and following stresses such as hypoxia10, drug treatment11, and cancer9, may have significant potential as ultrastructural markers.
After this first demonstration using GFP fusion proteins, we used imaging experiments to analyze the proliferation of ER domains in response to pharmacological treatments12, assess the tendency of fluorescent proteins to oligomerise in cells13, and to investigate the role of a mutant, ALS-linked TA protein in the formation of intracellular aggregates of ER origin that may be relevant to its pathogenicity1,8. It has been suggested that the formation of intracellular aggregates (which occurs in many neurodegenerative diseases14) may be a protective mechanism designed to prevent the interactions between toxic mutant proteins and the surrounding cell components15.
What follows is a description of a combination of optical and electron microscopy methods for investigating constructs whose C-terminal hydrophobic domains are inserted into the membrane of the ER, and an analysis of their dynamic behavior and the effects of their over-expression on ER domain architecture in cultured cells (see Figure 1 for a flowchart of the experimental protocol).

<table border="1">
		<tbody>
		 <tr>
			<td>Name of Material/ Equipment</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments/Description</td>
		 </tr>
		 <tr>
			<td>Dulbecco's Modified Eagle medium (DMEM)</td>
			<td>Invitrogen</td>
			<td>41966029</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Dulbecco's Modified Eagle medium (DMEM) w/o phenol red</td>
			<td>Invitrogen</td>
			<td>31053028</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Fetal Bovine Serum (FBS)</td>
			<td>Invitrogen</td>
			<td>10270106</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Pen/Strep</td>
			<td>Invitrogen</td>
			<td>15140-122</td>
			<td></td>
		 </tr>
		 <tr>
			<td>L-Glutamine 200 mM solution</td>
			<td>Invitrogen</td>
			<td>25030-024</td>
			<td></td>
		 </tr>
		 <tr>
			<td>jetPEI</td>
			<td>Polyplus Transfection</td>
			<td>PP10110</td>
			<td></td>
		 </tr>
		 <tr>
			<td>OxyFluor</td>
			<td>Oxyrase Inc.</td>
			<td>OF-0005</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Glutaraldehyde Grade I</td>
			<td>Sigma Aldrich</td>
			<td>G5882</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Sodium Cacodylate Trihydrate</td>
			<td>Sigma Aldrich</td>
			<td>C0250</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Osmium Tetroxide 4% solution</td>
			<td>Electron Microscopy Science</td>
			<td>19150</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Uranyl Acetate dihydrate</td>
			<td>Sigma Aldrich</td>
			<td>73943</td>
			<td>slightly radioactive</td>
		 </tr>
		 <tr>
			<td>Propylene Oxide</td>
			<td>Sigma-Aldrich</td>
			<td>82320</td>
			<td></td>
		 </tr>
		 <tr>
			<td>EPON embedding medium kit</td>
			<td>Sigma-Aldrich</td>
			<td>45359-1EA-F</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Lead Citrate </td>
			<td>Electron Microscopy Science</td>
			<td>17800</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Bench top centrifuge</td>
			<td>Eppendorf</td>
			<td>5415 D</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Spectral Confocal Microscope </td>
			<td>Leica Microsystems</td>
			<td>TCS SP5</td>
			<td></td>
		 </tr>
		 <tr>
			<td>CO2 Microscope Cage Incubation System </td>
			<td>OkoLab</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>Ultramicrotome </td>
			<td>Leica Microsystems</td>
			<td>UC6</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Diamond knife </td>
			<td>Diatome</td>
			<td>Ultra 45 &deg;</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Transmission Electron Microscope </td>
			<td>FEI</td>
			<td>Tecnai G2</td>
			<td></td>
		 </tr>
		 <tr>
			<td>GraphPad Prism Software</td>
			<td>GraphPad Software, Inc</td>
			<td></td>
			<td></td>
		 </tr>
		 <tr>
			<td>steel culture cell chamber for 24 mm coverslip</td>
			<td>Bioscience Tools</td>
			<td>CSC-25</td>
			<td></td>
		 </tr>
		 <tr>
			<td>Electron Microscopy grids</td>
			<td>Electron Microscopy Science</td>
			<td>G300Cu</td>
			<td></td>
		 </tr>
		</tbody>
 </table>

visualization of endoplasmic reticulum subdomains in cultured cells

The lipids and proteins in eukaryotic cells are continuously exchanged between cell compartments, although these retain their distinctive composition and functions despite the intense interorganelle molecular traffic. The techniques described in this paper are powerful means of studying protein and lipid mobility and trafficking in vivo and in their physiological environment. Fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) are widely used live-cell imaging techniques for studying intracellular trafficking through the exo-endocytic pathway, the continuity between organelles or subcompartments, the formation of protein complexes, and protein localization in lipid microdomains, all of which can be observed under physiological and pathological conditions. The limitations of these approaches are mainly due to the use of fluorescent fusion proteins, and their potential drawbacks include artifactual over-expression in cells and the possibility of differences in the folding and localization of tagged and native proteins. Finally, as the limit of resolution of optical microscopy (about 200 nm) does not allow investigation of the fine structure of the ER or the specific subcompartments that can originate in cells under stress (i.e. hypoxia, drug administration, the over-expression of transmembrane ER resident proteins) or under pathological conditions, we combine live-cell imaging of cultured transfected cells with ultrastructural analyses based on transmission electron microscopy.

Figure 2 shows an example FRAP study of protein mobility. The mobility of dEGFP-ER protein is demonstrated by the rapid fluorescence recovery after photobleaching in bleached OSERs. For the quantitative analysis, the half time and mobile fraction were derived from experimentally measured data by fitting the following monoexponential equation:
F(t) = Fpost + (Frec-Fpost)(1-e-t/&#964;)
wher...

Watch this Scientific Journal Video about Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells at JoVE.com

Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells

We describe the imaging approaches we use to investigate the distribution and mobility of the transfected fluorescent proteins resident in the endoplasmic reticulum (ER) by means of the confocal imaging of living cells. We also ultrastructurally analyze the effect of their expression on the architecture of this subcellular compartment.

The lipids and proteins in eukaryotic cells are continuously exchanged between cell compartments, although these retain their distinctive composition and ...

visualization-of-endoplasmic-reticulum-subdomains-in-cultured-cells

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12.9K Views.  Fondazione Filarete. We describe the imaging approaches we use to investigate the distribution and mobility of the transfected fluorescent proteins resident in the endoplasmic reticulum (ER) by means of the confocal imaging of living cells. We also ultrastructurally analyze the effect of their expression on the architecture of this subcellular compartment.

Video: Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells

Counting and Determining the Viability of Cultured Cells

Determining the number of cells in culture is important in standardization of culture conditions and in performing accurate quantitation experiments. A hemacytometer is a thick glass slide with a central area designed as a counting chamber. Cell suspension is applied to a defined area and counted so cell density can be calculated. 

Determining the number of cells in culture is important in standardization of culture conditions and in performing accurate quantitation experiments. In this video, we demonstrate how cells are counted using a hemacytometer.

Determining the number of cells in culture is important in standardization of culture conditions and in performing accurate quantitation experiments. A ...

Visualization of the Interstitial Cells of Cajal (ICC) Network in Mice

The interstitial cells of Cajal (ICC) are mesenchymal derived "pacemaker cells" of the gastrointestinal (GI) tract that generate spontaneous slow waves required for peristalsis and mediate neuronal input from the enteric nervous system1. Different subtypes of ICC form distinct networks in the muscularis of the GI tract 2,3. Loss or injury to these networks is associated with a number of motility disorders4. ICC cells express the KIT receptor tyrosine kinase on the plasma membrane and KIT immunostaining has been used for the past 15 years to label the ICC network5,6. Importantly, normal KIT activity is required for ICC development5,6. Neoplastic transformation of ICC cells results in gastrointestinal stromal tumor (GIST), that frequently harbor gain-of-function KIT mutations7,8. We recently showed that ETV1 is a lineage-specific survival factor expressed in the ICC/GIST lineage and is a master transcriptional regulator required for both normal ICC network formation and for of GIST tumorigenesis9. We further demonstrate that it cooperates with activating KIT mutations in tumorigenesis. Here, we describe methods for visualization of ICC networks in mice, largely based on previously published protocols10,11. More recently, the chloride channel anoctamin 1 (ANO1) has also been characterized as a specific membrane marker of ICC11,12. Because of their plasma membrane localization, immunofluorescence of both proteins can be used to visualize the ICC networks. Here, we describe visualization of the ICC networks by fixed-frozen cyrosections and whole mount preparations.

Visualization of the Interstitial Cells of Cajal ICC Network in Mice

The interstitial cells of Cajal (ICC) are the pacemaker cells of the gastrointestinal (GI) tract. They form complex networks between smooth muscle cells and post-ganglionic neuronal fibers to regulate GI contractility. Here, we present immunofluorescence methods cross-sectional and whole-mount visualization of murine ICC networks.

The interstitial cells of Cajal (ICC) are mesenchymal derived "pacemaker cells" of the gastrointestinal (GI) tract that generate spontaneous slow waves ...

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.

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 ...

Chromosome Preparation From Cultured Cells

Chromosome (cytogenetic) analysis is widely used for the detection of chromosome instability. When followed by G-banding and molecular techniques such as fluorescence in situ hybridization (FISH), this assay has the powerful ability to analyze individual cells for aberrations that involve gains or losses of portions of the genome&#160;and rearrangements involving one or more chromosomes. In humans, chromosome abnormalities occur in approximately 1 per 160 live births1,2, 60-80% of all miscarriages3,4, 10% of stillbirths2,5, 13% of individuals with congenital heart disease6, 3-6% of infertility cases2, and in many patients with developmental delay&#160;and birth defects7. Cytogenetic analysis of malignancy is routinely used by researchers and clinicians, as observations of clonal chromosomal abnormalities have been shown to have both diagnostic and prognostic significance8,9.&#160; Chromosome isolation is invaluable for gene therapy and stem cell research of organisms including nonhuman primates and rodents10-13.
Chromosomes can be isolated from cells of live tissues, including blood lymphocytes, skin fibroblasts, amniocytes, placenta, bone marrow, and tumor specimens. Chromosomes are analyzed at the metaphase stage of mitosis, when they are most condensed and therefore more clearly visible. The first step of the chromosome isolation technique involves the disruption of the spindle fibers by incubation with Colcemid, to prevent the cells from proceeding to the subsequent anaphase stage. The cells are then treated with a hypotonic solution and preserved in their swollen state with Carnoy&#39;s fixative. The cells are then dropped on to slides and can then be utilized for a variety of procedures. G-banding involves trypsin treatment followed by staining with Giemsa to create characteristic light and dark bands. The same procedure to isolate chromosomes can be used for the preparation of cells for procedures such as fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and spectral karyotyping (SKY)14,15.

Chromosomes can be isolated from live cells such as lymphocytes or skin fibroblasts, and from organisms including humans or mice. These chromosome preparations can be further utilized for routine G-banding and molecular cytogenetic procedures such as fluorescence in situ hybridization (FISH), comparative genomic hybridization (CGH), and spectral karyotyping (SKY).

Chromosome (cytogenetic) analysis is widely used for the detection of chromosome instability. When followed by G-banding and molecular techniques such as ...

Organelle Transport in Cultured Drosophila Cells: S2 Cell Line and Primary Neurons.

Drosophila S2 cells plated on a coverslip in the presence of any actin-depolymerizing drug form long unbranched processes filled with uniformly polarized microtubules. Organelles move along these processes by microtubule motors. Easy maintenance, high sensitivity to RNAi-mediated protein knock-down and efficient procedure for creating stable cell lines make Drosophila S2 cells an ideal model system to study cargo transport by live imaging. The results obtained with S2 cells can be further applied to a more physiologically relevant system: axonal transport in primary neurons cultured from dissociated Drosophila embryos. Cultured neurons grow long neurites filled with bundled microtubules, very similar to S2 processes. Like in S2 cells, organelles in cultured neurons can be visualized by either organelle-specific fluorescent dyes or by using fluorescent organelle markers encoded by DNA injected into early embryos or expressed in transgenic flies. Therefore, organelle transport can be easily recorded in neurons cultured on glass coverslips using living imaging. Here we describe procedures for culturing and visualizing cargo transport in Drosophila S2 cells and primary neurons. We believe that these protocols make both systems accessible for labs studying cargo transport.

Organelle Transport in Cultured Drosophila Cells: S2 Cell Line and Primary Neurons.

Drosophila S2 cells and cultured neurons are great systems for imaging of motor-driven organelle transport in vivo. Here we describe detailed protocols for culturing both cell types, their imaging and analysis of transport.

Drosophila S2 cells plated on a coverslip in the presence of any actin-depolymerizing drug form long unbranched processes filled with uniformly polarized ...

Visualization of G3BP Stress Granules Dynamics in Live Primary Cells

SGs can be visualized in cells by immunostaining of specific protein components or polyA+ mRNAs. SGs are highly dynamic and the study of their assembly and fate is important to understand the cellular response to stress. The deficiency in key factors of SGs like G3BP (RasGAP SH3 domain Binding Protein) leads to developmental defects in mice&#160;and alterations of the Central Nervous System. To study the dynamics of SGs in cells from an organism, one can culture primary cells and follow the localization of a transfected tagged component of SGs. We describe time-lapse experiment to observe G3BP1-containing SGs in Mouse Embryonic Fibroblasts (MEFs). This technique can also be used to study G3BP-containing SGs in live neurons, which is crucial as it was recently shown that these SGs are formed at the onset of neurodegenerative diseases like Alzheimer&#39;s disease. This approach can be adapted to any other cellular body and granule protein component, and performed with transgenic animals, allowing the live study of granules dynamics for example in the absence of a specific factor of these granules.

Stress granules (SGs) are cytoplasmic RNA granules containing stalled ribonucleoprotein particles (RNPs), and important in cellular response to various stresses. Dynamics of SGs can be followed in live cells by visualizing the localization of a tagged component of SGs in transfected primary cells after stress.

SGs can be visualized in cells by immunostaining of specific protein components or polyA+ mRNAs. SGs are highly dynamic and the study of their assembly ...

Massively Parallel Reporter Assays in Cultured Mammalian Cells

The genetic reporter assay is a well-established and powerful tool for dissecting the relationship between DNA sequences and their gene regulatory activities. The potential throughput of this assay has, however, been limited by the need to individually clone and assay the activity of each sequence on interest using protein fluorescence or enzymatic activity as a proxy for regulatory activity. Advances in high-throughput DNA synthesis and sequencing technologies have recently made it possible to overcome these limitations by multiplexing the construction and interrogation of large libraries of reporter constructs. This protocol describes implementation of a Massively Parallel Reporter Assay (MPRA) that allows direct comparison of hundreds of thousands of putative regulatory sequences in a single cell culture dish.

The genetic reporter assay is a well-established and powerful tool for dissecting the relationship between DNA sequences and their gene regulatory activities. Coupling candidate regulatory elements to reporter genes that carry identifying sequence tags enables massive parallelization of these assays.

The genetic reporter assay is a well-established and powerful tool for dissecting the relationship between DNA sequences and their gene regulatory ...

Imaging Local Ca2+ Signals in Cultured Mammalian Cells

Cytosolic Ca2+ ions regulate numerous aspects of cellular activity in almost all cell types, controlling processes as wide-ranging as gene transcription, electrical excitability and cell proliferation. The diversity and specificity of Ca2+ signaling derives from mechanisms by which Ca2+ signals are generated to act over different time and spatial scales, ranging from cell-wide oscillations and waves occurring over the periods of minutes to local transient Ca2+ microdomains (Ca2+ puffs) lasting milliseconds. Recent advances in electron multiplied CCD (EMCCD) cameras now allow for imaging of local Ca2+ signals with a 128 x 128 pixel spatial resolution at rates of &#62;500 frames sec-1 (fps). This approach is highly parallel and enables the simultaneous monitoring of hundreds of channels or puff sites in a single experiment. However, the vast amounts of data generated (ca. 1 Gb per min) render visual identification and analysis of local Ca2+ events impracticable. Here we describe and demonstrate the procedures for the acquisition, detection, and analysis of local IP3-mediated Ca2+ signals in intact mammalian cells loaded with Ca2+ indicators using both wide-field epi-fluorescence (WF) and total internal reflection fluorescence (TIRF) microscopy. Furthermore, we describe an algorithm developed within the open-source software environment Python that automates the identification and analysis of these local Ca2+ signals. The algorithm localizes sites of Ca2+ release with sub-pixel resolution; allows user review of data; and outputs time sequences of fluorescence ratio signals together with amplitude and kinetic data in an Excel-compatible table.

Imaging Local Ca2+ Signals in Cultured Mammalian Cells

Here we present techniques for imaging local IP3-mediated Ca2+ events using fluorescence microscopy in intact mammalian cells loaded with Ca2+ indicators together with an algorithm that automates identification and analysis of these events.

Cytosolic Ca2+ ions regulate numerous aspects of cellular activity in almost all cell types, controlling processes as wide-ranging as gene transcription, ...

Monitoring Endoplasmic Reticulum Calcium Homeostasis Using a Gaussia Luciferase SERCaMP

The endoplasmic reticulum (ER) contains the highest level of intracellular calcium, with concentrations approximately 5,000-fold greater than cytoplasmic levels. Tight control over ER calcium is imperative for protein folding, modification and trafficking. Perturbations to ER calcium can result in the activation of the unfolded protein response, a three-prong ER stress response mechanism, and contribute to pathogenesis in a variety of diseases. The ability to monitor ER calcium alterations during disease onset and progression is important in principle, yet challenging in practice. Currently available methods for monitoring ER calcium, such as calcium-dependent fluorescent dyes and proteins, have provided insight into ER calcium dynamics in cells, however these tools are not well suited for in vivo studies. Our lab has demonstrated that a modification to the carboxy-terminus of Gaussia luciferase confers secretion of the reporter in response to ER calcium depletion. The methods for using a luciferase based, secreted ER calcium monitoring protein (SERCaMP) for in vitro and in vivo applications are described herein. This video highlights hepatic injections, pharmacological manipulation of GLuc-SERCaMP, blood collection and processing, and assay parameters for longitudinal monitoring of ER calcium.

Monitoring Endoplasmic Reticulum Calcium Homeostasis Using a Gaussia Luciferase SERCaMP

Endoplasmic reticulum calcium homeostasis is disrupted in diverse pathologies. A secreted ER calcium monitoring protein (SERCaMP) reporter can be used to detect disruptions in the ER calcium store. This protocol describes the use of a Gaussia luciferase SERCaMP to examine ER calcium homeostasis in vitro and in vivo.

The endoplasmic reticulum (ER) contains the highest level of intracellular calcium, with concentrations approximately 5,000-fold greater than cytoplasmic ...

Measurement of Calcium Fluctuations Within the Sarcoplasmic Reticulum of Cultured Smooth Muscle Cells Using FRET-based Confocal Imaging

Maintenance of steady-state calcium (Ca2+) levels in the sarcoplasmic reticulum (SR) of vascular smooth muscle cells (VSMCs) is vital to their overall health. A significant portion of intracellular Ca2+ content is found within the SR stores in VSMCs. As the only intracellular organelle with a close association to the surrounding extracellular space through plasma membrane-SR junctions, the SR can be considered to constitute the first line of response to any irregularity in Ca2+ transients, or stress experienced by the cell. Among its many functions, one of the most important is its role in the transmission of Ca2+-regulated signals throughout the cell to induce further cell-wide reactions downstream. The more common use of cytoplasmic Ca2+ indicators in this regard is overall insufficient for research into the highly dynamic changes to the intraluminal SR Ca2+ store that have yet to be fully characterized. Here, we provide a detailed protocol for the direct and clear measurement of luminal SR Ca2+. This tool is useful for investigation into the nuanced changes in SR Ca2+ that have significant subsequent effects on the normal function and health of the cell. Fluctuations in SR Ca2+ content specifically can provide us with a significant amount of information pertaining to cellular responses to disease or stress conditions experienced by the cell. In this method, a modified version of a SR-targeted Ca2+ indicator, D1SR, is used to detect Ca2+ fluctuations in response to the introduction of agents to cultured rat aortic smooth muscle cells (SMCs). Following incubation with the D1SR indicator, confocal fluorescence microscopy and fluorescence resonance energy transfer (FRET)-based imaging are used to directly observe changes to intraluminal SR Ca2+ levels under control conditions and with the addition of agonist agents that function to induce intracellular Ca2+ movement.

Currently, most available calcium indicators are used to quantify cytoplasmic calcium transients as indirect measures of calcium released from the sarcoplasmic reticulum in cultured smooth muscle cells. This protocol describes the use of a specific FRET-based indicator that allows direct measurement of calcium signals within the sarcoplasmic reticulum lumen.

Maintenance of steady-state calcium (Ca2+) levels in the sarcoplasmic reticulum (SR) of vascular smooth muscle cells (VSMCs) is vital to their overall ...

Visualization of Endoplasmic Reticulum Subdomains in Cultured Cells

Summary

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Chapters in this video

Counting and Determining the Viability of Cultured Cells

Visualization of the Interstitial Cells of Cajal (ICC) Network in Mice

Visualization of Endoplasmic Reticulum Localized mRNAs in Mammalian Cells

Chromosome Preparation From Cultured Cells

Organelle Transport in Cultured Drosophila Cells: S2 Cell Line and Primary Neurons.

Visualization of G3BP Stress Granules Dynamics in Live Primary Cells

Massively Parallel Reporter Assays in Cultured Mammalian Cells

Imaging Local Ca²⁺ Signals in Cultured Mammalian Cells

Monitoring Endoplasmic Reticulum Calcium Homeostasis Using a Gaussia Luciferase SERCaMP

Measurement of Calcium Fluctuations Within the Sarcoplasmic Reticulum of Cultured Smooth Muscle Cells Using FRET-based Confocal Imaging