We would like to thank the Worcester Polytechnic Institute Department of Chemistry and Biochemistry for funding.

1. Transfection of Cell Lines
Transfection Method 1
(Lonza Nucleofection for increased primary cell transfection efficiency)
<ol>
	<li>Cells should be of recent passage and in log phase growth prior to transfection. Wash cells in phophate buffered saline (PBS) and harvest cells by trypsinization.</li>
	<li>Collect cells by centrifugation at 1500 x g for 5 minutes.</li>
	<li>Add sterilized cover slips to a 6-well plate. Cover slips may be coated for enhanced cell adhesion. Place 1.5 mL of culture media (in this case Dulbecco's modified Eagle's medium (DMEM), 10% fetal bovine serum (FBS)) into each well and equilibrate the media in the incubator.</li>
	<li>Harvest the cells by trypsinization and resuspend in a minimal volume of phosphate buffered saline (PBS).</li>
	<li>Count the cells and centrifuge the correct amount of resuspension to provide ~5x10 5 cells per sample.</li>
	<li>Resuspend the cells carefully in 100 &mu;L room temperature Nucleofector solution per sample.</li>
	<li>Combine 100 &mu;L of cell suspension with 5 &mu;g plasmid DNA and transfer the sample to a Nucleofector Cuvette being careful not to include air bubbles.</li>
	<li>Select the appropriate Nucleofector Program (this may require previous testing to establish optimal transfection efficiency with minimal mortality).</li>
	<li>Insert the cuvette containing the cell/DNA suspension into the Nucleofector Cuvette Holder and begin the selected program.</li>
	<li>Upon completion, remove the cuvette and add ~500 &mu;L of pre-equilibrated culture media to it (taken from the 6-well plate).</li>
	<li>Immediately transfer the sample into the 6-well plate with final volume of 1.5 mL per well. Cells should be plated in either mixed populations or separately, for controls.</li>
</ol>
Transfection Method 2
(Qiagen Effectene transfection for cell lines)
<ol>
	<li>Prepare transfection complexes using the Qiagen Effectene Reagent by first adding 0.8 &mu;g of each plasmid DNA sample to 200 &mu;L EC buffer.</li>
	<li>Add 6.4 &mu;L enhancer reagent to each sample, mix briefly by flicking the tube, and incubate for 2 minutes at room temperature.</li>
	<li>Add 20 &mu;L Effectene reagent to each sample, mix by flicking the tube, and incubate for 15 minutes at room temperature.</li>
	<li>During this incubation, prepare the two cell lines of interest for transfection. Wash recently passaged cells (&lt;80% confluence) once in phosphate buffered saline (PBS). Add back 1.5 mL fresh warmed and equilibrated growth medium (in this case Dulbecco's modified Eagle's medium (DMEM), 10% fetal bovine serum (FBS)).</li>
	<li>Once the transfection complexes have incubated for 15 minutes, transfer 1.2 mL of media to each sample. Mix by pipetting, and immediately transfer ~700 &mu;L of the complexes to each of two wells in the 6-well plate. Add dropwise, and mix by gently by swirling the plate. Allow cells to transfect for at least 3 hours (may vary with cell type).</li>
	<li>Add sterilized cover slips to a new 6-well plate. Cover slips may be coated for enhanced cell adhesion.</li>
	<li>After the cells have transfected, wash cells twice with PBS and harvest the cells by minimal trysinization by adding approximately 100 &mu;L trypsin solution to each well, briefly agitating the plate to fully coat each well, and immediately aspirating off the trypsin. Once the cells have lifted, add 1.5 mL fresh media.</li>
	<li>At this point, cells should be plated in either mixed or separate populations (for controls) onto the sterile cover slips.</li>
	<li>Allow cells to recover for 12 hours.</li>
</ol>
2. Cell Fusion
<ol>
	<li>Remove culture media from the cells and wash twice with PBS.</li>
	<li>At this point, it is recommended to treat the cells with cycloheximide (100 &mu;g/mL) to inhibit protein synthesis. Allow the cells to incubate for 2 hours and then wash the cells twice with PBS.</li>
	<li>Fuse cells by exposing them to a solution of 50% polyethylene glycol 1000 (PEG 1000) in serum- free DMEM for 125 seconds at room temperature.</li>
	<li>Wash cells with PBS to remove the PEG 1000 solution, and add 2 mL freshly warmed and equilibrated media.</li>
	<li>Allow cells to incubate for 18 - 24 hours.</li>
</ol>
Fluorescence Microscopy
<ol>
	<li>Remove the culture media, and wash the cells twice in PBS.</li>
	<li>Fix cells by adding 1 mL of a 4% paraformaldehyde solution (in PBS) to each well. Gently agitate for 15 minutes.</li>
	<li>Wash the fixed cells twice in PBS.</li>
	<li>Carefully remove the cover slips from the plate, wick off excess PBS. Invert onto microscope slides loaded with one drop of mounting medium (90% glycerol, 100mM Tris pH 7.5, 2% DABCO (1,4-diazabicoyclo-octane) containing DAPI (4',6-diamidino-2-phenylindole).</li>
	<li>Remove excess mounting medium from the slides, and seal cover slips with nail polish.</li>
	<li>Visualize the cells via confocal or epifluorescence microscopy.</li>
</ol>
3. Representative Results
Figure 2 shows an example heterokaryon experiment using primary fibroblasts and H1299 non-small cell lung carcinoma cells. The protein of interest in this experiment (Chicken Anemia Virus-VP3) displays primarily cytoplasmic localization in primary cell types and nuclear localization in transformed cell types as visualized by epifluorescence microscopy. The protein is expressed as a fusion to either GFP (pEGFP-N1 vector, Clontech) in primary foreskin fibroblasts (PFF) or dsRed (dsRed-N1 vector, Clontech) in H1299 cells. Control samples involving self-fusions (top two rows) display multinucleated cells with no change in steady-state localization patterns. Such changes could otherwise occur due to sensitivity to fusion conditions or the formation of syncitia. Heterokaryon fusions (bottom row) demonstrate nuclear entry of the GFP-fused primary cell-derived protein and colocalization with the dsRed-fused protein in response to the introduction of transformed cell material. The example shown is a relatively rare heterokaryon fusion resulting from only two cells, one of each type, as demonstrated by the presence of both fluoroprotein signals. In addition to detecting these types of localization transitions, nucleocytoplasmic shuttling activity can be easily detected by the presence of a single fluorophore in both nuclei. This type of determination is clear when examining 1:1 cell fusions and would depend on inhibition of translation.
<img src="/files/ftp_upload/2488/2488fig1.jpg" alt="Figure 1" /> Figure 1. Flow chart of the heterokaryon method using primary fibroblasts and H1299 non-small cell carcinoma cells. The gene of interest is cloned to produce an in-frame fusion to one of two fluorescent protein genes. Cell lines are then transiently transfected with either construct and allowed to recover. Heterokaryon formation is induced by brief treatment with polyethylene glycol (PEG) followed by further incubation. Finally, the sub-cellular localization of the protein of interest is observed using various forms of fluorescent microscopy.
<img src="/files/ftp_upload/2488/2488fig2.jpg" alt="Figure 2" /> Figure 2. Nucleocytoplasmic trafficking and shuttling activity of the Chicken Anemia Virus VP3 protein visualized by heterokaryon fusion. Top row: Representative images of self-fused H1299 cells expressing dsRed-VP3. Middle row: Representative epifluorescence images of primary foreskin fibroblast cells (PFF) expressing GFP-VP3 after PEG fusion. Bottom row: Heterokaryon fusion of PFF and H1299 cells. Yellow indicates colocalization of GFP and dsRed signals. Cells were imaged using a Leica AF6000E fluorescence microscope and Leica imaging software.

<ol>
	<li>Belaya, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FLIPing+heterokaryons+to+analyze+nucleo-cytoplasmic+shuttling+of+yeast+proteins.">FLIPing heterokaryons to analyze nucleo-cytoplasmic shuttling of yeast proteins.</a> RNA. 12, 921-930 (2006).</li><li>Bhaumik, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+target+of+a+transcriptional+activator+revealed+by+fluorescence+resonance+energy+transfer.">In vivo target of a transcriptional activator revealed by fluorescence resonance energy transfer.</a> Genes Dev. 18, 333-343 (2004).</li><li>Cohen, H. R., Panning, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=XIST+RNA+exhibits+nuclear+retention+and+exhibits+reduced+association+with+the+export+factor+TAP/NXF1.">XIST RNA exhibits nuclear retention and exhibits reduced association with the export factor TAP/NXF1.</a> Chromosoma. 116, 373-383 (2007).</li><li>Gao, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dapper1+is+a+nucleoplasmic+shuttling+protein+that+negatively+modulates+Wnt+signaling+in+the+nucleus.">Dapper1 is a nucleoplasmic shuttling protein that negatively modulates Wnt signaling in the nucleus.</a> J. Biol. Chem. 51, 35679-3588 (2008).</li><li>Grespin, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thyroid+Hormone+Receptor+&#945;1+Follows+a+Cooperative+CRM1/Calreticulin-mediated+Nuclear+Export+Pathway.">Thyroid Hormone Receptor &#945;1 Follows a Cooperative CRM1/Calreticulin-mediated Nuclear Export Pathway.</a> J. Biol. Chem. 283, 25576-25588 (2008).</li><li>Heilman, D. W., Teodoro, J. G., Green, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptin+Nucleocytoplasmic+Shuttling+Is+Required+for+Cell+Type-Specific+Localization,+Apoptosis,+and+Recruitment+of+the+Anaphase-Promoting+Complex/Cyclosome+to+PML+Bodies.">Apoptin Nucleocytoplasmic Shuttling Is Required for Cell Type-Specific Localization, Apoptosis, and Recruitment of the Anaphase-Promoting Complex/Cyclosome to PML Bodies.</a> J. Virology. 80, 7535-7545 (2006).</li><li>Jeffries, S., Capobianco, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neoplastic+transformation+by+Notch+requires+nuclear+localization.">Neoplastic transformation by Notch requires nuclear localization.</a> Mol Cell Biol. 20, 3928-3941 (2000).</li><li>Keaton, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleocytoplasmic+trafficking+of+G2/M+regulators+in+yeast.">Nucleocytoplasmic trafficking of G2/M regulators in yeast.</a> Mol. Biol. Cell. 19, 4006-4018 (2008).</li><li>Ling, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear-Cytoplasmic+Shuttling+Is+Not+Required+for+the+Epstein-Barr+Virus+EBNA-LP+Transcriptional+Coactivation+Function.">Nuclear-Cytoplasmic Shuttling Is Not Required for the Epstein-Barr Virus EBNA-LP Transcriptional Coactivation Function.</a> J. Virology. 83, 7109-7116 (2009).</li><li>Lin, X. -. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=RXR&#945;+acts+as+a+carrier+for+TR3+nuclear+export+in+a+9-cis+retinoic+acid-dependent+manner+in+gastric+cancer+cells.">RXR&#945; acts as a carrier for TR3 nuclear export in a 9-cis retinoic acid-dependent manner in gastric cancer cells.</a> J. Cell Science. 117, 5609-5621 (2004).</li><li>Vissinga, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nuclear+Export+of+NBN+Is+Required+for+Normal+Cellular+Responses+to+Radiation.">Nuclear Export of NBN Is Required for Normal Cellular Responses to Radiation.</a> Mol Cell Biol. 29, 1000-1006 (2009).</li><li>Zimmerman, R. S., Rosenberg, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changes+in+p19Arf+localization+accompany+apoptotic+crisis+during+pre-B-cell+transformation+by+Abelson+murine+leukemia+virus.">Changes in p19Arf localization accompany apoptotic crisis during pre-B-cell transformation by Abelson murine leukemia virus.</a> J. Virol. 82, 8383-8391 (2008).</li></ol>

No conflicts of interest declared.

The heterokaryon protocol presented here provides an efficient and easily interpretable method for the characterization of cell type-specific localization behavior as well as nucleocytoplasmic shuttling activity. This method takes advantage of the sensitivity of fluorescence analysis as well as the ability to image live cells and perform studies of protein dynamics. The technique is easily adapted for many different cell types and is amenable to both live and fixed cell imaging. For example, inverted fluorescence microscopy can be used for live imaging and time lapse video capture. By contrast, mounted cells may be used in either epifluorescence microscopy for determination of steady-state localizations or more detailed confocal imaging of discrete localizations. Moreover, techniques such as fluorescence recovery after photobleaching (FRAP), or fluorescence loss in photobleaching (FLIP) can be used in the determination of localization kinetics1. The incorporation of alternate fluorophores in the protocol would allow for protein interaction experiments such as fluorescence resonance energy transfer (FRET) to be conducted in concert2. Various inhibitors of cellular trafficking such as leptomycin B or dominant negative Ran GTPase constructs can be used to establish dependence on particular import or export pathways5,6,9.
<ul>
	<li>In certain experiments involving shuttling activity, care must be taken to avoid localization effects due to synthesis of new protein. In these cases, translation inhibitors or limited time points must be used. However, artifacts due to translational inhibition remain a possibility. Cell fusions containing one of each cell type are most desired for clear interpretation of shuttling and localization behavior. Optimization of cell number and fusion conditions (timing and concentration) may be necessary to promote such favorable 1:1 fusion events.</li>
	<li>It is important to note that optimization of certain steps in the protocol will be necessary depending on the particular cell types used. Aspects in the experimental procedure such as fusion efficiency, transfection efficiency, and viability after fusion may vary greatly between cell types. In particular, primary cell types can be challenging to manage due to complex culture conditions and low transfection efficiencies. Use of technologies such as the Lonza Nucleofector device can allow for rapid processing of cells as well as dramatically increased transfection efficiencies. Additionally, electroporation methods allow for easy transfer of cells in suspension to the fusion steps that follow.</li>
</ul>

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		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
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<tr>
<td>Effectene reagent</td>
<td>&nbsp;</td>
<td>Qiagen</td>
<td>301425</td>
<td>&nbsp;</td>
<tr>
<td>Phosphate buffered saline (PBS)</td>
<td>&nbsp;</td>
<td>Sigma-Aldrich</td>
<td>P5493</td>
<td>&nbsp;</td>
<tr>
<td>Trypsin</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>SH3023602</td>
<td>&nbsp;</td>
<tr>
<td>Dulbecco&#x2019;s modified Eagle&#x2019;s medium (DMEM)</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>SH30243FS</td>
<td>High glucose</td>
</tr>
<tr>
<td>paraformaldehyde</td>
<td>&nbsp;</td>
<td>FisherChemical</td>
<td>O4042-500</td>
<td>&nbsp;</td>
<tr>
<td>4&#x2019;,6-diamidino-2-phenylindole (DAPI)</td>
<td>&nbsp;</td>
<td>Sigma-Aldrich</td>
<td>D9542-10MG</td>
<td>&nbsp;</td>
<tr>
<td>Hyclone Serum (fetal bovine)</td>
<td>&nbsp;</td>
<td>Thermo Scientific</td>
<td>SH3008803HI</td>
<td>&nbsp;</td>
<tr>
<td>Falcon 6-well plates</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>08-772-1B</td>
<td>&nbsp;</td>
<tr>
<td>Polyethylene glycol 1000</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>528875-25GM</td>
<td>&nbsp;</td>
<tr>
<td>Cover slips</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>12-545-85</td>
<td>&nbsp;</td>
<tr>
<td>DABCO</td>
<td>&nbsp;</td>
<td>Sigma-Aldrich</td>
<td>D2522-25G</td>
<td>&nbsp;</td>
<tr>
<td>Nucleofector HDF kit</td>
<td>&nbsp;</td>
<td>Lonza</td>
<td>VPD-1001</td>
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heterokaryon technique for analysis of cell type-specific localization

A significant number of proteins are regulated by subcellular trafficking or nucleocytolasmic shuttling. These proteins display a diverse array of cellular functions including nuclear import/export of RNA and protein, transcriptional regulation, and apoptosis. Interestingly, major cellular reorganizations including cell division, differentiation and transformation, often involve such activities3,4,8,10. The detailed study of these proteins and their respective regulatory mechanisms can be challenging as the stimulation for these localization changes can be elusive, and the movements themselves can be quite dynamic and difficult to track. Studies involving cellular oncogenesis, for example, continue to benefit from understanding pathways and protein activities that differ between normal primary cells and transformed cells6,7,11,12. As many proteins show altered localization during transformation or as a result of transformation, methods to efficiently characterize these proteins and the pathways in which they participate stand to improve the understanding of oncogenesis and open new areas for drug targeting.
Here we present a method for the analysis of protein trafficking and shuttling activity between primary and transformed mammalian cells. This method combines the generation of heterokaryon fusions with fluorescence microscopy to provide a flexible protocol that can be used to detect steady-state or dynamic protein localizations. As shown in Figure 1, two separate cell types are transiently transfected with plasmid constructs bearing a fluoroprotein gene attached to the gene of interest. After expression, the cells are fused using polyethylene glycol, and protein localizations may then be imaged using a variety of methods. The protocol presented here is a fundamental approach to which specialized techniques may be added.

Watch this Scientific Journal Video about Heterokaryon Technique for Analysis of Cell Type-specific Localization at JoVE.com

Heterokaryon Technique for Analysis of Cell Type-specific Localization

A flexible and efficient method for the characterization of cell type-specific protein localization and nucleocytoplasmic shuttling is described. This heterokaryon approach uses fluorescently-labeled fusion proteins to image protein localizations after cell fusion. The protocol is amenable to steady-state localizations or more dynamic determinations based on live cell imaging.

A significant number of proteins are regulated by subcellular trafficking or nucleocytolasmic shuttling.  These proteins display a diverse array of ...

heterokaryon-technique-for-analysis-of-cell-type-specific-localization

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Biology

16.3K Views.  Worcester Polytechnic Institute- WPI. A flexible and efficient method for the characterization of cell type-specific protein localization and nucleocytoplasmic shuttling is described. This heterokaryon approach uses fluorescently-labeled fusion proteins to image protein localizations after cell fusion. The protocol is amenable to steady-state localizations or more dynamic determinations based on live cell imaging.

Video: Heterokaryon Technique for Analysis of Cell Type-specific Localization

A Neuronal and Astrocyte Co-Culture Assay for High Content Analysis of Neurotoxicity

High Content Analysis (HCA) assays combine cells and detection reagents with automated imaging and powerful image analysis algorithms, allowing measurement of multiple cellular phenotypes within a single assay. In this study, we utilized HCA to develop a novel assay for neurotoxicity. Neurotoxicity assessment represents an important part of drug safety evaluation, as well as being a significant focus of environmental protection efforts. Additionally, neurotoxicity is also a well-accepted in vitro marker of the development of neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Recently, the application of HCA to neuronal screening has been reported. By labeling neuronal cells with &beta;III-tubulin, HCA assays can provide high-throughput, non-subjective, quantitative measurements of parameters such as neuronal number, neurite count and neurite length, all of which can indicate neurotoxic effects. However, the role of astrocytes remains unexplored in these models. Astrocytes have an integral role in the maintenance of central nervous system (CNS) homeostasis, and are associated with both neuroprotection and neurodegradation when they are activated in response to toxic substances or disease states. GFAP is an intermediate filament protein expressed predominantly in the astrocytes of the CNS. Astrocytic activation (gliosis) leads to the upregulation of GFAP, commonly accompanied by astrocyte proliferation and hypertrophy. This process of reactive gliosis has been proposed as an early marker of damage to the nervous system. The traditional method for GFAP quantitation is by immunoassay. This approach is limited by an inability to provide information on cellular localization, morphology and cell number. We determined that HCA could be used to overcome these limitations and to simultaneously measure multiple features associated with gliosis - changes in GFAP expression, astrocyte hypertrophy, and astrocyte proliferation - within a single assay. In co-culture studies, astrocytes have been shown to protect neurons against several types of toxic insult and to critically influence neuronal survival. Recent studies have suggested that the use of astrocytes in an in vitro neurotoxicity test system may prove more relevant to human CNS structure and function than neuronal cells alone. Accordingly, we have developed an HCA assay for co-culture of neurons and astrocytes, comprised of protocols and validated, target-specific detection reagents for profiling &beta;III-tubulin and glial fibrillary acidic protein (GFAP). This assay enables simultaneous analysis of neurotoxicity, neurite outgrowth, gliosis, neuronal and astrocytic morphology and neuronal and astrocytic development in a wide variety of cellular models, representing a novel, non-subjective, high-throughput assay for neurotoxicity assessment. The assay holds great potential for enhanced detection of neurotoxicity and improved productivity in neuroscience research and drug discovery.

This article describes a novel protocol and reagent set designed for sensitive measurement of neurotoxic effects of compounds and treatments on co-cultures of neurons and astrocytes using high content analysis. Results demonstrate that high content analysis represents an exciting novel technology for neurotoxicity assessment.

High Content Analysis (HCA) assays combine cells and detection reagents with automated imaging and powerful image analysis algorithms, allowing ...

Visualizing RNA Localization in Xenopus Oocytes

RNA localization is a conserved mechanism of establishing cell polarity. Vg1 mRNA localizes to the vegetal pole of Xenopus laevis oocytes and acts to spatially restrict gene expression of Vg1 protein. Tight control of Vg1 distribution in this manner is required for proper germ layer specification in the developing embryo. RNA sequence elements in the 3' UTR of the mRNA, the Vg1 localization element (VLE) are required and sufficient to direct transport. To study the recognition and transport of Vg1 mRNA in vivo, we have developed an imaging technique that allows extensive analysis of trans-factor directed transport mechanisms via a simple visual readout. 
To visualize RNA localization, we synthesize fluorescently labeled VLE RNA and microinject this transcript into individual oocytes. After oocyte culture to allow transport of the injected RNA, oocytes are fixed and dehydrated prior to imaging by confocal microscopy. Visualization of mRNA localization patterns provides a readout for monitoring the complete pathway of RNA transport and for identifying roles in directing RNA transport for cis-acting elements within the transcript and trans-acting factors that bind to the VLE (Lewis et al., 2008, Messitt et al., 2008). We have extended this technique through co-localization with additional RNAs and proteins (Gagnon and Mowry, 2009, Messitt et al., 2008), and in combination with disruption of motor proteins and the cytoskeleton (Messitt et al., 2008) to probe mechanisms underlying mRNA localization.

Visualizing RNA Localization in Xenopus Oocytes

Visualization of in vivo RNA transport is accomplished by microinjection of fluorescently labeled RNA transcripts into Xenopus oocytes, followed by confocal microscopy.

RNA localization is a conserved mechanism of establishing cell polarity.  Vg1 mRNA localizes to the vegetal pole of Xenopus laevis oocytes and acts to ...

Investigating Tissue- and Organ-specific Phytochrome Responses using FACS-assisted Cell-type Specific Expression Profiling in Arabidopsis thaliana

Light mediates an array of developmental and adaptive processes throughout the life cycle of a plant. Plants utilize light-absorbing molecules called photoreceptors to sense and adapt to light. The red/far-red light-absorbing phytochrome photoreceptors have been studied extensively. Phytochromes exist as a family of proteins with distinct and overlapping functions in all higher plant systems in which they have been studied1. Phytochrome-mediated light responses, which range from seed germination through flowering and senescence, are often localized to specific plant tissues or organs2. Despite the discovery and elucidation of individual and redundant phytochrome functions through mutational analyses, conclusive reports on distinct sites of photoperception and the molecular mechanisms of localized pools of phytochromes that mediate spatial-specific phytochrome responses are limited. We designed experiments based on the hypotheses that specific sites of phytochrome photoperception regulate tissue- and organ-specific aspects of photomorphogenesis, and that localized phytochrome pools engage distinct subsets of downstream target genes in cell-to-cell signaling. We developed a biochemical approach to selectively reduce functional phytochromes in an organ- or tissue-specific manner within transgenic plants. Our studies are based on a bipartite enhancer-trap approach that results in transactivation of the expression of a gene under control of the Upstream Activation Sequence (UAS) element by the transcriptional activator GAL43. The biliverdin reductase (BVR) gene under the control of the UAS is silently maintained in the absence of GAL4 transactivation in the UAS-BVR parent4. Genetic crosses between a UAS-BVR transgenic line and a GAL4-GFP enhancer trap line result in specific expression of the BVR gene in cells marked by GFP expression4. BVR accumulation in Arabidopsis plants results in phytochrome chromophore deficiency in planta5-7. Thus, transgenic plants that we have produced exhibit GAL4-dependent activation of the BVR gene, resulting in the biochemical inactivation of phytochrome, as well as GAL4-dependent GFP expression. Photobiological and molecular genetic analyses of BVR transgenic lines are yielding insight into tissue- and organ-specific phytochrome-mediated responses that have been associated with corresponding sites of photoperception4, 7, 8. Fluorescence Activated Cell Sorting (FACS) of GFP-positive, enhancer-trap-induced BVR-expressing plant protoplasts coupled with cell-type-specific gene expression profiling through microarray analysis is being used to identify putative downstream target genes involved in mediating spatial-specific phytochrome responses. This research is expanding our understanding of sites of light perception, the mechanisms through which various tissues or organs cooperate in light-regulated plant growth and development, and advancing the molecular dissection of complex phytochrome-mediated cell-to-cell signaling cascades.

Investigating Tissue- and Organ-specific Phytochrome Responses using FACS-assisted Cell-type Specific Expression Profiling in Arabidopsis thaliana

The molecular basis of spatial-specific phytochrome responses is being investigated using transgenic plants that exhibit tissue- and organ-specific phytochrome deficiencies. The isolation of specific cells exhibiting induced phytochrome chromophore depletion by Fluorescence-Activated Cell Sorting followed by microarray analyses is being utilized to identify genes involved in spatial-specific phytochrome responses.

Light mediates an array of developmental and adaptive processes throughout the life cycle of a plant. Plants utilize light-absorbing molecules called ...

Single-cell Microinjection for Cell Communication Analysis

Gap junctions are intercellular channels that allow the communication of neighboring cells. This communication depends on the contribution of a hemichannel by each neighboring cell to form the gap junction. In mammalian cells, the hemichannel is formed by six connexins, monomers with four transmembrane domains and a C and N terminal within the cytoplasm. Gap junctions permit the exchange of ions, second messengers, and small metabolites. In addition, they have important roles in many forms of cellular communication within physiological processes such as synaptic transmission, heart contraction, cell growth and differentiation. We detail how to perform a single-cell microinjection of Lucifer Yellow to visualize cellular communication via gap-junctions in living cells. It is expected that in functional gap junctions, the dye will diffuse from the loaded cell to the connected cells. It is a very useful technique to study gap junctions since you can evaluate the diffusion of the fluorescence in real time. We discuss how to prepare the cells and the micropipette, how to use a micromanipulator and inject a low molecular weight fluorescent dye in an epithelial cell line.

We describe here how to perform a single-cell microinjection of Lucifer Yellow to visualize cellular communication via gap-junctions in living cells, and provide some useful tips. We expect that this paper will help everyone to evaluate the degree of cellular coupling due to functional gap junctions. Everything described here could be, in principle, adapted to other fluorescent dyes with molecular weight below 1,000 Daltons.

Gap junctions are intercellular channels that allow the communication of neighboring cells. This communication depends on the contribution of a ...

Micromanipulation Techniques Allowing Analysis of Morphogenetic Dynamics and Turnover of Cytoskeletal Regulators

Examining the spatiotemporal dynamics of proteins can reveal their functional importance in various contexts. In this article, it is discussed how fluorescent recovery after photobleaching (FRAP) and photoactivation techniques can be used to study the spatiotemporal dynamics of proteins in subcellular locations. We also show how these techniques enable straightforward determination of various parameters linked to actin cytoskeletal regulation and cell motility. Moreover, the microinjection of cells is additionally described as an alternative treatment (potentially preceding or complementing the aforementioned photomanipulation techniques) to trigger instantaneous effects of translocated proteins on cell morphology and function. Micromanipulation such as protein injection or local application of plasma membrane-permeable drugs or cytoskeletal inhibitors can serve as powerful tool to record immediate consequences of a given treatment on cell behavior at the single cell and subcellular level. This is exemplified here by immediate induction of lamellipodial cell edge protrusion by the injection of recombinant Rac1 protein, as established a quarter-century ago. In addition, we provide a protocol for determining the turnover of enhanced green fluorescent protein (EGFP)-VASP, an actin filament polymerase prominently accumulating at lamellipodial tips of B16-F1 cells, employing FRAP and including associated data analysis and curve fitting. We also present guidelines for estimating the rates of lamellipodial actin network polymerization, as exemplified by cells expressing EGFP-tagged &#946;-actin. Finally, instructions are given for how to investigate the rates of actin monomer mobility within the cell cytoplasm, followed by actin incorporation at sites of rapid filament assembly, such as the tips of protruding lamellipodia, using photoactivation approaches. None of these protocols is&#160;restricted to components or regulators of the actin cytoskeleton, but can easily be extended to explore in analogous fashion the spatiotemporal dynamics and function of proteins in various different subcellular structures or functional contexts.

We describe how micro- and photomanipulation techniques such as FRAP and photoactivation enable the determination of motility parameters and the spatiotemporal dynamics of proteins within migrating cells. Experimental readouts include subcellular dynamics and turnover of motility regulators or of the underlying actin cytoskeleton.

Examining the spatiotemporal dynamics of proteins can reveal their functional importance in various contexts. In this article, it is discussed how ...

TChIP-Seq: Cell-Type-Specific Epigenome Profiling

Epigenetic regulation plays central roles in gene expression. Since histone modification was discovered in the 1960s, its physiological and pathological functions have been extensively studied. Indeed, the advent of next-generation deep sequencing and chromatin immunoprecipitation (ChIP) via specific histone modification antibodies has revolutionized our view of epigenetic regulation across the genome. Conversely, tissues typically consist of diverse cell types, and their complex mixture poses analytic challenges to investigating the epigenome in a particular cell type. To address the cell type-specific chromatin state in a genome-wide manner, we recently developed tandem chromatin immunoprecipitation sequencing (tChIP-Seq), which is based on the selective purification of chromatin by tagged core histone proteins from cell types of interest, followed by ChIP-Seq. The goal of this protocol is the introduction of best practices of tChIP-Seq. This technique provides a versatile tool for tissue-specific epigenome investigation in diverse histone modifications and model organisms.

We describe a step-by-step protocol for tandem chromatin immunoprecipitation sequencing (tChIP-Seq) that enables the analysis of cell-type-specific genome-wide histone modification.

Epigenetic regulation plays central roles in gene expression. Since histone modification was discovered in the 1960s, its physiological and pathological ...

Assessment of Zebrafish Lens Nucleus Localization and Sutural Integrity

The zebrafish is uniquely suited to genetic manipulation and in vivo imaging, making it an increasingly popular model for reverse genetic studies and for generation of transgenics for in vivo imaging. These unique capabilities make the zebrafish an ideal platform to study ocular lens development and physiology. Our recent findings that an Aquaporin-0, Aqp0a, is required for stability of the anterior lens suture, as well as for the shift of the lens nucleus to the lens center with age led us to develop tools especially suited to analyzing the properties of zebrafish lenses. Here we outline detailed methods for lens dissection that can be applied to both larval and adult lenses, to prepare them for histological analysis, immunohistochemistry and imaging. We focus on analysis of lens suture integrity and cortical cell morphology and compare data generated from dissected lenses with data obtained from in vivo imaging of lens morphology made possible by a novel transgenic zebrafish line with a genetically encoded fluorescent marker. Analysis of dissected lenses perpendicular to their optical axis allows quantification of the relative position of the lens nucleus along the anterior-posterior axis. Movement of the lens nucleus from an initial anterior position to the center is required for normal lens optics in adult zebrafish. Thus, a quantitative measure of lens nuclear position directly correlates with its optical properties.

These protocols were developed to analyze cortical lens morphology, structural integrity of the zebrafish lens sutures in fixed and live lenses and to measure the position of the zebrafish lens nucleus along the anterior-posterior axis.

The zebrafish is uniquely suited to genetic manipulation and in vivo imaging, making it an increasingly popular model for reverse genetic studies and for ...

Cell Type-specific Gene Expression Profiling in the Mouse Liver

Liver repopulation after injury is a crucial feature of mammals which prevents immediate organ failure and death after exposure of environmental toxins. A deeper understanding of the changes in gene expression that occur during repopulation could help identify therapeutic targets to promote the restoration of liver function in the setting of injuries. Nonetheless, methods to isolate specifically the repopulating hepatocytes are inhibited by a lack of cell markers, limited cell numbers, and the fragility of these cells. The development of translating ribosome affinity purification (TRAP) technology in conjunction with the Fah-/- mouse model to recapitulate repopulation in the setting of liver injury allows gene expression profiling of the repopulating hepatocytes. With TRAP, cell type-specific translating mRNA is rapidly and efficiently isolated. We developed a method that utilizes TRAP with affinity-based isolation of translating mRNA from hepatocytes that selectively express the green fluorescent protein (GFP)-tagged ribosomal protein (RP), GFP:RPL10A. TRAP circumvents the long time period required for fluorescence-activated cell sorting that could change the gene expression profile. Furthermore, since only the repopulating hepatocytes express the GFP:RPL10A fusion protein, the isolated mRNA is devoid of contamination from the surrounding injured hepatocytes and other cell types in the liver. The affinity-purified mRNA is of high quality and allows downstream PCR- or high-throughput sequencing-based analysis of gene expression.

Translating ribosome affinity purification (TRAP) enables rapid and efficient isolation of cell type-specific translating mRNA. Here, we demonstrate a method that combines hydrodynamic tail-vein injection in a mouse model of liver repopulation and TRAP to examine the expression profile of repopulating hepatocytes.

Liver repopulation after injury is a crucial feature of mammals which prevents immediate organ failure and death after exposure of environmental toxins. A ...

The CryoAPEX Method for Electron Microscopy Analysis of Membrane Protein Localization Within Ultrastructurally-Preserved Cells

Key cellular events like signal transduction and membrane trafficking rely on proper protein location within cellular compartments. Understanding precise subcellular localization of proteins is thus important for answering many biological questions. The quest for a robust label to identify protein localization combined with adequate cellular preservation and staining has been historically challenging. Recent advances in electron microscopy (EM) imaging have led to the development of many methods and strategies to increase cellular preservation and label target proteins. A relatively new peroxidase-based genetic tag, APEX2, is a promising leader in cloneable EM-active tags. Sample preparation for transmission electron microscopy (TEM) has also advanced in recent years with the advent of cryofixation by high pressure freezing (HPF) and low-temperature dehydration and staining via freeze substitution (FS). HPF and FS provide excellent preservation of cellular ultrastructure for TEM imaging, second only to direct cryo-imaging of vitreous samples. Here we present a protocol for the cryoAPEX method, which combines the use of the APEX2 tag with HPF and FS. In this protocol, a protein of interest is tagged with APEX2, followed by chemical fixation and the peroxidase reaction. In place of traditional staining and alcohol dehydration at room temperature, the sample is cryofixed and undergoes dehydration and staining at low temperature via FS. Using cryoAPEX, not only can a protein of interest be identified within subcellular compartments, but also additional information can be resolved with respect to its topology within a structurally preserved membrane. We show that this method can provide high enough resolution to decipher protein distribution patterns within an organelle lumen, and to distinguish the compartmentalization of a protein within one organelle in close proximity to other unlabeled organelles. Further, cryoAPEX is procedurally straightforward and amenable to cells grown in tissue culture. It is no more technically challenging than typical cryofixation and freeze substitution methods. CryoAPEX is widely applicable for TEM analysis of any membrane protein that can be genetically tagged.

This protocol describes the cryoAPEX method, in which an APEX2-tagged membrane protein can be localized by transmission electron microscopy within optimally-preserved cell ultrastructure.

Key cellular events like signal transduction and membrane trafficking rely on proper protein location within cellular compartments. Understanding precise ...

Analyzing the &alpha;-Actinin Network in Human iPSC-Derived Cardiomyocytes Using Single Molecule Localization Microscopy

The maturation of iPSC-derived cardiomyocytes is a critical issue for their application in regenerative therapy, drug testing and disease modeling. Despite the development of multiple differentiation protocols, the generation of iPSC cardiomyocytes resembling an adult-like phenotype remains challenging. One major aspect of cardiomyocytes maturation involves the formation of a well-organized sarcomere network to ensure high contraction capacity. Here, we present a super resolution-based approach for semi-quantitative analysis of the &#945;-actinin network in cardiomyocytes. Using photoactivated localization microscopy a comparison of sarcomere length and z-disc thickness of iPSC-derived cardiomyocytes and cardiac cells isolated from neonatal tissue was performed. At the same time, we demonstrate the importance of proper imaging conditions to obtain reliable data. Our results show that this method is suitable to quantitatively monitor the structural maturity of cardiac cells with high spatial resolution, enabling the detection of even subtle changes of sarcomere organization.

Analyzing the &amp;#945;-Actinin Network in Human iPSC-Derived Cardiomyocytes Using Single Molecule Localization Microscopy

The formation of a proper sarcomere network is important for the maturation of iPSC-derived cardiomyocytes. We present a super resolution-based approach that allows for the quantitative evaluation of the structural maturation of stem cell derived cardiomyocytes, to improve culture conditions promoting cardiac development.

The maturation of iPSC-derived cardiomyocytes is a critical issue for their application in regenerative therapy, drug testing and disease modeling. ...