The authors dedicate this paper in honor of Prof. Gilberto Oliveira-Castro who introduced research in intercellular communication by gap junctions in Brazil. This work was funded by Capes, CNPQ and Faperj.

1. Preparation of Cells
<ol>
	<li>Maintain a culture of a thymic epithelial cell line (IT76M1) or cell to be tested in an incubator (37&#176;C/5% CO2).</li>
	<li>Wash the cells with PBS 1x (repeat this item 3x).</li>
	<li>Add Trypsin to the cells for 5 min.</li>
	<li>Add medium (twice of the volume of trypsin added in item 1.3) with 10% FBS (fetal bovine serum) to the cells with trypsin and centrifuge (800 x g for 5 min).</li>
	<li>Count the cells in a hemocytometer.</li>
	<li>Adjust the density of cells according to the cell type as the cells have to be in close contact with each other to allow coupling. Note: In our case, we used 3 x 105 cells per 35 mm Petri dish.</li>
</ol>
2. Micropipette Preparation
<ol>
	<li>Pull the micropipette as specified from a glass capillary micropipette (1.5 mm diameter) to a final 0.2 &#181;m of diameter so as to attain a final resistance of approximately 30 M&#937;17,18. 
	NOTE: Alternatively, injection pipettes can be purchased. The resistance depends on the cell size, for instance a higher resistance microelectrode would be necessary for pancreatic acinar cells, for example (100-150 M&#937;)19. A common problem that could occur is the precipitation of Lucifer Yellow solution which can then obstruct the micropipette and may require prior filtration or centrifugation. Before injection, the micropipette should be analyzed under the microscope to detect if there is an obstruction or any type of disruption13. The micropipette can be tested by injecting LY with the micropipette tip inside a saline solution.</li>
</ol>
3. Testing the Micropipette
<ol>
	<li>Prepare the Lucifer Yellow solution (5%) in 150 mmol/L LiCI and load the micropipette using a syringe or by backfilling (put into it LY Solution).</li>
	<li>Place the micropipette over the 35 mm Petri dish with the IT76M1 cells on the microinjection workstation and submerge the tip of the glass micropipette into the cell medium. Focus on the micropipette and perform a dye flowing test by applying a pulse.</li>
</ol>
4. Single-cell Lucifer Yellow Microinjection
<ol>
	<li>Focus the microscope right above the cell layer using a high magni&#64257;cation (40X), then slowly lower the pipette to the cells using the micromanipulator.</li>
	<li>Puncture the target cell when the tip is close enough to touch the cell membrane, and apply a small hyperpolarizing pulse to introduce the LY into the cell. The applied voltage will depend on the net charge of dye to be injected.&#160; Alternatively, some other dyes could be used with this technique as shown in Table 1. 
	Note: In principle any hydrophilic dye with MW less than 1KDa could be used. However, the rate of transfer could vary according to the weight and hydrophilicity. Additionally, unspecific transfer of the dye used must be evaluated.&#160;&#160;</li>
	<li>Capture cell images 3 min after dye injection or make a small movie with time lapse microscopy (30 fps). 
	NOTE: A similar approach could be seen in Hitomi et al (2015)20. To avoid communication by intercellular bridges (incomplete mitosis), a co-injection of rhodamin dextran (from 2 to 10 KDa), which does not pass through gap junctions but passes through intercellular bridges and certain types of nanotubules is recommended as shown in Figure 2.</li>
</ol>

<ol>
	<li>Bennett, M. V., 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=Gap+junctions:+new+tools,+new+answers,+new+questions.">Gap junctions: new tools, new answers, new questions.</a> Neuron. 6 (3), 305-320 (1991).</li><li>Orellana, J. A., Martinez, A. D., Retamal, 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=Gap+junction+channels+and+hemichannels+in+the+CNS:+Regulation+by+signaling+molecules.">Gap junction channels and hemichannels in the CNS: Regulation by signaling molecules.</a> Neuropharmacology. , (2013).</li><li>Peracchia, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+correlates+of+gap+junction+permeation.">Structural correlates of gap junction permeation.</a> Int Rev Cytol. 66, 81-146 (1980).</li><li>Loewenstein, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Junctional+intercellular+communication+and+the+control+of+growth.">Junctional intercellular communication and the control of growth.</a> Biochim Biophys Acta. 560 (1), 1-65 (1979).</li><li>Alves, L. A., 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=Functional+gap+junctions+in+thymic+epithelial+cells+are+formed+by+connexin+43.">Functional gap junctions in thymic epithelial cells are formed by connexin 43.</a> Eur.J Immunol. 25 (2), 431-437 (1995).</li><li>Alves, L. A., 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=Are+there+functional+gap+junctions+or+junctional+hemichannels+in+macrophages?.">Are there functional gap junctions or junctional hemichannels in macrophages?.</a> Blood. 88 (1), 328-334 (1996).</li><li>Fonseca, P. C., 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=Characterization+of+connexin+30.3+and+43+in+thymocytes.">Characterization of connexin 30.3 and 43 in thymocytes.</a> Immunology letters. 94 (1-2), 65-75 (2004).</li><li>Nihei, O. K., 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=Modulatory+effects+of+cAMP+and+PKC+activation+on+gap+junctional+intercellular+communication+among+thymic+epithelial+cells.">Modulatory effects of cAMP and PKC activation on gap junctional intercellular communication among thymic epithelial cells.</a> BMC Cell Biol. 11, 3 (2010).</li><li>Czyz, J., Szpak, K., Madeja, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+connexins+in+prostate+cancer+promotion+and+progression.">The role of connexins in prostate cancer promotion and progression.</a> Nat Rev Urol. 9 (5), 274-282 (2012).</li><li>El-Saghir, J. A., El-Habre, E. T., El-Sabban, M. E., Talhouk, R. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Connexins:+a+junctional+crossroad+to+breast+cancer.">Connexins: a junctional crossroad to breast cancer.</a> Int J Dev Biol. 55 (7-9), 773-780 (2011).</li><li>Cea, L. A., 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=Connexin-+and+pannexin-based+channels+in+normal+skeletal+muscles+and+their+possible+role+in+muscle+atrophy.">Connexin- and pannexin-based channels in normal skeletal muscles and their possible role in muscle atrophy.</a> J Membr Biol. 245 (8), 423-436 (2012).</li><li>Cotrina, M. L., Nedergaard, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Brain+connexins+in+demyelinating+diseases:+therapeutic+potential+of+glial+targets.">Brain connexins in demyelinating diseases: therapeutic potential of glial targets.</a> Brain Res. 1487, 61-68 (2012).</li><li>Park, H. a. n. -. A., R, S., Khanna, S. a. v. i. t. a., Sen, C. h. a. n. d. a. n. . K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+Technologies+in+Single-Cell+Microinjection+and+Application+to+Study+Signal+Transduction.">Current Technologies in Single-Cell Microinjection and Application to Study Signal Transduction.</a> Methods in Redox Signaling. , (2010).</li><li>Abbaci, M., Barberi-Heyob, M., Blondel, W., Guillemin, F., Didelon, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advantages+and+limitations+of+commonly+used+methods+to+assay+the+molecular+permeability+of+gap+junctional+intercellular+communication.">Advantages and limitations of commonly used methods to assay the molecular permeability of gap junctional intercellular communication.</a> Biotechniques. 45 (1), 33-52 (2008).</li><li>Stewart, W. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+connections+between+cells+as+revealed+by+dye-coupling+with+a+highly+fluorescent+naphthalimide+tracer.">Functional connections between cells as revealed by dye-coupling with a highly fluorescent naphthalimide tracer.</a> Cell. 14 (3), 741-759 (1978).</li><li>Meda, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Probing+the+function+of+connexin+channels+in+primary+tissues.">Probing the function of connexin channels in primary tissues.</a> Methods. 20 (2), 232-244 (2000).</li><li>Klaunig, J. E., Shi, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+gap+junctional+intercellular+communication.">Assessment of gap junctional intercellular communication.</a> Curr Protoc Toxicol. , (2009).</li><li>Hanani, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lucifer+yellow+-+an+angel+rather+than+the+devil.">Lucifer yellow - an angel rather than the devil.</a> J Cell Mol Med. 16 (1), 22-31 (2012).</li><li>Orci, L., Biochemistry, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blockage+of+Cell-to-Cell+Communication+within+Pancreatic+Acini+Is+Associated+with+Increased+Basal+Release+of+Amylase+Materials+and+Methods+Preparation+of+Acini.">Blockage of Cell-to-Cell Communication within Pancreatic Acini Is Associated with Increased Basal Release of Amylase Materials and Methods Preparation of Acini.</a> Cell. 103 (August), 475-483 (1986).</li><li>Hitomi, M., 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=Differential+connexin+function+enhances+self-renewal+in+glioblastoma.">Differential connexin function enhances self-renewal in glioblastoma.</a> Cell Rep. 11 (7), 1031-1042 (2015).</li><li>Nihei, O. K., Campos de Carvalho, ., C, A., Spray, D. C., Savino, W., Alves, L. 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+novel+form+of+cellular+communication+among+thymic+epithelial+cells:+intercellular+calcium+wave+propagation.">A novel form of cellular communication among thymic epithelial cells: intercellular calcium wave propagation.</a> Am J Physiol Cell Physiol. 285 (5), C1304-C1313 (2003).</li><li>Kanno, Y., Loewenstein, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intercellular+Diffusion.">Intercellular Diffusion.</a> Science. 143 (3609), 959-960 (1964).</li><li>Alves, L. A., Nihei, O. K., Fonseca, P. C., Carvalho, A. 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The authors have no conflicts of interest.

In order to verify the presence of functional intercellular gap junction, the use of tracers, which are membrane impermeable, although permeable by intercellular channels are required16. Fluorescein, the first fluorescent dye to observe cell-to-cell coupling22, is permeable between non junctional membranes3 and has therefore been substituted by Lucifer Yellow dye15. Currently, to find the best choice among the many different types of florescent tracers depends on the scope and conditions of the experiment. The procedure of cell loading with fluorescent dyes permits the evaluation of morphology, function of single cells and the kinetic rate of transfer between cells. Furthermore, dye microinjection allows a better understanding of the physiological role of gap junctions between cells21,23, since the degree of cellular communication is related with the number of coupled cells.
Several key factors are crucial for successfully obtaining microinjection data. Normal cell homeostasis and integrity must be maintained, thus a short injection time (&#60;1 s) of dye and technical expertise with microinjection is needed. Key factors in getting a better resolution of the captured images is having a cooled CCD camera, the fluorescence filters in place and the use of a high NA objective14. Also, some tips could be useful as: 1) cell culture dishes with grids are recommended to visualize a particular injected cell, also glass-bottom dishes should be used for high-resolution microscopy applications; 2) it is recommended to make 10-20 pulled needles before starting microinjections; 3) depending on the resistance of the electrode tip can be very helpful, loading the micropipette with the dye using capillarity by touching the pipette tip into the dye solution; 4) it is not necessary to load the whole body of the pipette, a few microliters to fill the tip and 2 to 3 mm above the tip is sufficient; 5) start the experiment with a less magnified lens and try to see the shadow of the pipette walls. Afterwards, move the pipette as close as possible and before touching the cell, shift to the higher magnification objective, such as 40x or greater; 6) Some groups use a pneumatic microinjector. Pneumatic injection is not the best choice since it is not precise and could inject unknown volumes; with a pulse the protocol could be standardized to inject a known volume of dye. Additionally, it is recommended to inject into the membrane above the cytosol because of the depth; injection in the membrane above the nucleus could injure it and affect cell physiology. Finally, cells that are not too flat are preferable over flat ones.
In summary, this method is effective to study intercellular communication by gap junctions but needs expertise/experience and good material and equipment to obtain high quality data. We hope that this article and video help beginners to understand and perform this technique.

Gap junctions are intercellular channels that allow the intercommunication among neighboring cells1. This communication connects two or more neighboring cells, where each one contributes with a connexon or hemichannel to form the intercellular channel. In mammalian cells, the connexon is formed by six connexins, monomers with four transmembrane domains and a C and N terminal within the cytoplasm2. Gap junctions not only permit the flow of ions, second messengers and small metabolites, but also contribute to many forms of cellular communication in many physiological processes, such as synaptic transmission, heart contraction, cell growth and differentiation3,4,5,6,7,8. In addition gap junctions have been associated with many diseases including cancer9,10, muscular atrophy11, some genetic diseases and demyelinating diseases12.
This type of intercellular crosstalk can be evaluated by several methods13,14,15,16. In this paper, we show how to perform a single-cell microinjection of Lucifer Yellow to visualize cellular communication via gap-junctions in living cells. We discuss how to prepare the cells and the micropipette, the usage of the micromanipulator and the injection of Lucifer Yellow dye in a thymic epithelial cell line. Usually, this experimental procedure could be analyzed by the average of connected cells to the cell loaded with dye. In addition, this method could be used with other fluorescent dyes with molecular weight below the gap junctions cut-off which is approximately 1,000 daltons.

<table><tbody><tr><td>Lucifer yellow</td><td>Sigma</td><td>L0259</td><td></td></tr><tr><td>Lithium Chloride</td><td>Sigma</td><td>L4408</td><td></td></tr><tr><td>PBS tablets</td><td>Sigma&amp;nbsp;</td><td>P4417</td><td></td></tr><tr><td>RPMI</td><td>Sigma</td><td>R4130</td><td></td></tr><tr><td>Bovine fetal serum</td><td>Cultilab</td><td></td><td></td></tr><tr><td>Trypsin</td><td>Sigma</td><td>T4799</td><td></td></tr><tr><td>vibration-insulated table&amp;nbsp;</td><td>Newport</td><td>VH3036W-OPT</td><td>A vibration-insulated table is needed to protect the experiments from vibration and avoid cell damage</td></tr><tr><td>Micromanipulator</td><td>Narishige</td><td>MMO-203</td><td>This equipment allows precision adjustments of the micropipette, which is needed for cell micro injection.</td></tr><tr><td>Current Generator&amp;nbsp;</td><td>Digitimer</td><td>DS2</td><td>To produce the dye flow through the micropipette, a current below one nano ampere was given using a current generator with an electrode inside the micropipette or an amplifier which has a capacitance compensation circuit (old electrometer) or current injection functions of new patch clamp amplifiers, and the ground wire submersed in the plate dish. Alternatively, the dye can be injected by a pneumatic microinjector, following the factory recommendations.&amp;nbsp;&amp;nbsp;&amp;nbsp;</td></tr></tbody></table>

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.

Thymic epithelial cell line IT-76MI were used to evaluate dye coupling by gap junctions as these cells were described to express functional gap junctions formed by connexin 4321. Figure 1 shows the injection of Lucifer Yellow when applied in the one cell below the tip of the pipette. After few minutes, connected cells become fluorescent (asterisks) indicating the diffusion of the fluorescent dye through the gap junctions. The number of cells and time to became fluorescent is directly associated with the degree of cellular communication among these cells. Figure 2 shows the injection of LY in thymic epithelial cells and the inserts (insert d) show the co-injection of LY and Rhodamine Dextran (10KDa). As expected the LY passes to a neighboring cell, although the Rhodamine Dextran does not because of its high molecular weight. In addition, the presence of a GJ blocker (insert f), octanol, blocked the passage of the dye to the surrounding cells. Alternatively, one can evaluate the degree of coupling of a specific cell or the effect of a drug on the function of GJ. Figure 3A shows the injection of LY in TEC cells with or without dexamethasone. Then 100 cells were injected, in the presence of dexamethasone and the percentage of 1 or 2 cells communicating was similar in relation to the control without the drug. However the number of 3 or 4 cells communicating was higher when compared to control. Five or 6 cells and 7 or 8 cells with GJ communication in the presence of dexamethasone was not observed in the control, thus indicating that dexamethasone increased the degree of coupling in TEC cells.
<img alt="Figure 1" src="/files/ftp_upload/50836/50836fig1.jpg" /> 
Figure 1: Lucifer Yellow injection in IT-76MI cells. (A) The micropipette close to the cell membrane. (B) The pipette is seen by fluorescence microscopy. (C) A test pulse was generated to verify whether the electrode is actually injecting the dye. (D) The pipette touched the cell membrane and it was charged with Lucifer Yellow dye. (E) The cell charged allowed the dye to pass through gap junctions to at least five neighbor cells (indicated by the arrows), X20. F) A digital zoom was done to allow better visualization. Asterisks point out the cells that were charged in the contrast phase microscopy (Figure 1A). <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/50836/50836fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/50836/50836fig2.jpg" /> 
Figure 2: Lucifer Yellow injection in thymic epithelial cells (TEC). Phase contrast and fluorescence microscopy. (A and B) Human Thymic Epithelial cell. (C and D) Thymic Nurse Cell, (E and F) A Mouse Thymic Epithelial cell line, respectively. The insert in (D) shows the same cell (arrow) after an injection of rhodamine-dextran 10KDa (not permeable through gap junctions). The inserts in (E) and (F) show the absence of dye transfer in the TEC line pre-treated with octanol 1 mM (a gap junction blocker) for 10 min. In all panels asterisks mark the injected cells. (A-F) X 200. Reproduced from Alves et al., 19955. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/50836/50836fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/50836/50836fig3.jpg" /> 
Figure 3: Gap junction communication increased by dexamethasone in a rat epithelial cell line. TEC were treated with 1 &#181;M dexamethasone, and coupling degree was evaluated by the Lucifer Yellow dye transfer assay. (A) Microscopy fields (phase contrast and fluorescence, respectively, in the left and right panels) depicting the injected cell and those that were coupled when LY was injected (magnification 320X). In all panels asterisks mark the injected cells. (B) Histograms showing the pattern of coupling of control and dexamethasone-treated cells. The analysis comprises of 100 microinjections per group. Reproduced from Alves et al., 200023. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/50836/50836fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>DYE</td>
			<td>MW</td>
			<td>Excitation/Emission</td>
		</tr>
		<tr>
			<td>hydroxycoumarin carboxylic acid</td>
			<td>206</td>
			<td>386/488</td>
		</tr>
		<tr>
			<td>calcein blue</td>
			<td>321</td>
			<td>360/449</td>
		</tr>
		<tr>
			<td>4&#8242;,6-diamidino-2-phenylindole dihydrochloride</td>
			<td>279</td>
			<td>358/461</td>
		</tr>
		<tr>
			<td>carboxyfluorescein</td>
			<td>376</td>
			<td>492/517</td>
		</tr>
		<tr>
			<td>ethidium iodide(bromide)</td>
			<td>314</td>
			<td>518/605</td>
		</tr>
		<tr>
			<td>Lucifer Yellow CH</td>
			<td>443</td>
			<td>428/536</td>
		</tr>
		<tr>
			<td>alexa fluor 488</td>
			<td>570.5</td>
			<td>495/519</td>
		</tr>
		<tr>
			<td>calcein</td>
			<td>622</td>
			<td>494/517</td>
		</tr>
		<tr>
			<td>propidium iodide</td>
			<td>414</td>
			<td>535/617</td>
		</tr>
	</tbody>
</table>
Table 1: Dyes currently used for microinjection experiments. Here in, some used dyes with molecular weight and the excitation/emission wavelength.

Watch this Scientific Journal Video about Single-cell Microinjection for Cell Communication Analysis at JoVE.com

Single-cell Microinjection for Cell Communication Analysis

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 ...

single-cell-microinjection-for-cell-communication-analysis

Universidad San Sebastian

Research

JoVE Journal

Biology

11.2K Views.  Oswaldo Cruz Foundation. 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.

Video: Single-cell Microinjection for Cell Communication Analysis

Transcriptome Analysis of Single Cells

Many gene expression analysis techniques rely on material isolated from heterogeneous populations of cells from tissue homogenates or cells in culture.1,2,3 In the case of the brain, regions such as the hippocampus contain a complex arrangement of different cell types, each with distinct mRNA profiles. The ability to harvest single cells allows for a more in depth investigation into the molecular differences between and within cell populations. We describe a simple and rapid method for harvesting cells for further processing. Pipettes often used in electrophysiology are utilized to isolate (using aspiration) a cell of interest and conveniently deposit it into an Eppendorf tube for further processing with any number of molecular biology techniques. Our protocol can be modified for the harvest of dendrites from cell culture or even individual cells from acute slices.
We also describe the aRNA amplification method as a major downstream application of single cell isolations. This method was developed previously by our lab as an alternative to other gene expression analysis techniques such as reverse-transcription or real-time polymerase chain reaction (PCR).4,5,6,7,8 This technique provides for linear amplification of the polyadenylated RNA beginning with only femtograms of material and resulting in microgram amounts of antisense RNA. The linearly amplified material provides a more accurate estimation than PCR exponential amplification of the relative abundance of components of the transcriptome of the isolated cell. The basic procedure consists of two rounds of amplification. Briefly, a T7 RNA polymerase promoter site is incorporated into double stranded cDNA created from the mRNA transcripts. An overnight in vitro transcription (IVT) reaction is then performed in which T7 RNA polymerase produces many antisense transcripts from the double stranded cDNA. The second round repeats this process but with some technical differences since the starting material is antisense RNA. It is standard to repeat the second round, resulting in three rounds of amplification. Often, the third round in vitro transcription reaction is performed using biotinylated nucleoside triphosphates so that the antisense RNA produced can be hybridized and detected on a microarray.7,8

In this article we describe a simple method for the harvesting of single cells from rat primary neuronal cultures and subsequent transcriptome analysis using aRNA amplification. This approach is generalizable to any cell type.

Many gene expression analysis techniques rely on material isolated from heterogeneous populations of cells from tissue homogenates or cells in ...

Neuroscience

A Microfluidic Chip for the Versatile Chemical Analysis of Single Cells

We present a microfluidic device that enables the quantitative determination of intracellular biomolecules in multiple single cells in parallel. For this purpose, the cells are passively trapped in the middle of a microchamber. Upon activation of the control layer, the cell is isolated from the surrounding volume in a small chamber. The surrounding volume can then be exchanged without affecting the isolated cell. However, upon short opening and closing of the chamber, the solution in the chamber can be replaced within a few hundred milliseconds. Due to the reversibility of the chambers, the cells can be exposed to different solutions sequentially in a highly controllable fashion, e.g. for incubation, washing, and finally, cell lysis. The tightly sealed microchambers enable the retention of the lysate, minimize and control the dilution after cell lysis. Since lysis and analysis occur at the same location, high sensitivity is retained because no further dilution or loss of the analytes occurs during transport. The microchamber design therefore enables the reliable and reproducible analysis of very small copy numbers of intracellular molecules (attomoles, zeptomoles) released from individual cells. Furthermore, many microchambers can be arranged in an array format, allowing the analysis of many cells at once, given that suitable optical instruments are used for monitoring. We have already used the platform for proof-of-concept studies to analyze intracellular proteins, enzymes, cofactors and second messengers in either relative or absolute quantifiable manner.

In this article we present a microfluidic chip for single cell analysis. It allows the quantification of intracellular proteins, enzymes, cofactors, and second messengers by means of fluorescent assays or immunoassays.&#160;

We present a microfluidic device that enables the quantitative determination of intracellular biomolecules in multiple single cells in parallel. For this ...

Bioengineering

Intranuclear Microinjection of DNA into Dissociated Adult Mammalian Neurons

Primary neuronal cell cultures are valuable tools to study protein function since they represent a more biologically relevant system compared to immortalized cell lines. However, the post-mitotic nature of primary neurons prevents effective heterologous protein expression using common procedures such as electroporation or chemically-mediated transfection. Thus, other techniques must be employed in order to effectively express proteins in these non-dividing cells.
In this article, we describe the steps required to perform intranuclear injections of cDNA constructs into dissociated adult sympathetic neurons. This technique, which has been applied to different types of neurons, can successfully induce heterologous protein expression. The equipment essential for the microinjection procedure includes an inverted microscope to visualize cells, a glass injection pipet filled with cDNA solution that is connected to a N2(g) pressure delivery system, and a micromanipulator. The micromanipulator coordinates the injection motion of microinjection pipet with a brief pulse of pressurized N2 to eject cDNA solution from the pipet tip. 
This technique does not have the toxicity associated with many other transfection methods and enables multiple DNA constructs to be expressed at a consistent ratio. The low number of injected cells makes the microinjection procedure well suited for single cell studies such as electrophysiological recordings and optical imaging, but may not be ideal for biochemical assays that require a larger number of cells and higher transfection efficiencies. Although intranuclear microinjections require an investment of equipment and time, the ability to achieve high levels of heterologous protein expression in a physiologically relevant environment makes this technique a very useful tool to investigate protein function.

Direct intranuclear injection of cDNA is an effective transfection technique for post-mitotic cells. This method provides high levels of heterologous protein expression from single or multiple cDNA constructs and enables protein function to be studied in a physiologically relevant environment with a variety of single cell assays.

Primary neuronal cell cultures are valuable tools to study protein function since they represent a more biologically relevant system compared to ...

Analysis of mRNA Nuclear Export Kinetics in Mammalian Cells by Microinjection

In eukaryotes, messenger RNA (mRNA) is transcribed in the nucleus and must be exported into the cytoplasm to access the translation machinery. Although the nuclear export of mRNA has been studied extensively in Xenopus oocytes1 and genetically tractable organisms such as yeast2 and the Drosophila derived S2 cell line3, few studies had been conducted in mammalian cells. Furthermore the kinetics of mRNA export in mammalian somatic cells could only be inferred indirectly4,5. In order to measure the nuclear export kinetics of mRNA in mammalian tissue culture cells, we have developed an assay that employs the power of microinjection coupled with fluorescent in situ hybridization (FISH). These assays have been used to demonstrate that in mammalian cells, the majority of mRNAs are exported in a splicing dependent manner6,7, or in manner that requires specific RNA sequences such as the signal sequence coding region (SSCR) 6. In this assay, cells are microinjected with either in vitro synthesized mRNA or plasmid DNA containing the gene of interest. The microinjected cells are incubated for various time points then fixed and the sub-cellular localization of RNA is assessed using FISH. In contrast to transfection, where transcription occurs several hours after the addition of nucleic acids, microinjection of DNA or mRNA allows for rapid expression and allows for the generation of precise kinetic data.

Here we describe an assay that employs the power of microinjection coupled with fluorescent in situ hybridization in order to accurately measure the nuclear export kinetics of mRNA in mammalian somatic cells.

In eukaryotes, messenger RNA (mRNA) is transcribed in the nucleus and must be exported into the cytoplasm to access the translation machinery. Although ...

Correlative Light and Electron Microscopy (CLEM) as a Tool to Visualize Microinjected Molecules and their Eukaryotic Sub-cellular Targets

The eukaryotic cell relies on complex, highly regulated, and functionally distinct membrane bound compartments that preserve a biochemical polarity necessary for proper cellular function. Understanding how the enzymes, proteins, and cytoskeletal components govern and maintain this biochemical segregation is therefore of paramount importance. The use of fluorescently tagged molecules to localize to and/or perturb subcellular compartments has yielded a wealth of knowledge and advanced our understanding of cellular regulation. Imaging techniques such as fluorescent and confocal microscopy make ascertaining the position of a fluorescently tagged small molecule relatively straightforward, however the resolution of very small structures is limited 1.
On the other hand, electron microscopy has revealed details of subcellular morphology at very high resolution, but its static nature makes it difficult to measure highly dynamic processes with precision 2,3. Thus, the combination of light microscopy with electron microscopy of the same sample, termed Correlative Light and Electron Microscopy (CLEM) 4,5, affords the dual advantages of ultrafast fluorescent imaging with the high-resolution of electron microscopy 6. This powerful technique has been implemented to study many aspects of cell biology 5,7. Since its inception, this procedure has increased our ability to distinguish subcellular architectures and morphologies at high resolution. 
Here, we present a streamlined method for performing rapid microinjection followed by CLEM (Fig. 1). The microinjection CLEM procedure can be used to introduce specific quantities of small molecules and/or proteins directly into the eukaryotic cell cytoplasm and study the effects from millimeter to multi-nanometer resolution (Fig. 2). The technique is based on microinjecting cells grown on laser etched glass gridded coverslips affixed to the bottom of live cell dishes and imaging with both confocal fluorescent and electron microscopy. Localization of the cell(s) of interest is facilitated by the grid pattern, which is easily transferred, along with the cells of interest, to the Epon resin used for immobilization of samples and sectioning prior to electron microscopy analysis (Fig. 3). Overlay of fluorescent and EM images allows the user to determine the subcellular localization as well as any morphological and/or ultrastructural changes induced by the microinjected molecule of interest (Fig. 4). This technique is amenable to time points ranging from &le;5 s up to several hours, depending on the nature of the microinjected sample.

Correlative Light and Electron Microscopy CLEM as a Tool to Visualize Microinjected Molecules and their Eukaryotic Sub-cellular Targets

The CLEM technique has been adapted to analyze ultrastructural morphology of membranes, organelles, and subcellular structures affected by microinjected molecules. This method combines the powerful techniques of micromanipulation/microinjection, confocal fluorescent microscopy, and electron microscopy to allow millimeter to multi-nanometer resolution. This technique is amenable to a wide variety of applications.


The eukaryotic cell relies on complex, highly regulated, and functionally distinct membrane bound compartments that preserve a biochemical polarity ...

Manipulation of Single Neural Stem Cells and Neurons in Brain Slices using Robotic Microinjection

A central question in developmental neurobiology is how neural stem and progenitor cells form the brain. To answer this question, one needs to label, manipulate, and follow single cells in the brain tissue with high resolution over time. This task is extremely challenging due to the complexity of tissues in the brain. We have recently developed a robot, that guide a microinjection needle into brain tissue upon utilizing images acquired from a microscope to deliver femtoliter volumes of solution into single cells. The robotic operation increases resulting an overall yield that is an order of magnitude greater than manual microinjection and allows for precise labeling and flexible manipulation of single cells in living tissue. With this, one can microinject hundreds of cells within a single organotypic slice. This article demonstrates the use of the microinjection robot for automated microinjection of neural progenitor cells and neurons in the brain tissue slices. More broadly, it can be used on any epithelial tissue featuring a surface that can be reached by the pipette. Once set up, the microinjection robot can execute 15 or more microinjections per minute. The microinjection robot because of its throughput and versality will make microinjection a broadly straightforward high-performance cell manipulation technique to be used in bioengineering, biotechnology, and biophysics for performing single-cell analyses in organotypic brain slices.

This protocol demonstrates the use of a robotic platform for microinjection into single neural stem cells and neurons in brain slices. This technique is versatile and offers a method of tracking cells in tissue with high spatial resolution.

A central question in developmental neurobiology is how neural stem and progenitor cells form the brain. To answer this question, one needs to label, ...

Analysis of Spliceosomal snRNA Localization in Human Hela Cells Using Microinjection

Biogenesis of spliceosomal snRNAs is a complex process involving both nuclear and cytoplasmic phases and the last step occurs in a nuclear compartment called the Cajal body. However, sequences that direct snRNA localization into this subnuclear structure have not been known until recently. To determine sequences important for accumulation of snRNAs in Cajal bodies, we employed microinjection of fluorescently labelled snRNAs followed by their localization inside cells. First, we prepared snRNA deletion mutants, synthesized DNA templates for in vitro transcription and transcribed snRNAs in the presence of UTP coupled with Alexa488. Labelled snRNAs were mixed with 70 kDa-Dextran conjugated with TRITC, and microinjected to the nucleus or the cytoplasm of human HeLa cells. Cells were incubated for 1 h and fixed and the Cajal body marker coilin was visualized by indirect immunofluorescence, while snRNAs and dextran, which serves as a marker of nuclear or cytoplasmic injection, were observed directly using a fluorescence microscope. This method allows for efficient and rapid testing of how various sequences influence RNA localization inside cells. Here, we show the importance of the Sm-binding sequence for efficient localization of snRNAs into the Cajal body.

Biogenesis of spliceosomal snRNAs is a complex process involving various cellular compartments. Here, we employed microinjection of fluorescently labelled snRNAs in order to monitor their transport inside the cell.

Biogenesis of spliceosomal snRNAs is a complex process involving both nuclear and cytoplasmic phases and the last step occurs in a nuclear compartment ...

High Throughput Microinjections of Sea Urchin Zygotes

Microinjection into cells and embryos is a common technique that is used to study a wide range of biological processes. In this method a small amount of treatment solution is loaded into a microinjection needle that is used to physically inject individual immobilized cells or embryos. Despite the need for initial training to perform this procedure for high-throughput delivery, microinjection offers maximum efficiency and reproducible delivery of a wide variety of treatment solutions (including complex mixtures of samples) into cells, eggs or embryos. Applications to microinjections include delivery of DNA constructs, mRNAs, recombinant proteins, gain of function, and loss of function reagents. Fluorescent or colorimetric dye is added to the injected solution to enable instant visualization of efficient delivery as well as a tool for reliable normalization of the amount of the delivered solution. The described method enables microinjection of 100-400 sea urchin zygotes within 10-15 min.

Microinjection is a common technique used to deliver DNA constructs, mRNAs, morpholino antisense oligonucleotides or other treatments into eggs, embryos, and cells of various species.

Microinjection into cells and embryos is a common technique that is used to study a wide range of biological processes. In this method a small amount of ...

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 ...

Microinjection of Drosophila Nurse Cells: A Method of Intracellular Delivery

Source: Catrina, I. E., et al. <a href="https://www-jove-com.bdigitaluss.remotexs.co/video/58545/" target="_blank">Visualizing and Tracking Endogenous mRNAs in Live Drosophila melanogaster Egg Chambers</a>. J. Vis. Exp. (2019).
Due to their large size and relatively simple organization, Drosophila nurse cells are ideally suited for live cell imaging studies. This video describes a microinjection method for exogenous compounds delivery into the cells, and the featured protocol demonstrates the procedure with fluorescent oligonucleotide probes called molecular beacons (MBs) used to visualize endogenous mRNA transcripts.

Mikroiniekcja komórek pielęgniarskich Drosophila: metoda dostarczania wewnątrzkomórkowego

Source: Catrina, I. E., et al. Visualizing and Tracking Endogenous mRNAs in Live Drosophila melanogaster Egg Chambers. J. Vis. Exp. (2019).
Due to their ...