This work was supported by the Federal Ministry of Education and Research Germany (FKZ 0312138A and FKZ 316159), the State Mecklenburg-Western Pomerania with EU Structural Funds (ESF/IVWM-B34-0030/10 and ESF/IVBM-B35-0010/12), the DFG (DA1296-1), and the German Heart Foundation (F/01/12). In addition, R.D. is supported by the FORUN Program of Rostock University Medical Centre (889001), the DAMP Foundation, and the BMBF (VIP+ 00240).

All steps in this protocol involving neonatal mice were performed per the ethical guidelines for animal care of the Rostock University Medical Centre.
1. Preparation of Cell Culture Dishes and the Medium for Cardiomyocyte Culture
<ol>
	<li>Coat a cell culture plate with 0.1% gelatin in PBS and incubate at 37 &#176;C for 4 h or at 4 &#176;C overnight. Remove the gelatin and allow it to dry under sterile laminar air flow.</li>
	<li>Prepare cell culture medium composed of 50 mL of DMEM supplemented with 10% fetal bovine serum (FBS) and 1% penicillin/streptomycin (P/S). Pre-warm it to 37 &#176;C.</li>
</ol>
2. Isolation of Neonatal Cardiomyocytes
<ol>
	<li>Sacrifice neonatal mice (1-2 days old) by decapitation with sterile scissors and open the chest along the sternum. Remove the heart using forceps while slightly pressing the thorax together and transfer the heart into a 24-well plate containing ice-cold HBSS (without Ca2+ and Mg2+).</li>
	<li>Remove non-cardiac tissue and larger vessels using sterile forceps. Transfer cleaned hearts into a 1.5 mL tube containing ice-cold HBSS. Use a maximum of 5 hearts per tube for enzymatic digestion.</li>
	<li>Mince the hearts with small scissors into &#60;0.5 to 1 mm&#179; pieces.</li>
	<li>Wash the minced hearts with HBSS two times by aspiration/addition of HBSS using a 1-mL microliter pipette. Remove the HBSS completely before adding the enzymes.</li>
	<li>For the enzymatic digestion of neonatal hearts, use a commercially available kit and follow the manufacturer&#39;s protocol (see the Table of Materials). Shake the tube containing the minced hearts every 5 min while incubating with enzymes at 37 &#176;C for 35 min.</li>
	<li>Seed suspended cells on non-coated cell culture dishes containing cell culture medium for 1.5-2 h to allow the adherence of the non-cardiomyocyte fraction. Repeat this step if a high purity of cardiomyocytes is needed. If desired, further culture the non-cardiomyocyte fraction. 
	NOTE: For a cell suspension of 15 hearts, the pre-plating step can be performed on 75 cm&#178; cell culture flasks. Usually, ~5 x 105 cells are obtained from one neonatal heart.</li>
	<li>Collect the supernatant in a 15 mL conical tube and centrifuge for 10 min at 300 x g. Resuspend the cells in 1 mL of cell culture medium.</li>
	<li>Count the cells with a Neubauer chamber hemocytometer, or use an equivalent method.</li>
	<li>Plate isolated cardiomyocytes on 6-well plates with a density of 3 x 105 cells/cm&#178;. Incubate the cells overnight at 37 &#176;C and 5% CO2. 
	NOTE: Optionally, cells can also be transfected at this point. However, increased viability was observed when the cells were cultured for one day before being subjected to electroporation.</li>
</ol>
3. Transfection with Fluorescently Labeled miRNA
<ol>
	<li>Pre-warm cell culture medium (see step 1.2) to 37 &#176;C in a water bath or an equivalent device.</li>
	<li>Prepare a 20 &#181;M stock solution of fluorescent miRNA in RNase-free sterile water.</li>
	<li>Prepare electroporation buffer containing 90 mM Na2HPO4, 90 mM NaH2PO4, 5 mM KCl, 10 mM MgCl2, and 10 mM sodium succinate and adjust the pH to 7.2; electroporation buffer can be stored at -20 &#176;C for several months.</li>
	<li>Detach the cells from the culture dish using 0.05% trypsin for 5 min. Inactivate the trypsin by adding cell culture medium.</li>
	<li>Count the cells with a Neubauer chamber hemocytometer, or use an equivalent method. Centrifuge the cells at 300 x g for 10 min.</li>
	<li>Resuspend the cells in electroporation buffer to obtain a concentration of 4 x 105 cells per 100 &#181;L.</li>
	<li>Mix 100 &#181;L of cell suspension with fluorescent miRNA (final concentration: 0.25 &#181;M) in a tube and load the mixture into an electroporation cuvette.
	<ol>
		<li>Empirically determine the appropriate amount of miRNA, depending upon cell type.</li>
	</ol>
	</li>
	<li>Perform electroporation using an electroporation device (see the Table of Materials), using the &#34;G-009&#34; program.</li>
	<li>Add 500 &#181;L of pre-warmed cell culture medium and transfer the whole cell suspension (4 x 105 cells) into a well of a 4-well glass-bottom chamber slide. Culture the cells for 1 day at 37 &#176;C in a 5% CO2 atmosphere. 
	NOTE: For FRAP analysis, a cell density of ~80% is optimal. The transfection of labeled miRNA should exclusively be performed using electroporation. Since the homogenous distribution of labeled miRNA molecules is beneficial for FRAP measurement, reagent-based transfection is not recommended.</li>
</ol>
4. Applying 3D-FRAP Microscopy (Day 3)
<ol>
	<li>Warm up the microscope incubator to 37 &#176;C and switch on the confocal microscope system at least 2 h before FRAP measurement to establish a thermal equilibrium and to decrease the possibility of drift. If possible, maintain a 5% CO2 atmosphere.</li>
	<li>Insert the chamber slide into the stage sample holder.</li>
	<li>Find a cluster of transfected cardiomyocytes using a 1.4 N.A. oil objective (400X magnification) and 561-nm laser excitation light at low laser power, with a detection range of 570-680 nm. 
	NOTE: The definition of FRAP settings, the image acquisition, and the analysis were done using microscope-specific software (see the Table of Materials).</li>
	<li>Activate the &#34;z-Stack,&#34; &#34;Time Series,&#34; &#34;Bleaching,&#34; and &#34;Regions&#34; buttons in the &#34;Setup Manager.&#34;</li>
	<li>Define the FRAP parameters.
	<ol>
		<li>Define the image acquisition settings in the &#34;Acquisition Mode&#34; menu by setting the &#34;frame size&#34; to 512 x 512, the &#34;line step&#34; to 1, and the &#34;scan time&#34; to &#60;1 s.</li>
		<li>In the &#34;Channels&#34; menu, adjust the laser power, offset, and gain settings to obtain maximal fluorescence from minimal laser excitation (e.g., laser power: 1-5%); adjust to avoid intensity saturation. Set the &#34;pinhole size&#34; to 2 &#181;m.</li>
		<li>Next, in the &#34;Regions&#34; menu, select the &#34;ROI drawing tool&#34; and use the cursor to mark the target cell, the reference cell, and the background area. If required, select several target cells for photobleaching.</li>
		<li>Adjust the photobleaching settings in the &#34;Bleaching&#34; menu (e.g., iterations: 9-14, laser power for photobleaching: 100%, interval of image acquisition: 60 s, cycles: 15). Define the start of bleaching after 3 initial scans.</li>
		<li>In the &#34;z-Stack&#34; menu, define the limits for z-stack acquisition, depending on the thickness of the cells. Adjust the &#34;number of z-layers&#34; to 12 - 15.</li>
		<li>Start the FRAP experiment and record the fluorescence recovery. 
		NOTE: Since the settings of a FRAP experiment depend upon the cell type, the fluorescent dye, and the microscope system, it is best to perform pilot experiments to determine the optimal parameters for FRAP. Bleaching should be sufficient to reduce the initial fluorescence intensity by at least 50%. Typically, fluorescence recovery should be recorded every 30-60 s until the plateau phase is reached.</li>
	</ol>
	</li>
</ol>
5. Data Analysis
<ol>
	<li>Create maximum projections of the acquired z-stacks and obtain fluorescence intensity values of the bleached target cells, the reference cell, and the background. Using microscope-specific software, click &#34;Processing&#34;&#160;&#8594; &#34;Maximum intensity projection&#34; &#8594; select file &#8594; &#34;Apply.&#34;
	<ol>
		<li>Alternatively, use an equivalent image analyzing tool (e.g., ImageJ).</li>
	</ol>
	</li>
	<li>Copy the fluorescence intensity data at all time points from the target cell, the background, and the reference cell into a spreadsheet.
	<ol>
		<li>Subtract the background intensity and the intensity of the reference cell from the intensity values of the target cell to correct for photobleaching caused during the acquisition process. Perform background and reference cell corrections for each time point.</li>
		<li>Normalize the corrected FRAP data to the initial fluorescence intensity before bleaching by dividing each value by the initial fluorescence.</li>
		<li>To obtain FRAP curves, set the baseline to the fluorescence intensity immediately after the bleach by subtracting from the intensity values of each time point.</li>
	</ol>
	</li>
</ol>

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The authors declare no conflict of interest.

miRNAs are key players in cellular physiology and were shown to act as signaling molecules by using&#8212;among others&#8212;GJs as a pathway for intercellular exchange11,12,22. The current protocol presents an in vitro live-cell imaging technique to characterize this GJ-dependent shuttling using fluorescent miRNAs within cell clusters.
The protocol was developed on cardiomyocytes as a cell m...

Small noncoding RNAs are important players in cellular gene regulation. These molecules are composed of 20-25 nucleotides that bind to a specific target mRNA, leading to the blockage of translation or to mRNA degradation1,2. The gene regulatory process undertaken by small RNAs, such as miRNA and siRNA, is a highly conserved mechanism that has been found in many different species3. In particular, miRNA molecules are of crucial importance to a variety of physiological processes, including proliferation, differentiation, and regeneration4,5. In addition, the dysregulation of miRNA expression is attributed to many pathological disorders. Correspondingly, miRNAs have been demonstrated to be suitable as biomarkers for diagnosis and as therapeutic agents for gene therapy6,7.
Gap junctions (GJs) are specialized protein structures in the plasma membrane of two adjacent cells that allow the diffusional exchange of molecules with a molecular weight of up to 1 kD. They have been shown to be important to tissue development, differentiation, cell death, and pathological disorders such as cancer or cardiovascular disease8,9,10. Several molecules have been described as being capable of crossing GJ channels, including ions, metabolites, and nucleotides. Interestingly, GJs were also found to provide a pathway for the intercellular movement of small RNAs11,12. Thus, miRNAs can act not only within the cell in which they are produced, but also within recipient cells. This highlights the role of miRNAs in the intercellular signal transduction system. At the same time, the data demonstrate that gap junctional intercellular communication is closely linked to miRNA function. Because of the significant impact of miRNA and GJs on tissue homeostasis, pathology, and diagnosis, a comprehensive understanding of the function of GJs and the related intercellular dynamics of miRNA will help to clarify the mechanisms of miRNA-based diseases and to develop new strategies for miRNA therapies.
Depending on the extent of gap junctional coupling, the transfer of miRNA molecules between cells can be a very rapid process. Therefore, a methodology that allows the visualization and quantification of the fast intercellular movement of these regulatory signaling molecules is required. Commonly, flow cytometry and molecular biological techniques have been applied to demonstrate the shuttling of small RNAs11,12,13,14. However, as opposed to FRAP microscopy, these approaches lack high temporal resolution, which is mandatory when analyzing the exchange of miRNA via GJs. Moreover, FRAP microscopy is less invasive and therefore represents a powerful and novel live-cell imaging technique to evaluate the GJ-dependent exchange of molecules in several cell types15,16,17.
Here, we present a detailed protocol describing the application of 3D-FRAP to assess miRNA shuttling between cardiomyocytes. For this purpose, cardiomyocytes were transfected with fluorescently labeled miRNA. A cell marked with this miRNA was photobleached, and the gap junctional miRNA re-influx from adjacent cells was recorded in a time-dependent manner. The high temporal resolution of FRAP experiments offers the possibility to perform kinetic studies for the precise evaluation of the intercellular transfer of miRNA and siRNA between living cells. Moreover, as small RNAs can be exchanged via different mechanisms with highly different kinetics, FRAP microscopy can help to clarify the extent to which GJs are involved in the respective shuttling processes18. In addition, 3D-FRAP can be used to investigate physiological and pathological alterations in GJ permeability and its impact on small RNA transfer15,19.

<table border="0" cellpadding="0" cellspacing="0" width="698">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">neonatal NMRI mice</td>
			<td style="width:159px;">Charles River</td>
			<td style="width:119px;"></td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Gelatin</td>
			<td style="width:159px;">Sigma Aldrich</td>
			<td style="width:119px;">G7041</td>
			<td style="width:179px;">0.1% solution in PBS, sterilized</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">PBS</td>
			<td style="width:159px;">Pan Biotech</td>
			<td style="width:119px;">P04-53500</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Dulbecco&#180;s modified medium</td>
			<td style="width:159px;">Pan Biotech</td>
			<td style="width:119px;">P04-03550</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Penicillin/Streptomycin</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">15140122</td>
			<td style="width:179px;">100 U/ml, 100&#181;g/ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Fetal bovine serum</td>
			<td style="width:159px;">Pan Biotech</td>
			<td style="width:119px;">P30-3306</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Cell culture plastic</td>
			<td style="width:159px;">TPP</td>
			<td style="width:119px;"></td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Primary Cardiomyocyte Isolation Kit</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">88281</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:243px;">HBSS</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">88281</td>
			<td style="width:179px;">included in primary cardiomyocyte isolation kit</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Trypan blue</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">15250061</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:243px;">miRIDIAN Dy547 labeled microRNA Mimic&#160;</td>
			<td style="width:159px;">Dharmacon</td>
			<td style="width:119px;">CP-004500-01-05</td>
			<td style="width:179px;">dissolve in RNAse free water, stock solution 20&#181;M</td>
		</tr>
		<tr height="33">
			<td height="33" style="height:33px;width:243px;">Sodium phosphate monobasic</td>
			<td style="width:159px;">Sigma</td>
			<td style="width:119px;">S3139</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Sodium phosphate dibasic</td>
			<td style="width:159px;">Carl Roth</td>
			<td style="width:119px;">T877.2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Potassium chloride</td>
			<td style="width:159px;">Sigma</td>
			<td style="width:119px;">P9333</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Magnesium chloride</td>
			<td style="width:159px;">Serva</td>
			<td style="width:119px;">28305.01</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Sodium succinate</td>
			<td style="width:159px;">Carl Roth</td>
			<td style="width:119px;">3195.1</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">0.05% Trypsin/EDTA solution</td>
			<td style="width:159px;">Merck</td>
			<td style="width:119px;">L2153</td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">4-well- Glass bottom chamber slides</td>
			<td style="width:159px;">IBIDI</td>
			<td style="width:119px;">80827</td>
			<td style="width:179px;">coat with 0.1% gelatin solution</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Amaxa Nucleofector II</td>
			<td style="width:159px;">Lonza</td>
			<td style="width:119px;"></td>
			<td style="width:179px;">program G-009 was used for Electroporation&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">LSM 780 ELYRA PS.1 system</td>
			<td style="width:159px;">Zeiss</td>
			<td style="width:119px;"></td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Excel software</td>
			<td style="width:159px;">Microsoft</td>
			<td style="width:119px;"></td>
			<td style="width:179px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">&#945;-actinin antibody</td>
			<td style="width:159px;">Abcam</td>
			<td style="width:119px;">ab9465</td>
			<td style="width:179px;">dilution 1:200</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Connexin43 antibody</td>
			<td style="width:159px;">Santa Cruz</td>
			<td style="width:119px;">sc-9059</td>
			<td style="width:179px;">dilution 1:200</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">goat anti-mouse Alexa 594 antibody</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td>A-11005</td>
			<td>dilution 1:300</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">goat anti-rabbit Alexa 488 antibody&#160;</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td>A-11034</td>
			<td>dilution 1:300</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Connexin43 siRNA</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">AM16708 ID158724</td>
			<td>&#160;final concentration 250nM</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:243px;">Near-IR Live/Dead Cell Stain Kit</td>
			<td style="width:159px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">L10119</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">CellTrace Calcein Red-Orange</td>
			<td style="width:159px;">Thermo Scientific</td>
			<td style="width:119px;">C34851</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">DAPI nuclear stain</td>
			<td style="width:159px;">Thermo Scientific</td>
			<td style="width:119px;">D1306</td>
			<td style="width:179px;"></td>
		</tr>
	</tbody>
</table>

analysis of the gap junction-dependent transfer of mirna with 3d-frap microscopy

Small antisense RNAs, like miRNA and siRNA, play an important role in cellular physiology and pathology and, moreover, can be used as therapeutic agents in the treatment of several diseases. The development of new, innovative strategies for miRNA/siRNA therapy is based on an extensive knowledge of the underlying mechanisms. Recent data suggest that small RNAs are exchanged between cells in a gap junction-dependent manner, thereby inducing gene regulatory effects in the recipient cell. Molecular biological techniques and flow cytometric analysis are commonly used to study the intercellular exchange of miRNA. However, these methods do not provide high temporal resolution, which is necessary when studying the gap junctional flux of molecules. Therefore, to investigate the impact of miRNA/siRNA as intercellular signaling molecules, novel tools are needed that will allow for the analysis of these small RNAs at the cellular level. The present protocol describes the application of three-dimensional fluorescence recovery after photobleaching (3D-FRAP) microscopy to elucidating the gap junction-dependent exchange of miRNA molecules between cardiac cells. Importantly, this straightforward and non-invasive live-cell imaging approach allows for the visualization and quantification of the gap junctional shuttling of fluorescently labeled small RNAs in real time, with high spatio-temporal resolution. The data obtained by 3D-FRAP confirm a novel pathway of intercellular gene regulation, where small RNAs act as signaling molecules within the intercellular network.

Here, we present 3D-FRAP microscopy as a non-invasive technique to study the gap junctional shuttling of fluorescent miRNA within neonatal cardiomyocytes. The isolated cardiomyocytes revealed the typical striated &#945;-actinin pattern and contained large plaques of Cx43 along the cell-cell borders (Figure 1A, white arrowheads), which allowed for the high intercellular flux of molecules. The purity of isolated cardiomyocytes was assessed by the microscopic qu...

Watch this Scientific Journal Video about Analysis of the Gap Junction-dependent Transfer of miRNA with 3D-FRAP Microscopy at JoVE.com

Analysis of the Gap Junction-dependent Transfer of miRNA with 3D-FRAP Microscopy

Here, we describe the application of three-dimensional fluorescence recovery after photobleaching (3D-FRAP) for the analysis of the gap junction-dependent shuttling of miRNA. In contrast to commonly applied methods, 3D-FRAP allows for the quantification of the intercellular transfer of small RNAs in real time, with high spatio-temporal resolution.

Small antisense RNAs, like miRNA and siRNA, play an important role in cellular physiology and pathology and, moreover, can be used as therapeutic agents ...

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Research

JoVE Journal

Biology

8.7K Views.  Reference and Translation Center for Cardiac Stem Cell Therapy (RTC). Here, we describe the application of three-dimensional fluorescence recovery after photobleaching (3D-FRAP) for the analysis of the gap junction-dependent shuttling of miRNA. In contrast to commonly applied methods, 3D-FRAP allows for the quantification of the intercellular transfer of small RNAs in real time, with high spatio-temporal resolution.

Video: Analysis of the Gap Junction-dependent Transfer of miRNA with 3D-FRAP Microscopy

Intravital Microscopy of the Microcirculation in the Mouse Cremaster Muscle for the Analysis of Peripheral Stem Cell Migration

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to nonmarrow tissue have not been completely clarified. We describe here the technique of intravital microscopy applied to the mouse cremaster microcirculation for analysis of peripheral bone marrow stem cell migration in vivo. Intravital microscopy of the M. cremaster has been previously introduced in the field of inflammatory research for direct observation of leucocyte interaction with the vascular endothelium. Since sufficient peripheral stem and progenitor cell migration includes similar initial steps of rolling along and firm adhesion at the endothelial lining it is conceivable to apply the M. cremaster model for the observation and quantification of the interaction of intravasculary administered stem cells with the endothelium. As various chemical components can be selectively applied to the target tissue by simple superfusion techniques, it is possible to establish essential microenvironmental preconditions, for initial stem cell recruitment to take place in a living organism outside the bone marrow.

Intravital microscopy of the mouse M. cremaster microcirculation offers a unique and well-standardized in vivo model for the analysis of peripheral bone marrow stem cell migration.

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to ...

The Xenopus Oocyte Cut-open Vaseline Gap Voltage-clamp Technique With Fluorometry

The cut-open oocyte Vaseline gap (COVG) voltage clamp technique allows for analysis of electrophysiological and kinetic properties of heterologous ion channels in oocytes. Recordings from the cut-open setup are particularly useful for resolving low magnitude gating currents, rapid ionic current activation, and deactivation. The main benefits over the two-electrode voltage clamp (TEVC) technique include increased clamp speed, improved signal-to-noise ratio, and the ability to modulate the intracellular and extracellular milieu.
Here, we employ the human cardiac sodium channel (hNaV1.5), expressed in Xenopus oocytes, to demonstrate the cut-open setup and protocol as well as modifications that are required to add voltage clamp fluorometry capability.
The properties of fast activating ion channels, such as hNaV1.5, cannot be fully resolved near room temperature using TEVC, in which the entirety of the oocyte membrane is clamped, making voltage control difficult. However, in the cut-open technique, isolation of only a small portion of the cell membrane allows for the rapid clamping required to accurately record fast kinetics while preventing channel run-down associated with patch clamp techniques.
In conjunction with the COVG technique, ion channel kinetics and electrophysiological properties can be further assayed by using voltage clamp fluorometry, where protein motion is tracked via cysteine conjugation of extracellularly applied fluorophores, insertion of genetically encoded fluorescent proteins, or the incorporation of unnatural amino acids into the region of interest1. This additional data yields kinetic information about voltage-dependent conformational rearrangements of the protein via changes in the microenvironment surrounding the fluorescent molecule.

The Xenopus Oocyte Cut-open Vaseline Gap Voltage-clamp Technique With Fluorometry

The cut-open Vaseline gap approach is used to obtain low noise recordings of ionic and gating currents from voltage-dependent ion channels expressed in Xenopus oocytes with high resolution of fast channel kinetics. With minor modification, voltage clamp fluorometry can be coupled to the cut-open oocyte protocol.

The cut-open oocyte Vaseline gap (COVG) voltage clamp technique allows for analysis of electrophysiological and kinetic properties of heterologous ion ...

Rapid Analysis and Exploration of Fluorescence Microscopy Images

Despite rapid advances in high-throughput microscopy, quantitative image-based assays still pose significant challenges. While a variety of specialized image analysis tools are available, most traditional image-analysis-based workflows have steep learning curves (for fine tuning of analysis parameters) and result in long turnaround times between imaging and analysis. In particular, cell segmentation, the process of identifying individual cells in an image, is a major bottleneck in this regard.
Here we present an alternate, cell-segmentation-free workflow based on PhenoRipper, an open-source software platform designed for the rapid analysis and exploration of microscopy images. The pipeline presented here is optimized for immunofluorescence microscopy images of cell cultures and requires minimal user intervention. Within half an hour, PhenoRipper can analyze data from a typical 96-well experiment and generate image profiles. Users can then visually explore their data, perform quality control on their experiment, ensure response to perturbations and check reproducibility of replicates. This facilitates a rapid feedback cycle between analysis and experiment, which is crucial during assay optimization. This protocol is useful not just as a first pass analysis for quality control, but also may be used as an end-to-end solution, especially for screening. The workflow described here scales to large data sets such as those generated by high-throughput screens, and has been shown to group experimental conditions by phenotype accurately over a wide range of biological systems. The PhenoBrowser interface provides an intuitive framework to explore the phenotypic space and relate image properties to biological annotations. Taken together, the protocol described here will lower the barriers to adopting quantitative analysis of image based screens.

Here we describe a workflow for rapidly analyzing and exploring collections of fluorescence microscopy images using PhenoRipper, a recently developed image-analysis platform.

Despite rapid advances in high-throughput microscopy, quantitative image-based assays still pose significant challenges. While a variety of specialized ...

Analysis of Autophagy in Penicillium chrysogenum by Using Starvation Pads in Combination With Fluorescence Microscopy

The study of cellular quality control systems has emerged as a highly dynamic and relevant field of contemporary research. It has become clear that cells possess several lines of defense against damage to biologically relevant molecules like nucleic acids, lipids and proteins. In addition to organelle dynamics (fusion/fission/motility/inheritance) and tightly controlled protease activity, the degradation of surplus, damaged or compromised organelles by autophagy (cellular &#8216;self-eating&#8217;) has received much attention from the scientific community. The regulation of autophagy is quite complex and depends on genetic and environmental factors, many of which have so far not been elucidated. Here a novel method is presented that allows the convenient study of autophagy in the filamentous fungus Penicillium chrysogenum. It is based on growth of the fungus on so-called &#8216;starvation pads&#8217; for stimulation of autophagy in a reproducible manner. Samples are directly assayed by microscopy and evaluated for autophagy induction / progress. The protocol presented here is not limited for use with P. chrysogenum and can be easily adapted for use in other filamentous fungi.

Analysis of Autophagy in Penicillium chrysogenum by Using Starvation Pads in Combination With Fluorescence Microscopy

A convenient and powerful method for studying autophagy in Penicillium chrysogenum by using starvation pads (mixtures of agarose and tap water in a microscope slide containing a central cavity) is presented here.

The study of cellular quality control systems has emerged as a highly dynamic and relevant field of contemporary research. It has become clear that cells ...

Detection of miRNA Targets in High-throughput Using the 3'LIFE Assay

Luminescent Identification of Functional Elements in 3&#8217;UTRs (3&#8217;LIFE) allows the rapid identification of targets of specific miRNAs within an array of hundreds of queried 3&#8217;UTRs. Target identification is based on the dual-luciferase assay, which detects binding at the mRNA level by measuring translational output, giving a functional readout of miRNA targeting. 3&#8217;LIFE uses non-proprietary buffers and reagents, and publically available reporter libraries, making genome-wide screens feasible and cost-effective. 3&#8217;LIFE can be performed either in a standard lab setting or scaled up using liquid handling robots and other high-throughput instrumentation. We illustrate the approach using a dataset of human 3&#8217;UTRs cloned in 96-well plates, and two test miRNAs, let-7c and miR-10b. We demonstrate how to perform DNA preparation, transfection, cell culture and luciferase assays in 96-well format, and provide tools for data analysis. In conclusion 3&#39;LIFE is highly reproducible, rapid, systematic, and identifies high confidence targets.

Luminescent identification of functional elements in 3&#8217; untranslated regions (3&#8217;UTRs) (3&#8217;LIFE) is a technique to identify functional regulation in 3&#8217;UTRs by miRNAs or other regulatory factors. This protocol utilizes high-throughput methodology such as 96-well transfection and luciferase assays to screen hundreds of putative interactions for functional repression.

Luminescent Identification of Functional Elements in 3&#8217;UTRs (3&#8217;LIFE) allows the rapid identification of targets of specific miRNAs within an ...

Real-time Imaging of Plant Cell Surface Dynamics with Variable-angle Epifluorescence Microscopy

A plant&#8217;s cell surface is its interface for perceiving environmental cues; it responds with cell biological changes such as membrane trafficking and cytoskeletal rearrangement. Real-time and high-resolution image analysis of such intracellular events will increase the understanding of plant cell biology at the molecular level. Variable angle epifluorescence microscopy (VAEM) is an emerging technique that provides high-quality, time-lapse images of fluorescently-labeled proteins on the plant cell surface. In this article, practical procedures are described for VAEM specimen preparation, adjustment of the VAEM optical system, movie capturing and image analysis. As an example of VAEM observation, representative results are presented on the dynamics of PATROL1. This is a protein essential for stomatal movement, thought to be involved in proton pump delivery to plasma membranes in the stomatal complex of Arabidopsis thaliana. VAEM real-time observation of guard cells and subsidiary cells in A. thaliana cotyledons showed that fluorescently-tagged PATROL1 appeared as dot-like structures on plasma membranes for several seconds and then disappeared. Kymograph analysis of VAEM movie data determined the time distribution of the presence (termed &#8216;residence time&#8217;) of the dot-like structures. The use of VAEM is discussed in the context of this example.

The goal of this protocol is to demonstrate how to monitor fluorescently-tagged protein dynamics on plant cell surfaces with variable-angle epifluorescence microscopy, showing blinking dots of GFP-tagged PATROL1, a membrane trafficking protein, in the cell cortex of the stomatal complex in Arabidopsis thaliana.

A plant&#8217;s cell surface is its interface for perceiving environmental cues; it responds with cell biological changes such as membrane trafficking and ...

Open-source Single-particle Analysis for Super-resolution Microscopy with VirusMapper

Super-resolution fluorescence microscopy is currently revolutionizing cell biology research. Its capacity to break the resolution limit of around 300 nm allows for the routine imaging of nanoscale biological complexes and processes. This increase in resolution also means that methods popular in electron microscopy, such as single-particle analysis, can readily be applied to super-resolution fluorescence microscopy. By combining this analytical approach with super-resolution optical imaging, it becomes possible to take advantage of the molecule-specific labeling capacity of fluorescence microscopy to generate structural maps of molecular elements within a metastable structure. To this end, we have developed a novel algorithm &#8212; VirusMapper &#8212; packaged as an easy-to-use, high-performance, and high-throughput ImageJ plugin. This article presents an in-depth guide to this software, showcasing its ability to uncover novel structural features in biological molecular complexes. Here, we present how to assemble compatible data and provide a step-by-step protocol on how to use this algorithm to apply single-particle analysis to super-resolution images.

This manuscript uses the Fiji-based open-source software package VirusMapper to apply single-particle analysis to super-resolution microscopy images in order to generate precise models of nanoscale structure.

Super-resolution fluorescence microscopy is currently revolutionizing cell biology research. Its capacity to break the resolution limit of around 300 nm ...

Biological Sample Preparation by High-pressure Freezing, Microwave-assisted Contrast Enhancement, and Minimal Resin Embedding for Volume Imaging

The described sample preparation technique is designed to combine the best quality of ultrastructural preservation with the most suitable contrast for the imaging modality in a focused ion beam scanning electron microscope (FIB-SEM), which is used to obtain stacks of sequential images for 3D reconstruction and modelling. High-pressure freezing (HPF) allows close to native structural preservation, but the subsequent freeze substitution often does not provide sufficient contrast, especially for a bigger specimen, which is needed for high-quality imaging in the SEM required for 3D reconstruction. Therefore, in this protocol, after the freeze substitution, additional contrasting steps are carried out at room temperature. Although these steps are performed in a microwave, it is also possible to follow traditional bench processing, which requires longer incubation times.The subsequent embedding in minimal amounts of resin allows for faster and more precise targeting and preparation inside the FIB-SEM. This protocol is especially useful for samples that require preparation by high-pressure freezing for a reliable ultrastructural preservation but do not gain enough contrast during the freeze substitution for volume imaging using FIB-SEM. In combination with the minimal resin embedding, this protocol provides an efficient workflow for the acquisition of high-quality volume data.

Here we present a protocol for combining two sample processing techniques, high-pressure freezing and microwave-assisted sample processing, followed by minimal resin embedding for acquiring data with a focused ion beam scanning electron microscope (FIB-SEM). This is demonstrated using a mouse tibial nerve sample and Caenorhabditis elegans.

The described sample preparation technique is designed to combine the best quality of ultrastructural preservation with the most suitable contrast for the ...

Oligomerization Dynamics of Cell Surface Receptors in Living Cells by Total Internal Reflection Fluorescence Microscopy Combined with Number and Brightness Analysis

Despite the importance and ubiquity of receptor oligomerization, few methods are applicable for detecting clustering events and measuring the degree of clustering. Here, we describe an imaging approach to determine the average oligomeric state of mEGFP-tagged-receptor homocomplexes in the membrane of living cells. The protocol is based on Total Internal Reflection Fluorescence (TIRF) microscopy combined with Number and Brightness (N&#38;B) analysis. N&#38;B is a method similar to fluorescence-correlation spectroscopy (FCS) and photon counting histogram (PCH), which are based on the statistical analysis of the fluctuations of the fluorescence intensity of fluorophores diffusing in and out of an illumination volume during an observation time. In particular, N&#38;B is a simplification of PCH to obtain information on the average number of proteins in oligomeric mixtures. The intensity fluctuation amplitudes are described by the molecular brightness of the fluorophore and the average number of fluorophores within the illumination volume. Thus, N&#38;B considers only the first and second moments of the amplitude distribution, namely, the mean intensity and the variance. This is, at the same time, the strength and the weakness of the method. Because only two moments are considered, N&#38;B cannot determine the molar fraction of unknown oligomers in a mixture, but it only estimates the average oligomerization state of the mixture. Nevertheless, it can be applied to relatively small time series (compared to other moment methods) of images of live cells on a pixel-by-pixel basis, simply by monitoring the time fluctuations of the fluorescence intensity. It reduces the effective time-per-pixel to a few microseconds, allowing acquisition in the time range of seconds to milliseconds, which is necessary for fast oligomerization kinetics. Finally, large cell areas as well as sub-cellular compartments can be explored.

We describe an imaging approach for the determination of the average oligomeric state of mEGFP-tagged-receptor oligomers induced by ligand binding in the plasma membrane of living cells. The protocol is based on Total Internal Reflection Fluorescence (TIRF) microscopy combined with Number and Brightness (N&#38;B) analysis.

Despite the importance and ubiquity of receptor oligomerization, few methods are applicable for detecting clustering events and measuring the degree of ...

Tethered Bilayer Lipid Membranes to Monitor Heat Transfer between Gold Nanoparticles and Lipid Membranes

Here we report a protocol to investigate the heat transfer between irradiated gold nanoparticles (GNPs) and bilayer lipid membranes by electrochemistry using tethered bilayer lipid membranes (tBLMs) assembled on gold electrodes. Irradiated modified GNPs, such as streptavidin-conjugated GNPs, are embedded in tBLMs containing target molecules, such as biotin. By using this approach, the heat transfer processes between irradiated GNPs and model bilayer lipid membrane with entities of interest are mediated by a horizontally focused laser beam. The thermal predictive computational model is used to confirm the electrochemically induced conductance changes in the tBLMs. Under the specific conditions used, detecting heat pulses required specific attachment of the gold nanoparticles to the membrane surface, while unbound gold nanoparticles failed to elicit a measurable response. This technique serves as a powerful detection biosensor which can be directly utilized for the design and development of strategies for thermal therapies that permits optimization of the laser parameters, particle size, particle coatings and composition.

This work outlines a protocol to achieve dynamic, non-invasive monitoring of heat transfer from laser-irradiated gold nanoparticles to tBLMs. The system combines impedance spectroscopy for the real-time measurement of conductance changes across the tBLMs, with a horizontally focused laser beam that drives gold nanoparticle illumination, for heat production.

Here we report a protocol to investigate the heat transfer between irradiated gold nanoparticles (GNPs) and bilayer lipid membranes by electrochemistry ...