We thank J. Schmidt from the University of Freiburg for constructing the device. We thank P. Nielsen and D. Medgyesi for their support and critical reading of this manuscript. This study was supported by the Deutsche Forschungsgemeinschaft through SFB746 and by the Excellence Initiative of the German Research Foundation (GSC-4, Spemann Graduate School).

1. Designing and Building the Device
<ol>
	<li>Pilot Experiments 
	NOTE: The required light intensity for a specific optogenetic tool and cell type may vary significantly. Pilot experiments with prototypes are useful to estimate the minimal light intensity necessary. The optogenetic tool used for the following experiments is a Dronpa-Linker-Dronpa fusion construct. The Dronpa sequence was commercially obtained (See List of Materials). A long linker was cloned in between two Dronpa sequences to all...

<ol>
	<li>Dugue, G. P., Akemann, W., Knopfel, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comprehensive+concept+of+optogenetics.">A comprehensive concept of optogenetics.</a> Prog Brain Res. 196, 1-28 (2012).</li><li>Tischer, D., Weiner, O. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Illuminating+cell+signalling+with+optogenetic+tools.">Illuminating cell signalling with optogenetic tools.</a> Nat Rev Mol Cell Biol. 15 (8), 551-558 (2014).</li><li>Toettcher, J. E., Voigt, C. A., Weiner, O. D., Lim, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+promise+of+optogenetics+in+cell+biology:+interrogating+molecular+circuits+in+space+and+time.">The promise of optogenetics in cell biology: interrogating molecular circuits in space and time.</a> Nat Methods. 8 (1), 35-38 (2011).</li><li>Zhang, K., Cui, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optogenetic+control+of+intracellular+signaling+pathways.">Optogenetic control of intracellular signaling pathways.</a> Trends Biotechnol. 33 (2), 92-100 (2015).</li><li>Bugaj, L. J., Choksi, A. T., Mesuda, C. K., Kane, R. S., Schaffer, D. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optogenetic+protein+clustering+and+signaling+activation+in+mammalian+cells.">Optogenetic protein clustering and signaling activation in mammalian cells.</a> Nat Methods. 10 (3), 249-252 (2013).</li><li>Bugaj, L. J., 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=Regulation+of+endogenous+transmembrane+receptors+through+optogenetic+Cry2+clustering.">Regulation of endogenous transmembrane receptors through optogenetic Cry2 clustering.</a> Nat Commun. 6, 6898 (2015).</li><li>Strickland, D., 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=TULIPs:+tunable,+light-controlled+interacting+protein+tags+for+cell+biology.">TULIPs: tunable, light-controlled interacting protein tags for cell biology.</a> Nat Methods. 9 (4), 379-384 (2012).</li><li>Taslimi, 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=An+optimized+optogenetic+clustering+tool+for+probing+protein+interaction+and+function.">An optimized optogenetic clustering tool for probing protein interaction and function.</a> Nat Commun. 5, 4925 (2014).</li><li>Toettcher, J. E., Gong, D., Lim, W. A., Weiner, O. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Light-based+feedback+for+controlling+intracellular+signaling+dynamics.">Light-based feedback for controlling intracellular signaling dynamics.</a> Nat Methods. 8 (10), 837-839 (2011).</li><li>Toettcher, J. E., Weiner, O. D., Lim, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+optogenetics+to+interrogate+the+dynamic+control+of+signal+transmission+by+the+Ras/Erk+module.">Using optogenetics to interrogate the dynamic control of signal transmission by the Ras/Erk module.</a> Cell. 155 (6), 1422-1434 (2013).</li><li>Wang, J., 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=Utilization+of+a+photoactivatable+antigen+system+to+examine+B-cell+probing+termination+and+the+B-cell+receptor+sorting+mechanisms+during+B-cell+activation.">Utilization of a photoactivatable antigen system to examine B-cell probing termination and the B-cell receptor sorting mechanisms during B-cell activation.</a> Proc Natl Acad Sci U S A. 113 (5), E558-E567 (2016).</li><li>Wend, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optogenetic+control+of+protein+kinase+activity+in+mammalian+cells.">Optogenetic control of protein kinase activity in mammalian cells.</a> ACS Synth Biol. 3 (5), 280-285 (2014).</li><li>Zhou, X. X., Chung, H. K., Lam, A. J., Lin, M. Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+control+of+protein+activity+by+fluorescent+protein+domains.">Optical control of protein activity by fluorescent protein domains.</a> Science. 338 (6108), 810-814 (2012).</li><li>Baumgarth, N., Roederer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+practical+approach+to+multicolor+flow+cytometry+for+immunophenotyping.">A practical approach to multicolor flow cytometry for immunophenotyping.</a> J Immunol Methods. 243 (1-2), 77-97 (2000).</li><li>Givan, A. 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The LED Thermo Flow is an innovative device to study optogenetic tools in a flow cytometer.
So far, optogenetic samples have been illuminated only with microscopy lasers or flashlight devices11,12. Depending on the angle and distance of the flashlight to the sample, substantial variability in the amount of illumination is expected between experiments. Furthermore, there is a limit to the number of flashlights a single person can operate in an experiment. This restricts the experimen...

Optogenetic tools have been gaining popularity, in part because they can be used to decipher the wiring of signaling pathways1-4. They are based on the ability of photoactivatable proteins to change their conformation and binding affinity when illuminated with light. Fusing these proteins to signaling elements allows for the specific regulation of a single player within complex intracellular signaling pathways5-12. Consequently, a signaling pathway can be studied with high temporal and spatial resolution.
Most cell-based optogenetic studies utilize microscopy-based methods combined with culturing in the presence of light, followed by biochemical analysis11,12. In contrast, a flow cytometer singularizes cells along a capillary and measures cell size, granularity and fluorescence intensities. This method has major advantages over microscopy or biochemical methods, including the ability to analyze thousands of living cells at single-cell resolution in a very short time. Hence, it is desirable to combine optogenetics with flow cytometry.
To our knowledge, there is no established protocol for optogenetic flow cytometry. A broadly accepted procedure is to manually illuminate cells from outside the reaction tube with flashlight devices. However, manual illumination in the flow cytometer requires the light to pass through the reaction tube and, for live cell imaging, a cylindrical, heated water chamber. This causes substantial light scattering and loss of light. Moreover, the light intensity provided by manual illumination is not reproducible between experiments (angle, distance, etc.) and there is a practical limit to the number of wavelengths in one experiment.
By constructing the LED Thermo Flow device, we were able to overcome these limitations. With this device, cells can be illuminated with specific wavelengths in a temperature-controlled manner during flow cytometric measurements. This allows for precise and reproducible amounts of light within and between experiments.
To demonstrate the utility of our device in vivo, we recorded the fluorescence signal of Dronpa in Ramos B cells during photoswitching. Ramos B cells are derived from a human Burkitt&#39;s lymphoma. Dronpa is a fluorescent protein that exists as a monomer, dimer or tetramer. In its monomeric form, it is non-fluorescent. Illumination with 400 nm light induces dimerization and tetramerization and renders the Dronpa protein fluorescent. This process can be reversed by illumination with 500 nm light. The Dronpa protein has been used to control the function and location of signaling proteins4,13.
Here, we expressed a Dronpa-Linker-Dronpa protein in Ramos B cells to study photoswitching of Dronpa in a flow cytometer. Using our device, we were able to efficiently and reproducibly photoswitch Dronpa while recording its fluorescence intensity in real time. This method provides substantial advantages over current illumination protocols with manual illumination and significantly broadens the experimental repertoire for optogenetic tools and cage compounds. Using our device will significantly simplify and accelerate the discovery and development of novel optogenetic tools.

<table border="0" cellpadding="0" cellspacing="0" width="1212">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Glass FACS tube</td>
			<td style="width:357px;">&#160;Thermo Fisher Scientific; Waltham, USA</td>
			<td style="width:312px;">14-961-26</td>
			<td style="width:296px;">Borosilicate glass tubes 12x75 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Flow Cytometer</td>
			<td style="width:357px;">BD Bioscienceg; Heidelberg, Germany</td>
			<td style="width:312px;">Fortessa II</td>
			<td>Special Order</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Dronpa: pcDNA3-mNeptune2-N</td>
			<td style="width:357px;">Addgene; Cambridge, USA</td>
			<td style="width:312px;">41645</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">PolyJet</td>
			<td style="width:357px;">SignaGen, Rockville, USA</td>
			<td style="width:312px;">SL100688</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">LED 505 nm</td>
			<td style="width:357px;">Avago Technologies; Boeblingen, Germany</td>
			<td style="width:312px;">HLMP-CE34-Y1CDD</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">LED 400 nm</td>
			<td style="width:357px;">Avago Technologies; Boeblingen, Germany</td>
			<td style="width:312px;">UV5TZ-400-15</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Plexiglas tube 15 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">76999</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Plexiglas 3 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">692230</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Plexiglas 2,5 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">692225</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Plexiglas 1,5 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">692215</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">PVC tile 5 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">690020.005</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">PVC tile 6 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">690020.006</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">PVC block 50 mm</td>
			<td style="width:357px;">Maertin; Freiburg, Germany</td>
			<td style="width:312px;">690020.050</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">RPMI</td>
			<td style="width:357px;">Invitrogen, Life Technologies; Darmstadt, Germany</td>
			<td style="width:312px;">61870-010</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">2-Mercaptoethanol</td>
			<td style="width:357px;">EMD; Germany</td>
			<td style="width:312px;">805740</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">FCS</td>
			<td style="width:357px;">PAN Biotech; Aidenbach, Germany</td>
			<td style="width:312px;">P30-3302</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Penicillin/Strptomycin (10000 U/ml)</td>
			<td style="width:357px;">Invitrogen, Life Technologies; Darmstadt, Germany</td>
			<td style="width:312px;">15140-122</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Acrifix plexiglas glue</td>
			<td style="width:357px;">Evonic industries, Essen, Germany</td>
			<td style="width:312px;">1R0192</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Tangit PVC-U glue</td>
			<td style="width:357px;">Henkel, D&#252;sseldorf, Germany</td>
			<td style="width:312px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

led thermo flow &#8212; combining optogenetics with flow cytometry

Optogenetic tools allow isolated, functional investigations of almost any signaling molecule within complex signaling pathways. A major obstacle is the controlled delivery of light to the cell sample and hence the most popular tools for optogenetic studies are microscopy-based cell analyses and in vitro experiments. The flow cytometer has major advantages over a microscope, including the ability to rapidly measure thousands of cells at single cell resolution. However, it is not yet widely used in optogenetics. Here, we present a device that combines the power of optogenetics and flow cytometry: the LED Thermo Flow. This device illuminates cells at specific wavelengths, light intensities and temperatures during flow cytometric measurements. It can be built at low cost and be used with most common flow cytometers. To demonstrate its utility, we characterized the photoswitching kinetics of Dronpa proteins in vivo and in real time. This protocol can be adapted to almost all optically controlled substances and substantially expands the set of possible experiments. More importantly, it will greatly simplify the discovery and development of new optogenetic tools.

Using the LED Thermo Flow with a Flow Cytometer
The functional core of the device is a cylindrical chamber in which LED lights are arranged in a circular manner pointing inward. This chamber can be connected to a water supply and pump, which allows for controlling the temperature of the LEDs, as well as the cell sample. The LEDs are connected to a transformer and hence the light intensity for each wavelength can be individually co...

Watch this Scientific Journal Video about LED Thermo Flow Ã¢â‚¬â€ Combining Optogenetics with Flow Cytometry at JoVE.com

LED Thermo Flow ÃƒÆ’Ã‚Â¢ÃƒÂ¢Ã¢â‚¬Å¡Ã‚Â¬ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â Combining Optogenetics with Flow Cytometry

Optically controlled substances are powerful tools to study signaling pathways. To expand the spectrum of possible experiments, we developed a device for studying optically controlled substances in real time using flow cytometry: the LED Thermo Flow.

LED Thermo Flow &#8212; Combining Optogenetics with Flow Cytometry

Optogenetic tools allow isolated, functional investigations of almost any signaling molecule within complex signaling pathways. A major obstacle is the ...

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