Name: rapid encapsulation of reconstituted cytoskeleton inside giant unilamellar vesicles
Uploaded: 2021-11-10T13:00:00
Description: Watch this Scientific Journal Video about Rapid Encapsulation of Reconstituted Cytoskeleton Inside Giant Unilamellar Vesicles at JoVE.com

APL acknowledges support by a Humboldt Research Fellowship for Experienced Researchers and from the National Science Foundation (1939310 and 1817909) and National Institutes of Health (R01 EB030031).

1. Preparation of oil-lipid-mixture
NOTE: The step needs to be performed in a fume hood following all the safety guidelines for handling chloroform.
<ol>
	<li>Take 0.5 mL of chloroform in a 15 mL glass vial. Add 88 &#181;L of 25 mg/mL dioleoyl-phosphocholine (DOPC), 9.3 &#181;L of 50 mg/mL cholesterol, and 5 &#181;L of 1 mg/mL dioleoyl-phosphoethanolamine-lissamine rhodamine B (rhodamine PE) (see Table of Materials) into the 15 ml glass vial. 
	NOTE: Th...

<ol>
	<li>Groaz, 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=Engineering+spatiotemporal+organization+and+dynamics+in+synthetic+cells.">Engineering spatiotemporal organization and dynamics in synthetic cells.</a> Wiley Interdisciplinary Reviews: Nanomedicine and Nanobiotechnology. 13 (3), 1685 (2021).</li><li>Diltemiz, S. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+artificial+cells+as+drug+carriers.">Use of artificial cells as drug carriers.</a> Materials Chemistry Frontiers. 5, 6672-6692 (2021).</li><li>Liu, A. P., Fletcher, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biology+under+construction:+In+vitro+reconstitution+of+cellular+function.">Biology under construction: In vitro reconstitution of cellular function.</a> Nature Reviews Molecular Cell Biology. 10 (9), 644-650 (2009).</li><li>Ganzinger, K. A., Schwille, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=More+from+less+-+bottom-up+reconstitution+of+cell+biology.">More from less - bottom-up reconstitution of cell biology.</a> Journal of Cell Science. 132 (4), 227488 (2019).</li><li>Bashirzadeh, Y., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Encapsulation+of+the+cytoskeleton:+Towards+mimicking+the+mechanics+of+a+cell.">Encapsulation of the cytoskeleton: Towards mimicking the mechanics of a cell.</a> Soft Matter. 15 (42), 8425-8436 (2019).</li><li>Blanchoin, L., Boujemaa-Paterski, R., Sykes, C., Plastino, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actin+dynamics,+architecture,+and+mechanics+in+cell+motility.">Actin dynamics, architecture, and mechanics in cell motility.</a> Physiol reviews. 94 (1), 235-263 (2014).</li><li>Angelova, M. I., Dimitrov, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liposome+electroformation.">Liposome electroformation.</a> Faraday Discussions of the Chemical Society. 81, 303-311 (1986).</li><li>Tsumoto, K., Matsuo, H., Tomita, M., Yoshimura, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+formation+of+giant+liposomes+through+the+gentle+hydration+of+phosphatidylcholine+films+doped+with+sugar.">Efficient formation of giant liposomes through the gentle hydration of phosphatidylcholine films doped with sugar.</a> Colloids and Surfaces B: Biointerfaces. 68 (1), 98-105 (2009).</li><li>Bailey, A. L., Cullis, P. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane+fusion+with+cationic+liposomes:+Effects+of+target+membrane+lipid+composition.">Membrane fusion with cationic liposomes: Effects of target membrane lipid composition.</a> Biochemistry. 36 (7), 1628-1634 (1997).</li><li>Haluska, C. K., Riske, K. A., Marchi-Artzner, V., Lehn, J. M., Lipowsky, R., Dimova, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time+scales+of+membrane+fusion+revealed+by+direct+imaging+of+vesicle+fusion+with+high+temporal+resolution.">Time scales of membrane fusion revealed by direct imaging of vesicle fusion with high temporal resolution.</a> Proceedings of the National Academy of Sciences. 103 (43), 15841-15846 (2006).</li><li>Nishimura, K., Suzuki, H., Toyota, T., Yomo, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Size+control+of+giant+unilamellar+vesicles+prepared+from+inverted+emulsion+droplets.">Size control of giant unilamellar vesicles prepared from inverted emulsion droplets.</a> Journal of Colloid and Interface Science. 376 (1), 119-125 (2012).</li><li>Pautot, S., Frisken, B. J., Weitz, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+unilamellar+vesicles+using+an+inverted+emulsion.">Production of unilamellar vesicles using an inverted emulsion.</a> Langmuir. 19 (7), 2870-2879 (2003).</li><li>Stachowiak, J. C., Richmond, D. L., Li, T. H., Liu, A. P., Parekh, S. H., Fletcher, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unilamellar+vesicle+formation+and+encapsulation+by+microfluidic+jetting.">Unilamellar vesicle formation and encapsulation by microfluidic jetting.</a> Proceedings of the National Academy of Sciences. 105 (12), 4697-4702 (2008).</li><li>Noireaux, V., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+new+age+of+cell-free+biology.">The new age of cell-free biology.</a> Annual Review of Biomedical Engineering. 22, 51-77 (2020).</li><li>Ho, K. K. Y., Murray, V. L., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+artificial+cells+by+combining+HeLa-based+cell-free+expression+and+ultrathin+double+emulsion+template.">Engineering artificial cells by combining HeLa-based cell-free expression and ultrathin double emulsion template.</a> Methods in Cell Biology. , 303-318 (2015).</li><li>Akashi, K., Miyata, H., Itoh, H., Kinosita, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+giant+liposomes+in+physiological+conditions+and+their+characterization+under+an+optical+microscope.">Preparation of giant liposomes in physiological conditions and their characterization under an optical microscope.</a> Biophysical Journal. 71 (6), 3242-3250 (1996).</li><li>M&#233;l&#233;ard, P., Bagatolli, L. A., Pott, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Giant+unilamellar+vesicle+electroformation:+From+lipid+mixtures+to+native+membranes+under+physiological+conditions.">Giant unilamellar vesicle electroformation: From lipid mixtures to native membranes under physiological conditions.</a> Methods in Enzymology. 465, 161-176 (2009).</li><li>Walde, P., Cosentino, K., Engel, H., Stano, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Giant+vesicles:+Preparations+and+applications.">Giant vesicles: Preparations and applications.</a> ChemBioChem. 11 (7), 848-865 (2010).</li><li>P&#233;cheur, E. I., Martin, I., Ruysschaert, J. M., Bienven&#252;e, A., Hoekstra, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane+fusion+induced+by+11-mer+anionic+and+cationic+peptides:+A+structure&#8722;+function+study.">Membrane fusion induced by 11-mer anionic and cationic peptides: A structure&#8722; function study.</a> Biochemistry. 37 (8), 2361-2371 (1998).</li><li>Morigaki, K., Walde, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Giant+vesicle+formation+from+oleic+acid/sodium+oleate+on+glass+surfaces+induced+by+adsorbed+hydrocarbon+molecules.">Giant vesicle formation from oleic acid/sodium oleate on glass surfaces induced by adsorbed hydrocarbon molecules.</a> Langmuir. 18 (26), 10509-10511 (2002).</li><li>Majumder, S., Wubshet, N., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Encapsulation+of+complex+solutions+using+droplet+microfluidics+towards+the+synthesis+of+artificial+cells.">Encapsulation of complex solutions using droplet microfluidics towards the synthesis of artificial cells.</a> Journal of Micromechanics and Microengineering. 29 (8), 83001 (2019).</li><li>Abkarian, M., Loiseau, E., Massiera, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+droplet+interface+crossing+encapsulation+(cDICE)+for+high+throughput+monodisperse+vesicle+design.">Continuous droplet interface crossing encapsulation (cDICE) for high throughput monodisperse vesicle design.</a> Soft Matter. 7 (10), 4610-4614 (2011).</li><li>Van de Cauter, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optimized+cDICE+for+efficient+reconstitution+of+biological+systems+in+giant+unilamellar+vesicles.">Optimized cDICE for efficient reconstitution of biological systems in giant unilamellar vesicles.</a> ACS Synthetic Biology. 10 (7), 1690-1702 (2021).</li><li>Claudet, C., In, M., Massiera, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+to+disperse+lipids+as+aggregates+in+oil+for+bilayers+production.">Method to disperse lipids as aggregates in oil for bilayers production.</a> The European Physical Journal E. 39 (1), 1-6 (2016).</li><li>Bashirzadeh, Y., Wubshet, N. H., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Confinement+Geometry+tunes+fascin-actin+bundle+structures+and+consequently+the+shape+of+a+lipid+bilayer+vesicle.">Confinement Geometry tunes fascin-actin bundle structures and consequently the shape of a lipid bilayer vesicle.</a> Frontiers in Molecular Biosciences. 7, 610277 (2020).</li><li>Bashirzadeh, Y., 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=Actin+crosslinker+competition+and+sorting+drive+emergent+GUV+size-dependent+actin+network+architecture.">Actin crosslinker competition and sorting drive emergent GUV size-dependent actin network architecture.</a> Communications Biology. 4, 1136 (2021).</li><li>Bashirzadeh, Y., Moghimianavval, H., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Encapsulated+actomyosin+patterns+drive+cell-like+membrane+shape+changes.">Encapsulated actomyosin patterns drive cell-like membrane shape changes.</a> bioRxiv. , (2021).</li><li>Litschel, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstitution+of+contractile+actomyosin+rings+in+vesicles.">Reconstitution of contractile actomyosin rings in vesicles.</a> Nature Communications. 12 (1), 1-10 (2021).</li><li>Vitale, S. A., Katz, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liquid+droplet+dispersions+formed+by+homogeneous+liquid&#8722;+liquid+nucleation:&amp;#34;The+Ouzo+effect.&amp;#34.">Liquid droplet dispersions formed by homogeneous liquid&#8722; liquid nucleation:&amp;#34;The Ouzo effect.&amp;#34.</a> Langmuir. 19 (10), 4105-4110 (2003).</li><li>Pautot, S., Frisken, B. J., Weitz, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+asymmetric+vesicles.">Engineering asymmetric vesicles.</a> Proceedings of the National Academy of Sciences. 100 (19), 10718-10721 (2003).</li><li>Deshpande, S., Dekker, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On-chip+microfluidic+production+of+cell-sized+liposomes.">On-chip microfluidic production of cell-sized liposomes.</a> Nature Protocols. 13 (5), 856-874 (2018).</li><li>Deshpande, S., Caspi, Y., Meijering, A. E. C., Dekker, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Octanol-assisted+liposome+assembly+on+chip.">Octanol-assisted liposome assembly on chip.</a> Nature Communications. 7, 10447 (2016).</li><li>Wubshet, N. H., Bashirzadeh, Y., Liu, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fascin-induced+actin+protrusions+are+suppressed+by+dendritic+networks+in+GUVs.">Fascin-induced actin protrusions are suppressed by dendritic networks in GUVs.</a> Molecular Biology of the Cell. 32 (18), 1634-1640 (2021).</li></ol>

Different methods of generating GUVs have been explored for the creation of synthetic cells&#160;However, the complexity of the procedures, extended time to attain encapsulation, restriction of lipid types and molecular composition of the encapsulant, need for non-physiological chemicals to facilitate encapsulation, low GUV yield, and inconsistencies in encapsulation efficiency have continued to challenge researchers in this field. Considering the wide range of potential studies that can be embarked in bottom-up syntheti...

Lipid bilayer compartments are used as model synthetic cells for studying enclosed organic reactions and membrane-based processes or as carrier modules in drug delivery applications1,2. Bottom-up biology with purified components requires minimal experimental systems to explore properties and interactions between biomolecules, such as proteins and lipids3,4. However, with the advancement of the field, there is an increased need for more complex experimental systems that better imitate the conditions in biological cells. Encapsulation in GUVs is a practical approach that can offer some of these cell-like properties by providing a deformable and selectively permeable lipid bilayer and a confined reaction space. In particular, in vitro reconstitution of cytoskeletal systems, as models of synthetic cells, can benefit from encapsulation in membrane compartments5. Many cytoskeletal proteins bind and interact with the cell membrane. As most cytoskeletal assemblies form structures that span the entirety of the cell, their shape is naturally determined by cell-sized confinement6.
Different methods are used to generate GUVs, such as the swelling7,8, small vesicle fusion9,10, emulsion transfer11,12, pulsed jetting13, and other microfluidic approaches14,15. Although these methods are still utilized, each has its limitations. Thus, a robust and straightforward approach with a high yield of GUV encapsulation is highly desirable. Although techniques such as spontaneous swelling and electroswelling are widely adopted for the formation of GUVs, these methods are primarily compatible with specific lipid compositions16, low salt concentration buffers17, smaller encapsulant molecular size18, and require a high volume of the encapsulant. Fusing multiple small vesicles into a GUV is inherently energetically unfavorable, thus requiring specificity in charged lipid compositions9 and/or external fusion-inducing agents, such as peptides19&#160;or other chemicals. Emulsion transfer and microfluidic methods, on the other hand, may require droplet stabilization through surfactant and solvent removal after bilayer formation, respectively18,20. The complexity of experimental setup and device in microfluidic techniques such as pulsed jetting impose an additional challenge21. cDICE is an emulsion-based method derived from similar principles governing emulsion transfer22,23. An aqueous solution (outer solution) and a lipid-oil mixture are stratified by centrifugal forces in a rotating cylindrical chamber (cDICE chamber) forming a lipid saturated interface. Shuttling lipid monolayered aqueous droplets into the rotating cDICE chamber results in zipping of a bilayer as droplets cross the lipid-saturated interface into the outer aqueous solution22,24. The cDICE approach is a robust technique for GUV encapsulation. With the presented modified method, not only the high vesicle yield typical for cDICE with a significantly shorter encapsulation time (a few seconds) is achieved but GUV generation time that allow for the observation of time-dependent processes (e.g., actin cytoskeletal network formation) is significantly reduced. The protocol takes about 15-20 min from the start to GUV collection and imaging. Here, GUV generation is described using the modified cDICE method for encapsulating actin and actin-binding proteins (ABPs). However, the presented technique is applicable for encapsulating a wide range of biological reactions and membrane interactions, from the assembly of biopolymers to cell-free protein expression to membrane fusion-based cargo transfer.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>18:1 Liss Rhod PE lipid in chloroform</td>
			<td>Avanti Polar Lipids</td>
			<td>810150C</td>
			<td></td>
		</tr>
		<tr>
			<td>96 Well Optical Btm Pit PolymerBase</td>
			<td>ThermoFisher Scientific</td>
			<td>165305</td>
			<td></td>
		</tr>
		<tr>
			<td>Actin from rabbit skeletal muscle</td>
			<td>Cytoskeleton</td>
			<td>AKL99-A</td>
			<td></td>
		</tr>
		<tr>
			<td>ATTO 488-actin from rabbit skeletal muscle</td>
			<td>Hypermol</td>
			<td>8153-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Axygen microtubes (200 &#181;L)</td>
			<td>Fisher Scientific</td>
			<td>14-222-262</td>
			<td>for handling ABPs</td>
		</tr>
		<tr>
			<td>Black resin</td>
			<td>Formlabs</td>
			<td>RS-F2-GPBK-04</td>
			<td></td>
		</tr>
		<tr>
			<td>Cholesterol (powder)</td>
			<td>Avanti Polar Lipids</td>
			<td>700100P</td>
			<td></td>
		</tr>
		<tr>
			<td>Choloroform</td>
			<td>Sigma Aldrich</td>
			<td>67-66-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Clear resin</td>
			<td>Formlabs</td>
			<td>RS-F2-GPCL-04</td>
			<td></td>
		</tr>
		<tr>
			<td>CSU-X1 Confocal Scanner Unit</td>
			<td>YOKOGAWA</td>
			<td>CSU-X1</td>
			<td></td>
		</tr>
		<tr>
			<td>Density gradient medium (Optiprep)</td>
			<td>Sigma-Aldrich</td>
			<td>D1556</td>
			<td></td>
		</tr>
		<tr>
			<td>DOPC lipid in chloroform</td>
			<td>Avanti Polar Lipids</td>
			<td>850375C</td>
			<td></td>
		</tr>
		<tr>
			<td>Fascin</td>
			<td>homemade</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>F-buffer</td>
			<td>homemade</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Fisherbrand microtubes (1.5 mL)</td>
			<td>Fisher Scientific</td>
			<td>05-408-129</td>
			<td></td>
		</tr>
		<tr>
			<td>FS02 Sonicator</td>
			<td>Fischer Scientific</td>
			<td>FS20</td>
			<td></td>
		</tr>
		<tr>
			<td>G-buffer</td>
			<td>homemade</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>158968</td>
			<td></td>
		</tr>
		<tr>
			<td>iXon X3 camera</td>
			<td>Andor</td>
			<td>DU-897E-CS0</td>
			<td></td>
		</tr>
		<tr>
			<td>Mineral oil</td>
			<td>Acros Organics</td>
			<td>8042-47-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Olympus IX81 Inverted Microscope</td>
			<td>Olympus</td>
			<td>IX21</td>
			<td></td>
		</tr>
		<tr>
			<td>Olympus PlanApo N 60x Oil Microscope Objective</td>
			<td>Olumpus</td>
			<td>1-U2B933</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone oil</td>
			<td>Sigma-Aldrich</td>
			<td>317667</td>
			<td></td>
		</tr>
	</tbody>
</table>

rapid encapsulation of reconstituted cytoskeleton inside giant unilamellar vesicles

Giant unilamellar vesicles (GUVs) are frequently used as models of biological membranes and thus are a great tool to study membrane-related cellular processes in vitro. In recent years, encapsulation within GUVs has proven to be a helpful approach for reconstitution experiments in cell biology and related fields. It better mimics confinement conditions inside living cells, as opposed to conventional biochemical reconstitution. Methods for encapsulation inside GUVs are often not easy to implement, and success rates can differ significantly from lab to lab. One technique that has proven to be successful for encapsulating more complex protein systems is called continuous droplet interface crossing encapsulation (cDICE). Here, a cDICE-based method is presented for rapidly encapsulating cytoskeletal proteins in GUVs with high encapsulation efficiency. In this method, first, lipid-monolayer droplets are generated by emulsifying a protein solution of interest in a lipid/oil mixture. After being added into a rotating 3D-printed chamber, these lipid-monolayered droplets then pass through a second lipid monolayer at a water/oil interface inside the chamber to form GUVs that contain the protein system. This method simplifies the overall procedure of encapsulation within GUVs and speeds up the process, and thus allows us to confine and observe the dynamic evolution of network assembly inside lipid bilayer vesicles. This platform is handy for studying the mechanics of cytoskeleton-membrane interactions in confinement.

To demonstrate the successful generation of cytoskeletal GUVs using the current protocol, fascin-actin bundle structures in GUVs were reconstituted. Fascin is a short crosslinker of actin filaments which forms stiff parallel-aligned actin bundles and is purified from E. coli as Glutathione-S-Transferase (GST) fusion protein26. 5 &#181;M of actin was first reconstituted, including 0.53 &#181;M of ATTO488 actin in the actin polymerization buffer and 7.5% of the density gradient medium. Upon...

Watch this Scientific Journal Video about Rapid Encapsulation of Reconstituted Cytoskeleton Inside Giant Unilamellar Vesicles at JoVE.com

Rapid Encapsulation of Reconstituted Cytoskeleton Inside Giant Unilamellar Vesicles

This article introduces a simple method for expeditious production of giant unilamellar vesicles with encapsulated cytoskeletal proteins. The method proves to be useful for bottom-up reconstitution of cytoskeletal structures in confinement and cytoskeleton-membrane interactions.

Giant unilamellar vesicles (GUVs) are frequently used as models of biological membranes and thus are a great tool to study membrane-related cellular ...

In recent years, encapsulation within cell-sized lipid bilayer vesicles has proven to be a useful method for in vitro reconstitution experiments. The method we present will greatly help with cytoskeleton reconstitution in synthetic cell research. With this method, we can generate heterogeneously sized giant unilamellar vesicles with a high yield.The vesicle generation time is significantly decreased compared to the conventional cDICE technique. We can encapsulate cell-free transcription-translation systems isolated from complex, simultaneously occurring cellular processes to examine molecular pathways. This method can be utilized to assemble minimal protocells towards creating functional synthetic cells.Start preparing an oil-lipid mixture by transferring dioleoyl-phosphocholine, cholesterol, and rhodamine PE to a 15-milliliter glass vial. Then, add 0.5 milliliters of chloroform in the vial. Pipette 7.2 milliliters of silicone oil and 1.8 milliliters of mineral oil in a separate 15-milliliter tube and mix the oils by vortexing at a speed of 3, 200 rotations per minute for 10 seconds.Then, add the oil mixture to the vial containing the lipid and chloroform mixture and vortex the mixture at the speed of 3, 200 rotations per minute for 10 to 15 seconds until the resulting lipids-in-oil mix is slightly cloudy, as the lipids are not fully dissolved in the oil. Next, sonicate the lipid in oil dispersion in a bath sonicator with ultrasonic power of 80 watts and an operating frequency of 40 kilohertz for 30 minutes at room temperature. If not used immediately, store the lipid-oil mixture at four degrees Celsius for 24 hours.To generate the vesicles, use the assembly with a 3D-printed shaft made from black resin mounted on the benchtop stir plate at the speed of 1, 200 rotations per minute. Then, mount the 3D-printed continuous droplet interface crossing encapsulation, or cDICE chamber, made from the clear resin on the black resin shaft. Prepare 1-to 10-micromolar actin solution in globular actin buffer, or G buffer, including 10%ATO 488 actin.To begin the actin polymerization, add filamentous actin polymerization buffer, or F buffer, in actin solution on ice and then keep the solutions on ice to slow down actin polymerization before adding a crosslinker. To prepare the actin binding proteins, or ABPs, from 1.75 milligrams per milliliter of fascin stock, aliquot 1.57 microliters of fascin in a separate microtube. Next, add 7.5%of density gradient medium into the actin solution to create a density gradient between the outer and the inner aqueous phase and facilitate giant unilamellar vesicles or GUVs, sedimentation.Then, dispense 700 microliters of 200-millimolar glucose as the outer solution into the chamber. Add enough lipid-oil mixture into the chamber until 60%to 80%of the chamber is filled. An interface will be formed between the lipid-oil mixture and the outer solution.Prepare an actin-ABP mixture by transferring ABPs into the actin solution. Then, use a regular 100-to 1, 000-microliter pipette to transfer the 700 microliters of the lipid-oil mixture into the actin-ABP mixture. Pipette up and down eight times to generate cell-sized lipid monolayer emulsion droplets with a diameter of 7 to 100 microns.Use the same 100-to 1, 000-microliter pipette to dispense the entire emulsion into the rotating chamber. The droplets will acquire a second leaflet of lipids by crossing the lipid monolayer at the oil-outer solution interface, thereby forming GUVs. When done, remove the chamber from the stir plate and discard most of the lipid-oil mixture by tilting the chamber in the waste container.By holding the chamber with its lid facing inside, open the chamber lid and slightly tilt the chamber inwards. The interface between the outer solution containing GUVs and the lipid-oil mixture will be visible from the chamber opening where the lid is located. Use a pipette to collect enough outer solution containing GUVs and dispense 50 to 300 microliters of the outer solution into a 96-well plate to obtain an appropriate density of GUVs.For imaging the GUVs, set up the 96-well plate on the stage of an inverted microscope equipped with an oil immersion 60X objective lens. Open an image sequence of interest in an image processing software, ImageJ Fiji, and identify the image with the highest intensity. Hold Control Shift C to open the brightness and contrast window and click on the reset tab.In the ImageJ Fiji menu, go to the Analyze and Set Scale tabs to enter the known physical distance and unit for each image pixel. Once done, go to the Image, Stacks, and then 3D Project buttons to reconstruct a 3D image from the Z stack. Set the Projection method as Brightness Point, Slice spacing as 0.5 micrometers, and then check mark the Interpolate box.Use the default options for the rest of the settings and capture images. The representative image shows a confocal image of rhodamine PE-labeled GUVs with encapsulated fascin-actin bundles. Transferring the actin binding proteins into the actin solution, then adding lipid-oil mixture and generation of lipid monolayer droplets should take place in a few seconds to avoid the formation of actin networks before the encapsulation.We have used this modified cDICE technique to examine the roles of different actin net cross-linkers in organizing actin networks. We expect this method will help other researchers to explore the regulation of other cytoskeleton proteins.

rapid-encapsulation-reconstituted-cytoskeleton-inside-giant

Research

JoVE Journal

Bioengineering

High Throughput Single-cell and Multiple-cell Micro-encapsulation

Microfluidic encapsulation methods have been previously utilized to capture cells in picoliter-scale aqueous, monodisperse drops, providing confinement from a bulk fluid environment with applications in high throughput screening, cytometry, and mass spectrometry. We describe a method to not only encapsulate single cells, but to repeatedly capture a set number of cells (here we demonstrate one- and two-cell encapsulation) to study both isolation and the interactions between cells in groups of controlled sizes. By combining drop generation techniques with cell and particle ordering, we demonstrate controlled encapsulation of cell-sized particles for efficient, continuous encapsulation. Using an aqueous particle suspension and immiscible fluorocarbon oil, we generate aqueous drops in oil with a flow focusing nozzle. The aqueous flow rate is sufficiently high to create ordering of particles which reach the nozzle at integer multiple frequencies of the drop generation frequency, encapsulating a controlled number of cells in each drop. For representative results, 9.9 &mu;m polystyrene particles are used as cell surrogates. This study shows a single-particle encapsulation efficiency Pk=1 of 83.7% and a double-particle encapsulation efficiency Pk=2 of 79.5% as compared to their respective Poisson efficiencies of 39.3% and 33.3%, respectively. The effect of consistent cell and particle concentration is demonstrated to be of major importance for efficient encapsulation, and dripping to jetting transitions are also addressed. 
Introduction 
Continuous media aqueous cell suspensions share a common fluid environment which allows cells to interact in parallel and also homogenizes the effects of specific cells in measurements from the media. High-throughput encapsulation of cells into picoliter-scale drops confines the samples to protect drops from cross-contamination, enable a measure of cellular diversity within samples, prevent dilution of reagents and expressed biomarkers, and amplify signals from bioreactor products. Drops also provide the ability to re-merge drops into larger aqueous samples or with other drops for intercellular signaling studies.1,2 The reduction in dilution implies stronger detection signals for higher accuracy measurements as well as the ability to reduce potentially costly sample and reagent volumes.3 Encapsulation of cells in drops has been utilized to improve detection of protein expression,4 antibodies,5,6 enzymes,7 and metabolic activity8 for high throughput screening, and could be used to improve high throughput cytometry.9 Additional studies present applications in bio-electrospraying of cell containing drops for mass spectrometry10 and targeted surface cell coatings.11 Some applications, however, have been limited by the lack of ability to control the number of cells encapsulated in drops. Here we present a method of ordered encapsulation12 which increases the demonstrated encapsulation efficiencies for one and two cells and may be extrapolated for encapsulation of a larger number of cells.
To achieve monodisperse drop generation, microfluidic "flow focusing" enables the creation of controllable-size drops of one fluid (an aqueous cell mixture) within another (a continuous oil phase) by using a nozzle at which the streams converge.13 For a given nozzle geometry, the drop generation frequency f and drop size can be altered by adjusting oil and aqueous flow rates Qoil and Qaq. As the flow rates increase, the flows may transition from drop generation to unstable jetting of aqueous fluid from the nozzle.14 
When the aqueous solution contains suspended particles, particles become encapsulated and isolated from one another at the nozzle. For drop generation using a randomly distributed aqueous cell suspension, the average fraction of drops Dk containing k cells is dictated by Poisson statistics, where Dk = &lambda;k exp(-&lambda;)/(k!) and &lambda; is the average number of cells per drop. The fraction of cells which end up in the "correctly" encapsulated drops is calculated using Pk = (k x Dk)/&Sigma;(k' x Dk'). The subtle difference between the two metrics is that Dk relates to the utilization of aqueous fluid and the amount of drop sorting that must be completed following encapsulation, and Pk relates to the utilization of the cell sample. As an example, one could use a dilute cell suspension (low &lambda;) to encapsulate drops where most drops containing cells would contain just one cell. While the efficiency metric Pk would be high, the majority of drops would be empty (low Dk), thus requiring a sorting mechanism to remove empty drops, also reducing throughput.15
Combining drop generation with inertial ordering provides the ability to encapsulate drops with more predictable numbers of cells per drop and higher throughputs than random encapsulation. Inertial focusing was first discovered by Segre and Silberberg16 and refers to the tendency of finite-sized particles to migrate to lateral equilibrium positions in channel flow. Inertial ordering refers to the tendency of the particles and cells to passively organize into equally spaced, staggered, constant velocity trains. Both focusing and ordering require sufficiently high flow rates (high Reynolds number) and particle sizes (high Particle Reynolds number).17,18 Here, the Reynolds number Re =uDh/&nu; and particle Reynolds number Rep =Re(a/Dh)2, where u is a characteristic flow velocity, Dh [=2wh/(w+h)] is the hydraulic diameter, &nu; is the kinematic viscosity, a is the particle diameter, w is the channel width, and h is the channel height. Empirically, the length required to achieve fully ordered trains decreases as Re and Rep increase. Note that the high Re and Rep requirements (for this study on the order of 5 and 0.5, respectively) may conflict with the need to keep aqueous flow rates low to avoid jetting at the drop generation nozzle. Additionally, high flow rates lead to higher shear stresses on cells, which are not addressed in this protocol. The previous ordered encapsulation study demonstrated that over 90% of singly encapsulated HL60 cells under similar flow conditions to those in this study maintained cell membrane integrity.12 However, the effect of the magnitude and time scales of shear stresses will need to be carefully considered when extrapolating to different cell types and flow parameters. The overlapping of the cell ordering, drop generation, and cell viability aqueous flow rate constraints provides an ideal operational regime for controlled encapsulation of single and multiple cells.
Because very few studies address inter-particle train spacing,19,20 determining the spacing is most easily done empirically and will depend on channel geometry, flow rate, particle size, and particle concentration. Nonetheless, the equal lateral spacing between trains implies that cells arrive at predictable, consistent time intervals. When drop generation occurs at the same rate at which ordered cells arrive at the nozzle, the cells become encapsulated within the drop in a controlled manner. This technique has been utilized to encapsulate single cells with throughputs on the order of 15 kHz,12 a significant improvement over previous studies reporting encapsulation rates on the order of 60-160 Hz.4,15 In the controlled encapsulation work, over 80% of drops contained one and only one cell, a significant efficiency improvement over Poisson (random) statistics, which predicts less than 40% efficiency on average.12
In previous controlled encapsulation work,12 the average number of particles per drop &lambda; was tuned to provide single-cell encapsulation. We hypothesize that through tuning of flow rates, we can efficiently encapsulate any number of cells per drop when &lambda; is equal or close to the number of desired cells per drop. While single-cell encapsulation is valuable in determining individual cell responses from stimuli, multiple-cell encapsulation provides information relating to the interaction of controlled numbers and types of cells. Here we present a protocol, representative results using polystyrene microspheres, and discussion for controlled encapsulation of multiple cells using a passive inertial ordering channel and drop generation nozzle.

Combining monodisperse drop generation with inertial ordering of cells and particles, we describe a method to encapsulate a desired number of cells or particles in a single drop at kHz rates. We demonstrate efficiencies twice exceeding those of unordered encapsulation for single- and double-particle drops.

Microfluidic encapsulation methods have been previously utilized to capture cells in picoliter-scale aqueous, monodisperse drops, providing confinement ...

The Encapsulation of Cell-free Transcription and Translation Machinery in Vesicles for the Construction of Cellular Mimics

As interest shifts from individual molecules to systems of molecules, an increasing number of laboratories have sought to build from the bottom up cellular mimics that better represent the complexity of cellular life. To date there are a number of paths that could be taken to build compartmentalized cellular mimics, including the exploitation of water-in-oil emulsions, microfluidic devices, and vesicles. Each of the available options has specific advantages and disadvantages. For example, water-in-oil emulsions give high encapsulation efficiency but do not mimic well the permeability barrier of living cells. The primary advantage of the methods described herein is that they are all easy and cheap to implement. Transcription-translation machinery is encapsulated inside of phospholipid vesicles through a process that exploits common instrumentation, such as a centrifugal evaporator and an extruder. Reactions are monitored by fluorescence spectroscopy. The protocols can be adapted for recombinant protein expression, the construction of cellular mimics, the exploration of the minimum requirements for cellular life, or the assembly of genetic circuitry.

Herein we describe simple methods for the preparation of vesicles, the encapsulation of transcription and translation machinery, and the monitoring of protein production. The resulting cell-free systems can be used as a starting point from which to build increasingly complex cellular mimics.

As interest shifts from individual molecules to systems of molecules, an increasing number of laboratories have sought to build from the bottom up ...

Forming Giant-sized Polymersomes Using Gel-assisted Rehydration

Polymer vesicles, or polymersomes, are being widely explored as synthetic analogs of lipid vesicles based on their stability, robustness, barrier properties, chemical versatility and tunable physical characteristics. Typical methods used to prepare giant-sized (&gt; 4 &#181;m) vesicles, however, are both time and labor intensive, yielding low numbers of intact polymersomes. Here, we present for the first time the use of gel-assisted rehydration for the rapid and high-yielding formation of giant (&gt;4 &#181;m) polymer vesicles (polymersomes). Using this method, polymersomes can be formed from a wide array of rehydration solutions including several different physiologically-compatible buffers and full cell culture media, making them readily useful for biomimicry studies. This technique is also capable of reliably producing polymersomes from different polymer compositions with far better yields and much less difficulty than traditional methods. Polymersome size is readily tunable by altering temperature during rehydration or adding membrane fluidizers to the polymer membrane, generating giant-sized polymersomes (&gt;100 &#181;m).

We present a protocol to rapidly form giant polymer vesicles (pGVs). Briefly, polymer solutions are dehydrated on dried agarose films adhered to coverslips. Rehydration of the polymer films results in rapid formation of pGVs. This method greatly advances the preparation of synthetic giant vesicles for direct applications in biomimetic studies.

Polymer vesicles, or polymersomes, are being widely explored as synthetic analogs of lipid vesicles based on their stability, robustness, barrier ...

Preparation and Characterization of Novel HDL-mimicking Nanoparticles for Nerve Growth Factor Encapsulation

The objective of this article is to introduce preparation and characterization methods for nerve growth factor (NGF)-loaded, high-density, lipoprotein (HDL)-mimicking nanoparticles (NPs). HDLs are endogenous NPs and have been explored as vehicles for the delivery of therapeutic agents. Various methods have been developed to prepare HDL-mimicking NPs. However, they are generally complicated, time consuming, and difficult for industrial scale-up. In this study, one-step homogenization was used to mix the excipients and form the prototype NPs. NGF is a water-soluble protein of 26 kDa. To facilitate the encapsulation of NGF into the lipid environment of HDL-mimicking NPs, protamine USP was used to form an ion-pair complex with NGF to neutralize the charges on the NGF surface. The NGF/protamine complex was then introduced into the prototype NPs. Apolipoprotein A-I was finally coated on the surface of the NPs. NGF HDL-mimicking NPs showed preferable properties in terms of particle size, size distribution, entrapment efficiency, in vitro release, bioactivity, and biodistribution. With the careful design and exploration of homogenization in HDL-mimicking NPs, the procedure was greatly simplified, and the NPs were made scalable. Moreover, various challenges, such as separating unloaded NGF from the NPs, conducting reliable in vitro release studies, and measuring the bioactivity of the NPs, were overcome.

Simple homogenization was used to prepare novel, high-density, lipoprotein-mimicking nanoparticles to encapsulate nerve growth factor. Challenges, detailed protocols for nanoparticle preparation, in vitro characterization, and in vivo studies are described in this article.

The objective of this article is to introduce preparation and characterization methods for nerve growth factor (NGF)-loaded, high-density, lipoprotein ...

Decellularization of Whole Human Heart Inside a Pressurized Pouch in an Inverted Orientation

The ultimate solution for patients with end-stage heart failure is organ transplant. But donor hearts are limited, immunosuppression is required, and ultimately rejection can occur. Creating a functional, autologous bio-artificial heart could solve these challenges. Biofabrication of a heart comprised of scaffold and cells is one option. A natural scaffold with tissue-specific composition as well as micro- and macro-architecture can be obtained by decellularizing hearts from humans or large animals such as pigs. Decellularization involves washing out cellular debris while preserving 3D extracellular matrix and vasculature and allowing &#34;cellularization&#34; at a later timepoint. Capitalizing on our novel finding that perfusion decellularization of complex organs is possible, we developed a more &#34;physiological&#34; method to decellularize non-transplantable human hearts by placing them inside a pressurized pouch, in an inverted orientation, under controlled pressure. The purpose of using a pressurized pouch is to create pressure gradients across the aortic valve to keep it closed and improve myocardial perfusion. Simultaneous assessment of flow dynamics and cellular debris removal during decellularization allowed us to monitor both fluid inflow and debris outflow, thereby generating a scaffold that can be used either for simple cardiac repair (e.g. as a patch or valve scaffold) or as a whole-organ scaffold.

This method enables decellularization of a complex solid organ using a simple protocol based on osmotic shock and perfusion of ionic detergent with minimal organ matrix disruption. It comprises a novel decellularization technique for human hearts inside a pressurized pouch with real-time monitoring of flow dynamics and cellular debris outflow.

The ultimate solution for patients with end-stage heart failure is organ transplant. But donor hearts are limited, immunosuppression is required, and ...

3D Printing of In Vitro Hydrogel Microcarriers by Alternating Viscous-Inertial Force Jetting

Microcarriers are beads with a diameter of 60-250 &#181;m and a large specific surface area, which are commonly used as carriers for large-scale cell cultures. Microcarrier culture technology has become one of the main techniques in cytological research and is commonly used in the field of large-scale cell expansion. Microcarriers have also been shown to play an increasingly important role in in vitro tissue engineering construction and clinical drug screening. Current methods for preparing microcarriers include microfluidic chips and inkjet printing, which often rely on complex flow channel design, an incompatible two-phase interface, and a fixed nozzle shape. These methods face the challenges of complex nozzle processing, inconvenient nozzle changes, and excessive extrusion forces when applied to multiple bioink. In this study, a 3D printing technique, called alternating viscous-inertial force jetting, was applied to enable the construction of hydrogel microcarriers with a diameter of 100-300 &#181;m. Cells were subsequently seeded on microcarriers to form tissue engineering modules. Compared to existing methods, this method offers a free nozzle tip diameter, flexible nozzle switching, free control of printing parameters, and mild printing conditions for a wide range of bioactive materials.

3D Printing of In Vitro Hydrogel Microcarriers by Alternating Viscous-Inertial Force Jetting

Presented here is a mild 3D printing technique driven by alternating viscous-inertial forces to enable the construction of hydrogel microcarriers. Homemade nozzles offer flexibility, allowing easy replacement for different materials and diameters. Cell binding microcarriers with a diameter of 50-500 &#181;m can be obtained and collected for further culturing.

Microcarriers are beads with a diameter of 60-250 &#181;m and a large specific surface area, which are commonly used as carriers for large-scale cell ...

Quantifying Cytoskeleton Dynamics Using Differential Dynamic Microscopy

Cells can crawl, self-heal, and tune their stiffness due to their remarkably dynamic cytoskeleton. As such, reconstituting networks of cytoskeletal biopolymers may lead to a host of active and adaptable materials. However, engineering such materials with precisely tuned properties requires measuring how the dynamics depend on the network composition and synthesis methods. Quantifying such dynamics is challenged by variations across the time, space, and formulation space of composite networks. The protocol here describes how the Fourier analysis technique, differential dynamic microscopy (DDM), can quantify the dynamics of biopolymer networks and is particularly well suited for studies of cytoskeleton networks. DDM works on time sequences of images acquired using a range of microscopy modalities, including laser-scanning confocal, widefield fluorescence, and brightfield imaging. From such image sequences, one can extract characteristic decorrelation times of density fluctuations across a span of wave vectors. A user-friendly, open-source Python package to perform DDM analysis is also developed. With this package, one can measure the dynamics of labeled cytoskeleton components or of embedded tracer particles, as demonstrated here with data of intermediate filament (vimentin) networks and active actin-microtubule networks. Users with no prior programming or image processing experience will be able to perform DDM using this software package and associated documentation.

Differential dynamic microscopy (DDM) combines features of dynamic light scattering and microscopy. Here, the process of using DDM to characterize reconstituted cytoskeleton networks by quantifying the subdiffusive and caged dynamics of particles in vimentin networks and the ballistic motion of active myosin-driven actin-microtubule composites is presented.

Cells can crawl, self-heal, and tune their stiffness due to their remarkably dynamic cytoskeleton. As such, reconstituting networks of cytoskeletal ...

In Vitro Reconstitution of the Actin Cytoskeleton Inside Giant Unilamellar Vesicles

The actin cytoskeleton, the principal mechanical machinery in the cell, mediates numerous essential physical cellular activities, including cell deformation, division, migration, and adhesion. However, studying the dynamics and structure of the actin network in vivo is complicated by the biochemical and genetic regulation within live cells. To build a minimal model devoid of intracellular biochemical regulation, actin is encapsulated inside giant unilamellar vesicles (GUVs, also called liposomes). The biomimetic liposomes are cell-sized and facilitate a quantitative insight into the mechanical and dynamical properties of the cytoskeleton network, opening a viable route for bottom-up synthetic biology. To generate liposomes for encapsulation, the inverted emulsion method (also referred to as the emulsion transfer method) is utilized, which is one of the most successful techniques for encapsulating complex solutions into liposomes to prepare various cell-mimicking systems. With this method, a mixture of proteins of interest is added to the inner buffer, which is later emulsified in a phospholipid-containing mineral oil solution to form monolayer lipid droplets. The desired liposomes are generated from monolayer lipid droplets crossing a lipid/oil-water interface. This method enables the encapsulation of concentrated actin polymers into the liposomes with desired lipid components, paving the way for in vitro reconstitution of a biomimicking cytoskeleton network.

In Vitro Reconstitution of the Actin Cytoskeleton Inside Giant Unilamellar Vesicles

In this manuscript, we demonstrate the experimental techniques to encapsulate the F-actin cytoskeleton into giant unilamellar lipid vesicles (also called liposomes), and the method to form a cortex-biomimicking F-actin layer at the inner leaflet of the liposome membrane.

The actin cytoskeleton, the principal mechanical machinery in the cell, mediates numerous essential physical cellular activities, including cell ...

Light-Controlled Reversible Protein Patterning on Lipid Membranes

Dynamic Light-Induced Protein Patterns at Model Membranes

The precise localization and activation of proteins at the cell membrane at a certain time gives rise to many cellular processes, including cell polarization, migration, and division. Thus, methods to recruit proteins to model membranes with subcellular resolution and high temporal control are essential when reproducing and controlling such processes in synthetic cells. Here, a method is described for fabricating light-regulated reversible protein patterns at lipid membranes with high spatiotemporal precision. For this purpose, we immobilize the photoswitchable protein iLID (improved light-inducible dimer) on supported lipid bilayers (SLBs) and on the outer membrane of giant unilamellar vesicles (GUVs). Upon local blue light illumination, iLID binds to its partner Nano (wild-type SspB) and allows the recruitment of any protein of interest (POI) fused to Nano from the solution to the illuminated area on the membrane. This binding is reversible in the dark, which provides dynamic binding and release of the POI. Overall, this is a flexible and versatile method for regulating the localization of proteins with high precision in space and time using blue light.

Author Spotlight: Photo Switchable Protein Recruitment for Reversible Patterning in Artificial Cellular Systems

Here, a protocol is described for generating light-regulated and reversible protein patterns with high spatiotemporal precision at artificial lipid membranes. The method consists of the localized photoactivation of the protein iLID (improved light-inducible dimer) immobilized on model membranes that, under blue light, binds to its partner protein Nano (wild-type SspB).

The precise localization and activation of proteins at the cell membrane at a certain time gives rise to many cellular processes, including cell ...

Cell-Free Expression of Membrane Proteins in Giant Unilamellar Vesicles

Reconstitution of the Bacterial Glutamate Receptor Channel by Encapsulation of a Cell-Free Expression System

Cell-free expression (CFE) systems are powerful tools in synthetic biology that allow biomimicry of cellular functions like biosensing and energy regeneration in synthetic cells. Reconstruction of a wide range of cellular processes, however, requires successful reconstitution of membrane proteins into the membrane of synthetic cells. While the expression of soluble proteins is usually successful in common CFE systems, the reconstitution of membrane proteins in lipid bilayers of synthetic cells has proven to be challenging. Here, a method for reconstitution of a model membrane protein, bacterial glutamate receptor (GluR0), in giant unilamellar vesicles (GUVs) as model synthetic cells based on encapsulation and incubation of the CFE reaction inside synthetic cells is demonstrated. Utilizing this platform, the effect of substituting the N-terminal signal peptide of GluR0 with proteorhodopsin signal peptide on successful cotranslational translocation of GluR0 into membranes of hybrid GUVs is demonstrated. This method provides a robust procedure that will allow cell-free reconstitution of various membrane proteins in synthetic cells.

Author Spotlight: Membrane Protein Reconstitution in Synthetic Cells

This protocol describes the inverted emulsion method used to encapsulate a cell-free expression (CFE) system within a giant unilamellar vesicle (GUV) for the investigation of the synthesis and incorporation of a model membrane protein into the lipid bilayer.