The authors thank S-Y Choi (Chonnam National University) for valuable comments and thorough reading of our manuscript. This work was supported by a research fund of Chungnam National University.

1. Transgene Subcloning
<ol>
	<li>Choose an appropriate restriction enzyme recognition site (or sites) in the MCS of pEUI(+), and subclone the gene of interest in the desired direction (Figure 1). 
	NOTE: The EGFP or FLAG epitope-tagged ankyrin repeat domain 13A (ANKRD13A) transgene was subcloned in EcoRI site of the pEUI(+) vector using T4 DNA polymerase in a sequence- and ligation-independent cloning method19.</li>
	<li>Linearize the pEUI(+)...

<ol>
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Biotechnol. 9 (5), 451-456 (1998).</li><li>Clackson, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulated+gene+expression+systems.">Regulated gene expression systems.</a> Gene Ther. 7 (2), 120-125 (2000).</li><li>Suzuki, Y., Suzuki, Y., Xu, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+regulatable+lentiviral+system.">Gene regulatable lentiviral system.</a> Viral Gene Therapy. , 285-309 (2011).</li><li>Gossen, M., Bujard, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tight+control+of+gene+expression+in+mammalian+cells+by+tetracycline-responsive+promoters.">Tight control of gene expression in mammalian cells by tetracycline-responsive promoters.</a> Proc. Natl. Acad. Sci. 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We have no conflicts of interest related to this report.

The main drawback of using a binary gene expression switch is the need to simultaneously deliver two separate plasmids (driver and effector) into the target cell. This can lead to an unequal distribution of plasmids and result in an inconsistent response of the switch to the inducers1,2,3. Another shortcoming of the two-vector system is that a minimum of two rounds of antibiotic selection are required to identify promising cell ...

Several different gene switches have been explored for their ability to precisely regulate transgene expression in cell culture and animal models, with varying degrees of success1,2,3. Potential gene switch systems should meet several stringent criteria, including: precise directional expression of the transgene, dosage- and time-dependent responsiveness to inducers, negligible leakiness of the promoter, reversibility of transgene activation through inducer removal, and inducer toxicity levels tolerable to cell lines and laboratory animals1,2,3. Several small molecule inducers have been exploited, including tetracycline4,5, rapamycin6,7,8, mifepristone9,10, and ecdysone11,12,13,14. In general, these systems require at least two plasmids containing two or three discrete expression units, one or two of which compose a regulatory element (inducer plasmid) that binds a small molecule inducer to gain transcriptional activity; and another plasmid (effector plasmid) containing the transgene under the control of a regulatory DNA region that allows the access of the inducer-bound regulatory element. The main drawback of the binary system is that it requires the concomitant introduction of two vectors (inducer and effector) into the target cell. In transient transgene expression experiments, the simultaneous transfection of two plasmids inevitably produces a population of cells that is singly transfected with either the inducer or the effector, or co-transfected unequally. In addition, the binary system requires at least two rounds of antibiotic selection to establish stable cell lines, which is time-consuming and laborious. Thus, combining all of the components required for transgene expression and regulation into a single vector would be ideal to guarantee the concomitant expression of all the required elements in a single cell and allow for the regulation of transgene expression through treatment with small molecule inducers.
To overcome the shortcomings of binary gene switches, we recently developed a singular gene switch, using a Drosophila melanogaster EcR-based gene inducible system15. Ecdysone mediates gene expression when it binds to the EcR/ultraspiracle (USP) heterodimer, which in turn induces binding of the EcR to DNA regulatory elements3,11. The vertebrate retinoid X receptor (RXR), an ortholog of insect USP, recruits EcR to form an active transcriptional activator16. Thus, for the targeted expression of a transgene in vertebrate cells or tissue, the EcR and RXR must be co-expressed simultaneously before being stimulated by ecdysone or its agonists. Since the heterodimeric feature of the EcR-based gene switch can be influenced by the endogenous RXR level, Padidam et al. replaced the EcR DNA-binding and activation domains with heterologous GAL4 DNA-binding, herpes simplex virus protein vmw65 (VP16) activation domains fused to the EcR ligand-binding domain, which then became unresponsive to endogenous RXR and formed a homodimer to gain transcriptional activity17. The EcR-based gene switch was further improved by constructing a chimeric protein comprised of minimal VP16 activation domain combined with GvEcR, which formed a homodimer and localized in the cytosol in the absence of the ecdysone agonist, Teb16,18. By binding to Teb, the GvEcR changed its subcellular localization from the cytosol to the nucleus to recognize a hybrid promoter comprised of zebrafish E1b minimal promoter combined with a ten tandem repeated upstream activation sequences (UASs) to initiate the transcription of the target gene16.
To simplify the previously reported EcR-based gene switches16,18, we combined the binary features of the system into a single vector equipped with all the required elements for stimulating transgene expression, and then designated the newly generated vector, pEUI(+) (GenBank accession number: KP123436, Figure 1A)15. The effector responding to the GvEcR driver (hereafter driver) consists of ten tandem UAS repeats next to an E1b minimal promoter followed by a multiple cloning site (MCS) with EcoRI, PmlI, NheI, BmtI, AfeI, and AflII recognition sequences (Figure 1B). Additionally, to facilitate the selection of transfected cells, an SV40 promoter-driven puromycin N-acetyl-transferase (PAC) gene was placed between the driver and effector regions to maintain stable cell lines (Figure 1).
We describe a detailed protocol for the transient and stable modulation of transgene expression using pEUI(+). In addition, we provide detailed instructions for the successful use of Teb as an ecdysone agonist.

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">pEUI(+)</td>
			<td style="width:71px;">TransLab</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">The patent license was transferred to TransLab Inc.&#160;</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Gene-Fect Transfection Reagent</td>
			<td style="width:71px;">TransLab</td>
			<td style="width:119px;">TLC-001</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HEK293</td>
			<td style="width:71px;">ATCC</td>
			<td style="width:119px;">CRL-1573</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tebufenozide</td>
			<td style="width:71px;">Fluka</td>
			<td style="width:119px;">31652</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cloning cylinder</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">CLS31668</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Puromycin</td>
			<td style="width:71px;">Corning</td>
			<td style="width:119px;">58-58-2</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Antibiotics</td>
			<td style="width:71px;">Gibco</td>
			<td style="width:119px;">15240-062</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Trypsin-EDTA</td>
			<td style="width:71px;">Welgene</td>
			<td style="width:119px;">LS015-01</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">DMEM</td>
			<td style="width:71px;">Welgene</td>
			<td style="width:119px;">LM001-05</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fetal Bovine Serum</td>
			<td style="width:71px;">Welgene</td>
			<td style="width:119px;">S001-01</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Cell culture dish</td>
			<td style="width:71px;">SPL life science</td>
			<td style="width:119px;">11090</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">mouse FLAG M2</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">F3165</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">anti-alpha tubulin antibody</td>
			<td style="width:71px;">Calbiochem</td>
			<td style="width:119px;">CP06</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Cloning cylinder</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">CLS31668</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">NucleoBond Xtra Midi</td>
			<td style="width:71px;">Macherey-Nagel</td>
			<td style="width:119px;">740410.1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">M-PER Mammalian Protein 
			Extraction Reagent</td>
			<td style="width:71px;">Thermo Fisher</td>
			<td style="width:119px;">78505</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">100X Protease inhibitor Cock. III</td>
			<td style="width:71px;">T&#38;I</td>
			<td style="width:119px;">BPI-9200</td>
			<td></td>
		</tr>
	</tbody>
</table>

an ecdysone receptor-based singular gene switch for deliberate expression of transgene with robustness, reversibility, and negligible leakiness

Precise control of transgene expression is desirable in biological and clinical studies. However, because the binary feature of currently employed gene switches requires the transfer of two therapeutic expression units concurrently into a single cell, the practical application of the system for gene therapy is limited. To simplify the transgene expression system, we generated a gene switch designated as pEUI(+) encompassing a complete set of transgene expression modules in a single vector. Comprising of the GAL4 DNA-binding domain and modified EcR (GvEcR), a minimal VP16 activation domain fused with a GAL4 DNA-binding domain, as well as a modified Drosophila ecdysone receptor (EcR), the newly developed singular gene switch is highly responsive to the administration of a chemical inducer in a time- and dosage-dependent manner. The pEUI(+) vector is a potentially powerful tool for improving the control of transgene expression in both biological research and pre-clinical studies. Here, we present a detailed protocol for modulation of a transient and stable transgene expression using pEUI(+) vector by the treatment of tebufenozide (Teb). Additionally, we share important guidelines for the use of Teb as a chemical inducer.

The GvEcR-based singular gene switch is depicted in Figure 1A. The pEUI(+) vector was optimized for regulated transgene expression by the treatment with Teb. The effector region of pEUI(+) comprises a 10xUAS and an E1b minimal promoter followed by an MCS containing EcoRI, PmlI, NheI, BmtI, AfeI, and AflII restriction enzyme recognition sites. An SV40 poly(A) signal was added behind the MCS (Figure 1B). A PAC gene was ins...

Watch this Scientific Journal Video about An Ecdysone Receptor-based Singular Gene Switch for Deliberate Expression of Transgene with Robustness, Reversibility, and Negligible Leakiness at JoVE.com

An Ecdysone Receptor-based Singular Gene Switch for Deliberate Expression of Transgene with Robustness, Reversibility, and Negligible Leakiness

Here, we present a protocol for the modulation of transgene expression using pEUI(+) singular gene switch by tebufenozide treatment.

Precise control of transgene expression is desirable in biological and clinical studies. However, because the binary feature of currently employed gene ...

The overall goal of this experiment is to modulate transgene expression by the administration of the chemical inducer tebufenozide. This method can help answer key questions in the cell and molecular biology field, such as when you need to stimulate the expression of a gene of interest at a desired time with a desired strength. The main advantage of this technique is that by combining all the required elements for transgene expression within a single vector, transgene expression can be stimulated by the administration of the chemical inducer tebufenozide.After subcloning the EGFP or ANKRD13A transgenes according to the text protocol, prepare four cell culture dishes containing freshly passaged HEK 293 cells in five milliliters of DMEM supplemented with five to 10%FBS and antibiotics, which will hereafter be referred to as culture medium. Maintain the cells at 37 degrees Celsius. When the cells reach 50 to 60%density, add three microliters of transfection reagent to 200 microliters of diluent containing the DNA.After incubating the reaction at room temperature for 30 minutes, add the mixture to the HEK 293 cells. Use two dishes for transfection, and leave the other two untreated as controls. Incubate the cells at 37 degrees Celsius for 12 to 24 hours.Following the incubation, add Teb to one of the transfected samples and to one of the non-transfected controls. Leave the other two samples untreated as experimental controls. Incubate the plates for 12 to 48 hours.If using the EGFP insert, analyze EGFP expression under a fluorescent microscope. Otherwise, to harvest the cells for immunoblotting, use ice-cold PBS to rinse the cells twice. Then, use a cell scraper to remove them from the plate, and transfer them into a 15-milliliter conical tube.Next, spin the tubes at 21, 000 times g and 18 to 25 degrees Celsius for two minutes. Then, after discarding the PBS, add 0.5 milliliters of ice-cold mammalian protein extraction reagent, or M-PER, and protease inhibitor to the pellet. Resuspend the cells with several rounds of pipetting.Then, incubate the cell suspension at 18 to 25 degrees Celsius and room temperature for 15 minutes. Spin the cell lysate at 21, 000 times g and four degrees Celsius for 10 minutes. Then, transfer the aqueous supernatant into a fresh 1.5-milliliter microcentrifuge tube, and analyze it by immunoblotting with the appropriate antibodies.To quench the Teb stimuli, remove the Teb containing culture medium from the cells, and use pre-warmed PBS to rinse the cells twice. Then, add one milliliter of 0.25%trypsin/EDTA, and incubate the cells at 37 degrees Celsius for one minute. Add 10 milliliters of pre-warmed, Teb-free culture medium to the cells, and use a cell scraper to harvest them.Transfer the cells to a 15-milliliter conical tube. Then, spin the cells at 21, 000 times g and 18 to 25 degrees Celsius for two minutes. Resuspend the cells in 50 milliliters of pre-warmed, Teb-free culture medium, and transfer five milliliters of the cells into three 60-millimeter fresh cell culture dishes.Incubate the cells at 37 degrees Celsius for 24, 48, and 72 hours, respectively. Finally, harvest the cells at different time points, and measure the expression levels of the transgene using immunoblotting. In this experiment that evaluated the activity and leakiness of pEUI-plus-EGFP, mock vector transfectants showed no fluorescent signal regardless of Teb treatment.However, pEUI-plus-EGFP transfectants became progressively sensitized to the increasing amount of Teb. More importantly, pEUI-plus-EGFP transfectants not treated with Teb did not elicit any detectable EGFP signals. FLAG-tagged ANKRD13A was used to further validate the responsiveness of pEUI-plus to Teb.As shown in this western blot using anti-FLAG antibodies, transfected HEK 293 cells exhibited strong ANKRD13A expression following a 24-hour treatment with Teb. In addition, depletion of Teb demonstrated the reversibility of the pEUI-plus gene switch, as ANKRD13A was no longer detectable in cells cultured without Teb. Once mastered, this technique can be done in one hour if it is performed properly.While attempting this procedure, it's important to remember to carry out almost all the experiment under germ-free conditions. Following this procedure, other methods, like the Tet-On or Tet-Off system can be applied to differentially express two distinct transgenes. After its development, this technique paved the way for researchers in the field of cell biology to explore molecular physiology at the cellular level.After watching this video, you should have a good understanding of how to use the pEUI-plus gene switch vector for the purpose of inducing transgene expression at a desired time with a desired strength. Don't forget that working with tebufenozide can be hazardous and precautions, such as wearing a lab coat, should always be taken while performing this procedure.

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6.4K vistas.  Chungnam National University. The overall goal of this experiment is to modulate transgene expression by the administration of the chemical inducer tebufenozide. This method can help answer key questions in the cell and molecular biology field, such as when you need to stimulate the expression of a gene of interest at a desired time with a desired strength. The main advantage of this technique is that by combining all the required elements for transgene expression within a single vector, transgene expression can be stimul...