The authors thank Christa Haase, Doris Weber and Brigitte Korte for technical assistance. Work in the Weidinger lab is supported by grants of the Deutsche Forschungsgemeinschaft WE 4223/3-1, WE 4223/4-1 and by the Deutsche Gesellschaft f&#252;r Kardiologie via an Oskar-Lapp-Stipendium and a Klaus-Georg-und-Sigrid-Hengstberger-Forschungsstipendium.

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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viral+2A+peptides+allow+expression+of+multiple+proteins+from+a+single+ORF+in+transgenic+zebrafish+embryos.">Viral 2A peptides allow expression of multiple proteins from a single ORF in transgenic zebrafish embryos.</a> Genesis. 45 (10), 625-629 (2007).</li><li>Suster, M. L., Abe, G., Schouw, A., Kawakami, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transposon-mediated+BAC+transgenesis+in+zebrafish.">Transposon-mediated BAC transgenesis in zebrafish.</a> Nat Protoc. 6 (12), 1998-2021 (2011).</li><li>Bussmann, J., Schulte-Merker, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+BAC+selection+for+tol2-mediated+transgenesis+in+zebrafish.">Rapid BAC selection for tol2-mediated transgenesis in zebrafish.</a> Development. 138 (19), 4327-4332 (2011).</li><li>Yuan, S., Sun, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microinjection+of+mRNA+and+morpholino+antisense+oligonucleotides+in+zebrafish+embryos.">Microinjection of mRNA and morpholino antisense oligonucleotides in zebrafish embryos.</a> J Vis Exp. 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R., Thummel, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+electroporation+of+morpholinos+into+the+regenerating+adult+zebrafish+tail+fin.">In vivo electroporation of morpholinos into the regenerating adult zebrafish tail fin.</a> J Vis Exp. (61), (2012).</li><li>Meeker, N. D., Hutchinson, S. A., Ho, L., Trede, N. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+for+isolation+of+PCR-ready+genomic+DNA+from+zebrafish+tissues.">Method for isolation of PCR-ready genomic DNA from zebrafish tissues.</a> Biotechniques. 43 (5), 610 (2007).</li><li>Thermes, V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=I-SceI+meganuclease+mediates+highly+efficient+transgenesis+in+fish.">I-SceI meganuclease mediates highly efficient transgenesis in fish.</a> Mech Dev. 118 (1-2), 91-98 (2002).</li><li>Suster, M. 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The authors have nothing to disclose.

The adult zebrafish has an amazing capacity to successfully regenerate many internal organs and appendages. A thorough understanding of the molecular and cellular mechanisms involved requires tissue-specific analysis of gene functions and signaling pathways. Towards this, the TetON system provides an efficient tool for spatiotemporally controlled gene expression in embryonic and adult zebrafish. The TetON system constructs and methodology described in this manuscript have been successfully used in a recent study of our l...

The zebrafish is a well-established vertebrate model organism to study many aspects of development, physiology, disease, and regeneration. With the growing adoption of zebrafish as a model for post-embryonic biological processes, experimental tools for inducible, tissue-specific manipulation of gene expression or signaling pathways have become increasingly important. Particularly, studies into organ and appendage regeneration in adult zebrafish have suffered from a lack of tools for dissection of the spatio-temporal requirements of signaling pathways during these regenerative processes.
Currently, three different systems have been used to achieve conditional, tissue-specific gene expression in regenerating organs of adult zebrafish: the Cre-lox system, mosaic expression of heat-shock inducible transgenes using transposon-mediated somatic transgenesis, and the TetON system1-3. TetON refers to a variant of a tetracycline-controlled transcriptional activation system, where expression is activated in the presence of the antibiotic tetracycline or a derivative, e.g. doxycycline. The Cre-lox system, as it has so far been used in adult fish, relies on a Tamoxifen-controlled Cre recombinase (CreERT2), whose expression is spatially restricted by tissue-specific regulatory elements. Cre-driven removal of a STOP cassette facilitates expression of the gene of interest driven by a promoter that should be active in all cell types1. Transposon-mediated creation of mosaically expressed somatic transgenes provides a system for inducible transgene expression in individual cell lineages. Injection of zebrafish embryos with a Tol2 transposon carrying a gene of interest under transcriptional control of a heat shock promoter results in chimeric individuals typically carrying the transgene only in discrete cell lineages of a regenerating organ2. While both systems allow for conditional tissue-specific gene expression, the Cre-lox system is not reversible, and the strategy using transposon-based clonal labeling suffers from its stochastic nature. Thus, we and others have recently adapted transgenic TetON systems for use in zebrafish, which facilitate temporally and spatially-controlled gene expression that is in addition tunable and reversible3-5.
The TetON system used here comprises a transgenic driver line (TetActivator) in which a Doxycycline (DOX)-inducible transcriptional activator (improved reverse tetracycline transactivator, irtTA, short TetA) is under control of tissue-specific genomic regulatory sequences. Secondly, it requires a transgenic responder line (TetResponder) that harbors a gene of interest under transcriptional control of the Tetracycline operator (Tet response element; TetRE) (Figure 1A). Thus, the use of specific combinations of TetActivator and TetResponder lines allows for conditional tissue-specific manipulation of gene expression.
We have recently utilized the TetON system to probe for tissue-specific functions of Wnt/beta&#8211;catenin signaling in the adult regenerating zebrafish tail fin3. In the protocol outlined here we describe a work flow for set-up and use of the TetON system in zebrafish, in particular for studies of fin regeneration. This includes detailed instructions on how to generate stable transgenic TetActivator and TetResponder lines and a protocol for transgene induction in embryos and adult zebrafish. Furthermore, we describe techniques for verification of tissue-specific gene expression in the fin regenerate, including a protocol for the preparation of cryosections of adult zebrafish fins. Additionally, we discuss considerations for the design of the TetActivator transgene, the choice of a transgenesis method, and detection of TetResponder expression. Hence, the overall goal of this protocol is to serve as a blueprint for setting-up a functional TetON system in zebrafish to achieve conditional tissue-specific gene expression, which can be applied to any tissue of interest.
We have created a TetActivator vector allowing for I-SceI or Tol2-mediated generation of stable TetActivator lines using short genomic regulatory sequences (enhancer fragments; Weidinger lab plasmid database no. 1247; Figure 1B). This construct contains a TetActivator cassette consisting of the M2 mutant variant of the reverse Tet repressor domain fused with the Herpes simplex virus VP16 transactivation domain-derivative 3F [irtTAM2(3F)]. Expression of the TetActivator (TetA) can be easily monitored since it is co-expressed with the fluorophore AmCyan from the same open reading frame; a p2a peptide mediates ribosomal skipping, which should result in production of TetA and AmCyan as separate proteins at a 1:1 ratio5,6. The construct also contains a poylinker 5&#8217; of the TetActivator cassette to facilitate insertion of genomic regulatory sequences of interest using conventional cloning methods.
Additionally, we have created a construct consisting of the above described TetActivator cassette plus a Kanamycin selection cassette (Weidinger lab plasmid database no. 1180; Figure 1C), which can be recombined into a bacterial artificial chromosome (BAC) containing a large genomic region (usually into the start codon of a gene whose expression pattern is to be mimicked by the transgene). Both constructs are available from the Weidinger lab upon request.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Breeding boxes</td>
			<td>Aqua Schwarz</td>
			<td>AquaBox 1</td>
			<td></td>
		</tr>
		<tr>
			<td>Compound fluorescent microscope</td>
			<td>e.g. Leica, Zeiss</td>
			<td>varies with the manufacturer</td>
			<td>to image fluorescent tissue sections</td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td>e.g. Leica, Zeiss</td>
			<td>varies with the manufacturer</td>
			<td>to image fluorescent tissue sections</td>
		</tr>
		<tr>
			<td>Cryostat</td>
			<td>e.g. Leica, Thermo-Scientific</td>
			<td>varies with the manufacturer</td>
			<td>for cryosectioning</td>
		</tr>
		<tr>
			<td>4&#8217;, 6- diamidino-2-phenylinodole (Dapi)</td>
			<td>Sigma-Aldrich</td>
			<td>D9542</td>
			<td>use 1/5000 in PBS 
			for visualization of nuclei</td>
		</tr>
		<tr>
			<td>Doxycycline</td>
			<td>Sigma-Aldrich</td>
			<td>D9891</td>
			<td>prepare stocks in 50% EtOH at 50 mg/ml (97 mM) 
			for TetResponder induction</td>
		</tr>
		<tr>
			<td>E3 embryo medium&#160;</td>
			<td></td>
			<td></td>
			<td>5 mM NaCl, 0.17 mM KCl, 0.33 mM CaCl2&#903; 2 H2O, 0.33 mM MgSO4&#903;7 H2O, 0.2 &#8240; (w/v) methylene blue, pH 6.5 
			for embryo/larvae husbandry</td>
		</tr>
		<tr>
			<td>Paraformaldehyde (PFA)</td>
			<td>Sigma-Aldrich</td>
			<td>P6148</td>
			<td>4 % (w/v) paraformaldehyde in PBS, pH 7.5 
			for fixation</td>
		</tr>
		<tr>
			<td>1x Phosphat-buffer saline (PBS)</td>
			<td></td>
			<td></td>
			<td>1.7 mM KH2PO4, 5.2 mM Na2HPO4, 150 mM NaCl, pH 7.5</td>
		</tr>
		<tr>
			<td>1x Phosphat-buffer saline + Tween 20 (PBT)</td>
			<td></td>
			<td></td>
			<td>1x PBS with 0.1 % Tween 20</td>
		</tr>
		<tr>
			<td>Superfrost Ultra Plus adhesion microscope slides</td>
			<td>Thermo Scientific&#160;</td>
			<td>1014356190</td>
			<td>for collection of tissue sections</td>
		</tr>
		<tr>
			<td>Stereo fluorescent microscope</td>
			<td>e.g. Leica, Zeiss</td>
			<td>varies with the manufacturer</td>
			<td>for fluorescence-based genotyping</td>
		</tr>
		<tr>
			<td>Thermocycler</td>
			<td>e.g. Biorad, Applied Biosystems</td>
			<td>varies with the manufacturer</td>
			<td>for PCR-based genotyping</td>
		</tr>
		<tr>
			<td>Tissue freezing medium (TFM)</td>
			<td>Triangel Biomedical Sciences</td>
			<td>TFM-C</td>
			<td>for embedding of tissue samples</td>
		</tr>
		<tr>
			<td>Tricaine (L-Ethyl-m-amino-benzoate-methane sulfonate/MS-222)</td>
			<td>Sigma-Aldrich</td>
			<td>E10521</td>
			<td>for anesthesia 
			use at 1 mg/ml in E3 embryo medium</td>
		</tr>
	</tbody>
</table>

use of the teton system to study molecular mechanisms of zebrafish regeneration

The zebrafish has become a very important model organism for studying vertebrate development, physiology, disease, and tissue regeneration. A thorough understanding of the molecular and cellular mechanisms involved requires experimental tools that allow for inducible, tissue-specific manipulation of gene expression or signaling pathways. Therefore, we and others have recently adapted the TetON system for use in zebrafish. The TetON system facilitates temporally and spatially-controlled gene expression and we have recently used this tool to probe for tissue-specific functions of Wnt/beta&#8211;catenin signaling during zebrafish tail fin regeneration. Here we describe the workflow for using the TetON system to achieve inducible, tissue-specific gene expression in the adult regenerating zebrafish tail fin. This includes the generation of stable transgenic TetActivator and TetResponder lines, transgene induction and techniques for verification of tissue-specific gene expression in the fin regenerate. Thus, this protocol serves as blueprint for setting up a functional TetON system in zebrafish and its subsequent use, in particular for studying fin regeneration.

To establish a functional TetON system for tissue-specific inducible gene expression, transgenic TetActivator and TetResponder lines need to be generated (Figure 1A). This is accomplished by microinjecting TetActivator (Figure 1B-C) or TetResponder (Figure 1E) constructs into early zebrafish embryos and subsequent germ-line integration. Functional TetActivator constructs can either be generated by cloning of short regulatory sequences (enhancer elements)...

Watch this Scientific Journal Video about Use of the TetON System to Study Molecular Mechanisms of Zebrafish Regeneration at JoVE.com

Use of the TetON System to Study Molecular Mechanisms of Zebrafish Regeneration

Here we outline the workflow for using the TetON system to achieve tissue-specific gene expression in the adult regenerating zebrafish tail fin.

The zebrafish has become a very important model organism for studying vertebrate development, physiology, disease, and tissue regeneration. A thorough ...

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10.5K Views.  Ulm University. Here we outline the workflow for using the TetON system to achieve tissue-specific gene expression in the adult regenerating zebrafish tail fin.