Team:Grenoble/Projet/Design/toggle

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<h2 id="toggle">Toggle switch explanation</h2>
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<h3>In a few words</h3>
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<h1>The Toggle Switch</h1>
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<a href="http://2011..org/wiki/images/a/a3/Toggle_Switch.png"><img src="https://static.igem.org/mediawiki/2011/a/a3/Toggle_Switch.png"  width="300px"></a>
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The Toggle Switch allows our bacterial strain to switch between one of the two different behaviors (Receiver or Sender) depending on the predominant concentration in the external medium: IPTG or Hg.
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We take into account two proteins repressing (LacI/MerR) each other's expression (pLac/pMerT). We create the fundaments of a toggle system that can switch when using two inducers in the medium: IPTG and Hg.
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Our project is based on a toggle switch system. So we have to explain how it works. Basically <u><b>it corresponds to an irreversible choice between two pathways depending on the environment.</b></u> In reality, the reversibility is possible but very difficult to obtain because of the strength of the interactions and the stability of the system (defined by hysteresis * insérer un lien ici*).
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Initially, both genes, MerR and LacI, are expressed repressing each other promoters: pLac and pMerT.
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<a href="https://static.igem.org/mediawiki/2011/2/2b/Toggle_car.png"><img height=350px width=550px src="https://static.igem.org/mediawiki/2011/2/2b/Toggle_car.png" alt="2 pathways toggle switch" title="Choose one way, no turning back !"></a>
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<h3 id="genet">Genetically, what is happening ?</h3>
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Contrary to us, bacteria can’t think or make voluntary choices. So how can they choose a pathway? Through our project, we are creating a genetic system which helps bacteria to take such a decision. For that, we exploit chemical components of the environment which influence the bacterial behaviour. By taking into account two proteins repressing each other’s expression (LacI and XR), we create the fundaments of a toggle system that can switch when using two inducers (IPTG and X) in the medium. </p>
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<p><a href="https://static.igem.org/mediawiki/2011/4/4a/Toggle.png"><img height=200px width=450px src="https://static.igem.org/mediawiki/2011/4/4a/Toggle.png" alt="toggle switch schema" title=""></a>
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  <td><a href="https://static.igem.org/mediawiki/2011/8/8d/Toggle3.png"><img src="https://static.igem.org/mediawiki/2011/5/5f/Toggle_Switch_Tet.png" alt="" title="" height=275px width=400px></a></td>
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  <td><p>Suppose that initially the genes in the Toggle Switch are both expressed.</p></td>
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On the plate where Hg concentration is the uppermost, this inducer will remove the repression exerted on pMerT promoter. So, the LacI proteins will be expressed and by repressing the promoter pLac, LacI proteins are shutting down the other pathway of the toggle.
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<a href="https://static.igem.org/mediawiki/2011/4/43/Toggle_Switch_predominance1.png"><img src="https://static.igem.org/mediawiki/2011/4/43/Toggle_Switch_predominance1.png" width="350px"></a>
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  <td><a href="https://static.igem.org/mediawiki/2011/0/0a/Toggle4.png"><img src="https://static.igem.org/mediawiki/2011/0/0a/Toggle4.png" alt="" title="" width="400"></a></td>
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<a href="https://static.igem.org/mediawiki/2011/d/d9/Toggle_Switch_predominance2_bis.png"><img src="https://static.igem.org/mediawiki/2011/d/d9/Toggle_Switch_predominance2_bis.png" width="350px"></a>
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If the effect of LacI is dominant through the presence of a high level of IPTG, the bacteria will synthesise more XR and switch off the expression of lacI
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Inversely, where IPTG concentration is the uppermost, the other pathway will be activated.
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  <td><a href="https://static.igem.org/mediawiki/2011/d/d5/Toggle5.png.png"><img src="https://static.igem.org/mediawiki/2011/d/d5/Toggle5.png" alt="" title="" width="400"></a></td>
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  <td><p>The bacteria toggle to one side and totally block the expression of lacI.</p></td>
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  <td><a href="https://static.igem.org/mediawiki/2011/1/15/Toggle6.png"><img src="https://static.igem.org/mediawiki/2011/1/15/Toggle6.png" alt="" title="" width="400"></a></td>
 
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  <td><p>We need to use very high level of the second inducer X to try to switch the toggle back because the active pathway creates an excess of XR, inhibiting lacI expression.</p></td>
 
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  <td><a href="https://static.igem.org/mediawiki/2011/9/97/Toggle7.png"><img src="https://static.igem.org/mediawiki/2011/9/97/Toggle7.png" alt="" title="" width="400"></a></td>
 
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  <td><p>The amount of X would have to be so high as to relieve the inhibition of lacI expression and consequently turn off the other pathway.</p></td>
 
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This toggle switch is one of <a href="https://2011.igem.org/Team:Grenoble/Projet/Modelling/Deterministic#Our_EquationsTS">our module of modelling</a>. The simulation obtained with this model are compared to the
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experiment <a href="https://2011.igem.org/Team:Grenoble/Projet/Results/Toggle">here</a>.
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<h3 id="proj">Importance of Toggle Switch for 'Le Projet'  ? </h3>
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Importance of Toggle Switch for Le Projet  ?
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Our Toggle switch is composed by the two repressors (LacI and TetR), also the ways express ether a Quorum Sensing receptor (CinR) or the Quorum Sensing synthesise enzyme (CinI). By this ways the bacterium will engage itself in secretion path or receptor path.
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That’s why we use Toggle Switch to have two different behaviours in one cell type, and simplify the immobilisation on plate. We use cell’s communication to finalise our biosensor so we need a homogeneous repartition of ‘sender cell’ and ‘receptor cell’ to have a good communication and response. So locate specifically (homogeneously) two type of cell, will be very hard work contrary to one ‘differentiable type cell’ that we can locate uniformly on the plate.
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    <option value="/regulation#rpos">The rpoS regulation system</option>
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Latest revision as of 00:37, 29 October 2011

Grenoble 2011, Mercuro-Coli iGEM


The Toggle Switch

The Toggle Switch allows our bacterial strain to switch between one of the two different behaviors (Receiver or Sender) depending on the predominant concentration in the external medium: IPTG or Hg.

We take into account two proteins repressing (LacI/MerR) each other's expression (pLac/pMerT). We create the fundaments of a toggle system that can switch when using two inducers in the medium: IPTG and Hg.

Initially, both genes, MerR and LacI, are expressed repressing each other promoters: pLac and pMerT.

On the plate where Hg concentration is the uppermost, this inducer will remove the repression exerted on pMerT promoter. So, the LacI proteins will be expressed and by repressing the promoter pLac, LacI proteins are shutting down the other pathway of the toggle.

Inversely, where IPTG concentration is the uppermost, the other pathway will be activated.

This toggle switch is one of our module of modelling. The simulation obtained with this model are compared to the experiment here.

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