Team:Slovenia/Modeling

From 2012.igem.org

(Difference between revisions)
 
(12 intermediate revisions not shown)
Line 2: Line 2:
<head>
<head>
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
 +
 +
<!-- back to top -->
 +
<div style="position:fixed; bottom:45px; right:30px; width:100px; height:66px; background-color:transparent;">
 +
<a href="#topofthepage">
 +
<table style="background-color:transparent;" onclick="window.location = '#topofthepage'" class="invisible" style="height:100%;">
 +
<tr class="invisible" style="background-color:transparent;">
 +
<td class="invisible" style="background-color:transparent;" valign="center">
 +
<img width="100px" src ="https://static.igem.org/mediawiki/2012/1/14/Svn12_hp_btt.png"></img>
 +
</td></tr></table>
 +
</a>
 +
</div>
<style type="text/css">
<style type="text/css">
Line 201: Line 212:
#cssmenu ul li > ul li{display:block; list-style:inside none; padding:0; margin:0; position:relative;}  
#cssmenu ul li > ul li{display:block; list-style:inside none; padding:0; margin:0; position:relative;}  
#cssmenu ul li > ul li a{ outline:none; display:block; position:relative; margin:0; padding:8px 20px; font:10pt Arial, Helvetica, sans-serif; color:#fff; text-decoration:none; text-shadow:1px 1px 0 rgba(0,0,0, 0.5); }  
#cssmenu ul li > ul li a{ outline:none; display:block; position:relative; margin:0; padding:8px 20px; font:10pt Arial, Helvetica, sans-serif; color:#fff; text-decoration:none; text-shadow:1px 1px 0 rgba(0,0,0, 0.5); }  
 +
#cssmenu ul li > ul li a table tr td span{ outline:none; display:block; position:relative; margin:0; padding:0px 0px; font:10pt Arial, Helvetica, sans-serif; color:#fff; text-decoration:none; text-shadow:1px 1px 0 rgba(0,0,0, 0.5); }
#cssmenu, #cssmenu > ul > li > ul > li a:hover
#cssmenu, #cssmenu > ul > li > ul > li a:hover
{ background:#043A6B;  
{ background:#043A6B;  
Line 216: Line 228:
#cssmenu > ul > li > a:hover{background:#0C5DA5;}  
#cssmenu > ul > li > a:hover{background:#0C5DA5;}  
/* end CSS navigation menu (blue) */
/* end CSS navigation menu (blue) */
 +
 +
/*new table start*/
 +
table.newtable {background-color:transparent;}
 +
td.newtable, th.newtable {background-color:transparent;}
 +
thead.newtable{ }
 +
tbody .newtable{}
 +
/*new table*/
Line 292: Line 311:
<body>
<body>
 +
 +
<a name="topofthepage" style="background-color:transparent;"></a>
 +
<div id="banner">
<div id="banner">
-
<a style="position:absolute; top:0px; left:490px;" href="https://2012.igem.org/Main_Page"><b>iGEM 2012</b></a>
 
</div>
</div>
Line 317: Line 338:
<li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchDesignedTALregulators'><span>Designed TAL regulators</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchDesignedTALregulators'><span>Designed TAL regulators</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchMutualRepressorSwitch'><span>Mutual repressor switch</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchMutualRepressorSwitch'><span>Mutual repressor switch</span></a></li>  
-
<li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchPositiveFeedbackLoopSwitch'><span>Positive feedback loop switch</span></a></li>  
+
<li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchPositiveFeedbackLoopSwitch'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/TheSwitchPositiveFeedbackLoopSwitch';" class="newtable"><tr class="newtable"><td class="newtable"><span>Positive feedback loop switch</span></td><td class="newtable"><img style="margin-right:-15px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>
 +
    <li><a href='https://2012.igem.org/Team:Slovenia/TheSwitchControls'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/TheSwitchControls';" class="newtable"><tr class="newtable"><td class="newtable"><span>Controls</span></td><td class="newtable"><img style="margin-right:-81px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>  
  </ul>
  </ul>
</li>
</li>
Line 325: Line 347:
<li><a href='https://2012.igem.org/Team:Slovenia/SafetyMechanismsEscapeTag'><span>Escape tag</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/SafetyMechanismsEscapeTag'><span>Escape tag</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/SafetyMechanismsTermination'><span>Termination</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/SafetyMechanismsTermination'><span>Termination</span></a></li>  
-
<li><a href='https://2012.igem.org/Team:Slovenia/SafetyMechanismsMicrocapsuleDegradation'><span>Microcapsule degradation</span></a></li>  
+
    <li><a href="https://2012.igem.org/Team:Slovenia/SafetyMechanismsMicrocapsuleDegradation"><table  onclick="window.location = 'https://2012.igem.org/Team:Slovenia/SafetyMechanismsMicrocapsuleDegradation';" class="newtable"><tr class="newtable"><td class="newtable"><span>Microcapsule degradation</span></td><td class="newtable"><img style="margin-right:-15px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>  
  </ul>
  </ul>
</li>
</li>
Line 333: Line 355:
<li><a href='https://2012.igem.org/Team:Slovenia/ImplementationHepatitisC'><span>Hepatitis C</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ImplementationHepatitisC'><span>Hepatitis C</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ImplementationIschaemicHeartDisease'><span>Ischaemic heart disease</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/ImplementationIschaemicHeartDisease'><span>Ischaemic heart disease</span></a></li>  
 +
    <li><a href='https://2012.igem.org/Team:Slovenia/ImplementationImpact'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/ImplementationImpact';" class="newtable"><tr class="newtable"><td class="newtable"><span>Impact</span></td><td class="newtable"><img style="margin-right:-86px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>
 
 
  </ul>
  </ul>
Line 340: Line 363:
  <ul>
  <ul>
<li><a href='https://2012.igem.org/Team:Slovenia/Modeling'><span>Overview</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/Modeling'><span>Overview</span></a></li>
-
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingPK'><span>Pharmacokinetics</span></a></li>
+
    <li><a href='https://2012.igem.org/Team:Slovenia/ModelingPK'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/ModelingPK';" class="newtable"><tr class="newtable"><td class="newtable"><span>Pharmacokinetics</span></td><td class="newtable"><img style="margin-right:-15px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingMethods'><span>Modeling methods</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingMethods'><span>Modeling methods</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingMutualRepressorSwitch'><span>Mutual repressor switch</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingMutualRepressorSwitch'><span>Mutual repressor switch</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingPositiveFeedbackLoopSwitch'><span>Positive feedback loop switch</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingPositiveFeedbackLoopSwitch'><span>Positive feedback loop switch</span></a></li>
-
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingQuantitativeModel'><span>Quantitative and stability model</span></a></li>  
+
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingQuantitativeModel'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/ModelingQuantitativeModel';" class="newtable"><tr class="newtable"><td class="newtable"><span>Experimental model</span></td><td class="newtable"><img style="margin-right:-15px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>  
-
<li><a href='https://2012.igem.org/Team:Slovenia/ModelingInteractiveSimulations'><span>Interactive simulations</span></a></li>
+
    <li><a href='https://2012.igem.org/Team:Slovenia/ModelingInteractiveSimulations'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/ModelingInteractiveSimulations';" class="newtable"><tr class="newtable"><td class="newtable"><span>Interactive simulations</span></td><td class="newtable"><img style="margin-right:-15px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>
  </ul>
  </ul>
</li>
</li>
Line 356: Line 379:
  <ul>
  <ul>
<li><a href='https://2012.igem.org/Team:Slovenia/Notebook'><span>Experimental methods</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/Notebook'><span>Experimental methods</span></a></li>
-
<li><a href='https://2012.igem.org/Team:Slovenia/NotebookLablog'><span>Lablog</span></a></li>
+
    <li><a href='https://2012.igem.org/Team:Slovenia/NotebookLablog'><table onclick="window.location = 'https://2012.igem.org/Team:Slovenia/NotebookLablog';" class="newtable"><tr class="newtable"><td class="newtable"><span>Lablog</span></td><td class="newtable"><img style="margin-right:-90px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/NotebookLabSafety'><span>Lab safety</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/NotebookLabSafety'><span>Lab safety</span></a></li>  
  </ul>
  </ul>
Line 379: Line 402:
<li><a href='https://2012.igem.org/Team:Slovenia/Team'><span>Team members</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/Team'><span>Team members</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/TeamAttributions'><span>Attributions</span></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/TeamAttributions'><span>Attributions</span></a></li>
 +
<li><a href='https://2012.igem.org/Team:Slovenia/TeamCollaborations'><table  onclick="window.location = 'https://2012.igem.org/Team:Slovenia/TeamCollaborations';" class="newtable"><tr class="newtable"><td class="newtable"><span>Collaborations</span></td><td class="newtable"><img style="margin-right:-20px;" width="25px" src="https://static.igem.org/mediawiki/2012/e/ee/Svn12_hp_new.png"></img></td></tr></table></a></li>
<li><a href='https://2012.igem.org/Team:Slovenia/TeamGallery'><span>Gallery</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/TeamGallery'><span>Gallery</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/TeamSponsors'><span>Sponsors</span></a></li>  
<li><a href='https://2012.igem.org/Team:Slovenia/TeamSponsors'><span>Sponsors</span></a></li>  
Line 386: Line 410:
</div>
</div>
<!-- end main menu -->
<!-- end main menu -->
 +
 +
 +
 +
</div> <!-- end menu -->
</div> <!-- end menu -->
 +
 +
<div id="main">
<div id="main">
<br/>
<br/>
<h1>Modeling overview</h1>
<h1>Modeling overview</h1>
 +
 +
<!-- dummy link na bannerju -->
 +
<a href="https://2012.igem.org/Main_Page">
 +
<div id="dummy" style="background-color:transparent; position:absolute; left:870px; top:25px; width:115px; height:80px; z-index:100; opacity:0.0;">
 +
</div>
 +
</a>
<!-- summary table -->
<!-- summary table -->
Line 398: Line 434:
<tr class="summary">
<tr class="summary">
<td class="summary" style="font-size:110%;">
<td class="summary" style="font-size:110%;">
-
<p>Distribution of drugs throughout tissues is very important for the effective therapy. We built pharmacokinetic models to simulate distribution of biological drugs produced by the engineered microencapsulated cells for implantation into the liver to treat hepatitis C and into the muscle tissue for the therapy of myocardial ischemia in comparison to the standard therapy.</p>
 
<p>
<p>
-
Pharmacokinetic models suggest that the proposed type of delivery should decrease the systemic side effects and the required dose of biological drugs.
+
<b style="font-size:120%;">Pharmacokinetic modeling</b>
 +
<p>
 +
Distribution of drugs throughout tissues is very important for the effective therapy. We built <b>pharmacokinetic models</b> to simulate distribution of biological drugs produced by the engineered microencapsulated cells which would be implanted into the liver to treat hepatitis C and into the heart for the therapy of myocardial ischaemia, in comparison to the standard therapy.</p>
 +
<p>
 +
Pharmacokinetic models suggest that <b>the proposed type of delivery should decrease the systemic side effects and the required dose of biological drugs.</b>
</p>
</p>
-
+
</p>
 +
 
 +
 
 +
<br/><br/>
 +
<p>
 +
<b style="font-size:120%;">Modeling of epigenetic switches</b>
<p>
<p>
-
Mathematical modeling was used to simulate different types of epigenetic switches (mutual repressor switch, based on the classical toggle switch and its extended version with introduction of additional positive feedback loops), where experimental parameters were incorporated into the model. Our models led to some non-intuitive results concerning the introduction of non-linearity into the system, which was verified by experimental results.
+
Mathematical modeling was used to simulate different types of epigenetic switches (mutual repressor switch, based on the classic toggle switch and its extended version with introduction of additional positive feedback loops), where experimental parameters were incorporated into the model. Our models led to some non-intuitive results concerning the introduction of non-linearity into the system, which was verified by experimental results.
</p>
</p>
<p>
<p>
-
We constructed deterministic and stochastic models to analyze both of our switches and developed two additional modeling approaches:
+
We constructed <b>deterministic and stochastic models</b> to analyze both of our switches and developed <b>two new modeling approaches</b>:
<ul style="margin-left:30px;">
<ul style="margin-left:30px;">
-
     <li>a quantitative model based on the available experimental data;</li>
+
     <li><b><a href="https://2012.igem.org/Team:Slovenia/ModelingQuantitativeModel">an experimental model</a></b> based on the available experimental data;</li>
-
     <li>a new modeling algorithm, called C#Sim, based on object-oriented programming approach.</li>
+
     <li><b><a href="https://2012.igem.org/Team:Slovenia/ModelingMethods#csim">a new modeling algorithm</a></b>, called C#Sim, based on object-oriented programming approach.</li>
</ul>
</ul>
 +
</p>
</p>
</p>
 +
<br/><br/>
 +
<p>
 +
<b style="font-size:120%;">What did the dry-lab analysis of epigenetic switches show?</b>
<p>
<p>
All models consistently demonstrate that:
All models consistently demonstrate that:
Line 422: Line 470:
</ul>
</ul>
</p>
</p>
 +
</p>
 +
 +
<p>
 +
Therefore we predicted that the mutual repressor switch would not exhibit bistable behavior, while the positive feedback loop switch should be stable. These assessments were confirmed by experimental results, with the positive feedback loop switch clearly exhibiting bistability.
 +
</p>
 +
 +
<br/><br/>
<p>
<p>
-
Therefore, we predicted that the mutual repressor switch would not exhibit bistable behavior, while the positive feedback loop switch should be stable. These assessments were confirmed by experimental results, with the positive feedback loop switch clearly exhibiting bistability.  
+
<b style="font-size:120%;">How did modeling help our project?</b>
 +
<p>Pharmacokinetic model made it possible to compare conventional and our therapy and to calculate required drug production in microencapsulated cells.</p>
 +
<p>Modeling of epigenetic switches and thorough parameter space analysis made it possible to provide our wet-lab with answers to questions regarding how our switches may behave in different scenarios - e.g., how different amounts of constructs defining the positive feedback loop switch may affect bistability, what is the effect of leaky transcription, can the positive feedback loops replace the need for transcription factor cooperativity to obtain bistability, why the mutual repressor switch may not work, etc. This way, our experimental work was interwoven with dry-lab modeling.</p>
</p>
</p>
Line 436: Line 493:
<p>
<p>
A pharmacokinetic model was built to simulate drug distribution troughout body tissues. We used physiologically based design to construct a mathematical model and predict drug kinetics. Several models were built to compare standard therapies with localized therapeutical cells.</p><p>
A pharmacokinetic model was built to simulate drug distribution troughout body tissues. We used physiologically based design to construct a mathematical model and predict drug kinetics. Several models were built to compare standard therapies with localized therapeutical cells.</p><p>
-
Calculations show that localized drug production accounts for better concentration ratios between target and non-target tissues and also maintains steady concentration levels through time. This has a potential to avoid many of the side effects with common therapies. In addition, with this therapy, drug concentration does not fluctuate as in standard therapy. Peaks in concentration contribute to side-effects, while decreases in concentrations cause lower therapeutical effectiveness. Results suggest this prospective treatment provides a more efficient and safe alternative.
+
Calculations show that localized drug production accounts for better concentration ratios between target and non-target tissues and also maintains steady concentration levels through time. This has a potential to avoid many of the side effects with common therapies. In addition, with this therapy, drug concentration does not fluctuate as in standard therapy. Peaks in concentration contribute to side-effects while decreases in concentrations cause lower therapeutical effectiveness. Results suggest this prospective treatment provides a more efficient and safe alternative.
Line 461: Line 518:
<h2>Deterministic and stochastic modeling</h2>
<h2>Deterministic and stochastic modeling</h2>
-
<p>We modeled the mutual repressor switch and the positive feedback loop switch using deterministic and stochastic modeling approach. The deterministic model was based on the probabilistic interpretation of gene regulation and formalized as a set of ordinary differential equations. For each promoter, the probability of it being in an active state (i.e. a state lading to gene expression) was formulated mathematically, considering transcription factors bound to the corresponding binding sites. In this way, binding of an activator would result in activation of transcription from the minimal promoter, while binding of a repressor would result in an inactive promoter. Stochastic models were formulated as a set of reactions describing the dynamics of a switch and simulated using stochastic simulation algorithm.
+
<p>We modeled the mutual repressor switch and the positive feedback loop switch using deterministic and stochastic modeling approach. The deterministic model was based on the probabilistic interpretation of gene regulation and formalized as a set of ordinary differential equations. For each promoter, the probability of it being in an active state (i.e. a state leading to gene expression) was formulated mathematically, considering transcription factors bound to the corresponding binding sites. In this way, binding of an activator would result in activation of transcription from the minimal promoter, while binding of a repressor would result in an inactive promoter. Stochastic models were formulated as a set of reactions describing the dynamics of a switch and simulated using stochastic simulation algorithm.
Line 477: Line 534:
<tbody  class="invisible">
<tbody  class="invisible">
<tr class="normal"><td class="invisible">
<tr class="normal"><td class="invisible">
-
<b>Figure 2.</b> The positive feedback loop switch exhibiting bistability in a stochastic simulation, even in the presence of leaky transcription of designed TAL repressors and no cooperativity.  The mutual repressor switch did not exhibit bistability in such conditions. Reporter concentrations are depicted as a function of time.
+
<b>Figure 2.</b> The positive feedback loop switch exhibiting bistability in a stochastic simulation even in the presence of leaky transcription of designed TAL repressors and no cooperativity.  The mutual repressor switch did not exhibit bistability in such conditions. Reporter concentrations are depicted as a function of time.
</td></tr>
</td></tr>
</tbody>
</tbody>
Line 486: Line 543:
-
<h2>Quantitative modeling</h2>
+
<h2>Experimental modeling</h2>
<p>
<p>
-
A quantitative model of switch dynamics extracted simulation parameters from the available experimental data of gene regulation and results obtained from our experiments using TAL regulators. This model also predicted that the positive feedback loop switch exhibits bistability without cooperative DNA binding.
+
An experimental model of switch dynamics extracted simulation parameters from the available experimental data of gene regulation and results obtained from our experiments using TAL regulators. This model also predicted that the positive feedback loop switch exhibits bistability without cooperative DNA binding.
</p>
</p>
Line 530: Line 587:
<!-- end table-->
<!-- end table-->
-
 
-
<h2>Source code</h2>
 
-
<p>
 
-
Our modeling-related source code can be found <a href="https://2012.igem.org/Team:Slovenia/SourceCode">here</a>.
 
-
</p>
 

Latest revision as of 20:56, 26 October 2012


Modeling overview

Pharmacokinetic modeling

Distribution of drugs throughout tissues is very important for the effective therapy. We built pharmacokinetic models to simulate distribution of biological drugs produced by the engineered microencapsulated cells which would be implanted into the liver to treat hepatitis C and into the heart for the therapy of myocardial ischaemia, in comparison to the standard therapy.

Pharmacokinetic models suggest that the proposed type of delivery should decrease the systemic side effects and the required dose of biological drugs.



Modeling of epigenetic switches

Mathematical modeling was used to simulate different types of epigenetic switches (mutual repressor switch, based on the classic toggle switch and its extended version with introduction of additional positive feedback loops), where experimental parameters were incorporated into the model. Our models led to some non-intuitive results concerning the introduction of non-linearity into the system, which was verified by experimental results.

We constructed deterministic and stochastic models to analyze both of our switches and developed two new modeling approaches:



What did the dry-lab analysis of epigenetic switches show?

All models consistently demonstrate that:

  • the mutual repressor switch is unlikely to exhibit bistability in a realistic experimental setting using monomeric transcription factors;
  • the positive feedback loop switch is, in terms of robustness, far superior to the mutual repressor switch based on non-cooperative orthogonal DNA-binding domains of transcription factors, exhibiting bistability in more demanding (non-ideal) conditions.

Therefore we predicted that the mutual repressor switch would not exhibit bistable behavior, while the positive feedback loop switch should be stable. These assessments were confirmed by experimental results, with the positive feedback loop switch clearly exhibiting bistability.



How did modeling help our project?

Pharmacokinetic model made it possible to compare conventional and our therapy and to calculate required drug production in microencapsulated cells.

Modeling of epigenetic switches and thorough parameter space analysis made it possible to provide our wet-lab with answers to questions regarding how our switches may behave in different scenarios - e.g., how different amounts of constructs defining the positive feedback loop switch may affect bistability, what is the effect of leaky transcription, can the positive feedback loops replace the need for transcription factor cooperativity to obtain bistability, why the mutual repressor switch may not work, etc. This way, our experimental work was interwoven with dry-lab modeling.

Pharmacokinetic modeling

A pharmacokinetic model was built to simulate drug distribution troughout body tissues. We used physiologically based design to construct a mathematical model and predict drug kinetics. Several models were built to compare standard therapies with localized therapeutical cells.

Calculations show that localized drug production accounts for better concentration ratios between target and non-target tissues and also maintains steady concentration levels through time. This has a potential to avoid many of the side effects with common therapies. In addition, with this therapy, drug concentration does not fluctuate as in standard therapy. Peaks in concentration contribute to side-effects while decreases in concentrations cause lower therapeutical effectiveness. Results suggest this prospective treatment provides a more efficient and safe alternative.

Deterministic and stochastic modeling

We modeled the mutual repressor switch and the positive feedback loop switch using deterministic and stochastic modeling approach. The deterministic model was based on the probabilistic interpretation of gene regulation and formalized as a set of ordinary differential equations. For each promoter, the probability of it being in an active state (i.e. a state leading to gene expression) was formulated mathematically, considering transcription factors bound to the corresponding binding sites. In this way, binding of an activator would result in activation of transcription from the minimal promoter, while binding of a repressor would result in an inactive promoter. Stochastic models were formulated as a set of reactions describing the dynamics of a switch and simulated using stochastic simulation algorithm.

Experimental modeling

An experimental model of switch dynamics extracted simulation parameters from the available experimental data of gene regulation and results obtained from our experiments using TAL regulators. This model also predicted that the positive feedback loop switch exhibits bistability without cooperative DNA binding.

C#Sim - a new object oriented hybrid modeling algorithm

We developed a new modeling algorithm, called C#Sim. This algorithm enabled us:

  • to explicitly model transcription factor binding, especially competitive binding of TAL activators and repressors to the same binding site, characteristic of our positive feedback loop switch;
  • to explicitly model a limited number of binding site repeats;
  • to incorporate the stochasticity of gene expression into an otherwise deterministic approach.

The algorithm was designed in a modular, object-oriented way, allowing us to represent each mRNA and protein molecule as a separate entity with its own set of parameters. With C#Sim, gene regulatory networks can easily be constructed using a programming language and simulated as a series of related entities (i.e. objects) such as promoters, binding sites and genes. The algorithm was implemented in C# programming language (Figure 3).

We modeled both the mutual repressor switch and the positive feedback loop switch using C#Sim. The results obtained led to the same conclusions as other modeling methods.


Next: Pharmacokinetic model >>