Team:Tokyo Tech

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== <font size=5>'''1 Our project''' </font>==
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== <font size=5>'''1. Our project''' </font>==
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<p><div>What is "<i style='mso-bidi-font-style:normal'>Coli</i> touch"?</div></p>
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<p><div><b>What is "<i style='mso-bidi-font-style:normal'>Coli</i> touch"?</b></div></p>
<div>“<i style='mso-bidi-font-style:normal'>Coli</i> Touch” has a pressure sensitive display composed of an <i style='mso-bidi-font-style:normal'>E. coli</i> lawn. When you touch its display, touched section is colored.</div>
<div>“<i style='mso-bidi-font-style:normal'>Coli</i> Touch” has a pressure sensitive display composed of an <i style='mso-bidi-font-style:normal'>E. coli</i> lawn. When you touch its display, touched section is colored.</div>
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<div>Next I'll tell you about “<i style='mso-bidi-font-style:normal'>Coli</i> Touch” work system. Display of “<i style='mso-bidi-font-style:normal'>Coli</i> Touch” has many <i style='mso-bidi-font-style:normal'>E. coli</i>. When you touch this display, pressure-input travels to <i style='mso-bidi-font-style:normal'>E. coli</i> in this display. And pressure applied <i style='mso-bidi-font-style:normal'>E. coli</i> expresses GFP.
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<div>Next I'll tell you about “<i style='mso-bidi-font-style:normal'>Coli</i> Touch” work system. Display of “<i style='mso-bidi-font-style:normal'>Coli</i> Touch” contains many <i style='mso-bidi-font-style:normal'>E. coli</i>. When you touch this display, pressure applies to <i style='mso-bidi-font-style:normal'>E. coli</i> in this display. Pressure applied <i style='mso-bidi-font-style:normal'>E. coli</i> expresses GFP.
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</div><p><div>Why pressure?</div></p>
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</div><p><div><b>Why pressure?</b></div></p>
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<p><div>“<i style='mso-bidi-font-style:normal'>Coli</i> Touch” uses pressure as input. Why we use pressure input? Past input ways (small molecule, heat and light) are difficult to induce uniformly.
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<p><div>“<i style='mso-bidi-font-style:normal'>Coli</i> Touch” uses pressure as input. Why do we use pressure? Past input methods (small molecules, heat and light) are difficult to induce uniformly.
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Pressure-input can induce uniformly.
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Pressure can induce uniformly.
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== <font size=5>'''2 Pressure induction'''</font> ==
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== <font size=5>'''2. Pressure induction'''</font> ==
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===<font size=3>'''Introduction'''</font>===
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<font size=3>'''Introduction'''</font>
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<div>It is known tet promoter sensitive to pressure. (T. Sato et al., 1995)</div><td>
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<div>Tet promoters is known as a sensitive ones to pressure. (T. Sato et al., 1995)</div><td>
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===<font size=3>'''Construction'''</font>===
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<font size=3>'''Construction'''</font>
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[[Image:Tech_Tet_figure1.jpg|400px|thumb|right|figure2-1. We constructed Ptet-GFP and promoter less-GFP for confirmatory experiment]]
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[[Image:Tech_Tet_figure1.jpg|400px|thumb|right|figure2-1. We constructed Ptet-GFP and promoter less-GFP.]]
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<div> We chose Tet promoter(Ptet) as pressure-inducible promoter.We constructed two plasmids - one is Ptet-GFP on <a href="http://partsregistry.org/Part:BBa_I739201">pSB6</a>. The other is promoter less-GFP on <a href="http://partsregistry.org/Part:BBa_I739201">pSB6</a> as a negative control.We experimented under 0.1 MPa and 30 MPa pressure.</div></td>
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<div> We chose the tet promoter (Ptet) as a pressure-inducible promoter. We constructed two plasmids - one is Ptet-GFP on <a href="http://partsregistry.org/Part:BBa_I739201">pSB6</a>. The other is promoter less-GFP on <a href="http://partsregistry.org/Part:BBa_I739201">pSB6</a> as a negative control. We measured activity of tet promoters under 0.1 MPa and 30 MPa without repressor protein.</div></td>
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===<font size=3>'''Result ~ activity of Ptet ~ '''</font>===
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<font size=3>'''Result -activity of tet promoters- '''</font>
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[[Image:Tech_disp_fig1.jpg|450px|thumb|right|figure2-2. Pressure response of Ptet. Ptet activity increased  under 30 MPa]]
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[[Image:Tech Pressure response of tet promoter1.jpg|450px|thumb|right|figure2-2. Pressure response of the tet promoter without repressor protein. Tet promoters' activity increased  under 30 MPa]]
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<div>The result shows that Ptet activity under 30 MPa pressure is about 3 fold stronger than Ptet activity under 0.1 MPa pressure. Therefore, we confirmed that Ptet was induced under 30 MPa pressure.</div><td>
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<div>The result shows that the tet promoter activity under 30 MPa, without repressor protein, is about 3-fold stronger than the tet promoter activity under 0.1 MPa. Therefore, we confirmed that the tet promoter was induced under 30 MPa.</div><td>
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<p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>
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== <font size=5>'''3 Touch display'''</font> ==
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== <font size=5>'''3. Touch display'''</font> ==
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===<font size=3>'''Touch display''' (plan)</font>===
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<font size=3>'''Touch display''' (plan)</font>
[[image:Tech Pressure device2.jpg|right|400px|thumb|figure 3-1-b. Design of touch display]]
[[image:Tech Pressure device2.jpg|right|400px|thumb|figure 3-1-b. Design of touch display]]
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<div>Touch display that we planned has many holes, and <i>E. coli</i> is in these holes.(figure 3-1 a)<div>
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<div>Touch display which we planned has many holes, and <i>E. coli</i> is in these holes.(figure 3-1 a)<div>
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<div>As the first step of creating the touch display,we created basic touch display. figure 3-1 b)</div>
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<div>As the first step of creating the touch display, we created Prototype touch display. figure 3-1 b)</div>
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===<font size=3>'''Basic touch display'''</font>===
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<font size=3>'''Prototype touch display'''</font>
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[[image:Tech_aqulyl2.JPG|right|450px|thumb|figure 3-2.Basic touch display. The display has two kinds of holes and two kinds of covers. ]]
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[[image:Tech_aqulyl2.JPG|right|450px|thumb|figure 3-2. Prototype touch display. The display has two kinds of holes and two kinds of covers. ]]
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<p class=MsoNormal>We created a basic touch display made of acrylic glasses. This touch display has two kinds of holes(show figure 3-2). Each hole contains culture medium and <i>E. coli</i> is cultivated in those holes. One hole (A) can be pressurized, because the hole is covered with only a plastic tape. And water pressure conducts into the hole. The other (B) is not pressurized, because the hole is covered with a block made of acrylic glasses. Water pressure doesn’t conduct into the hole.</font></p>
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<div class=MsoNormal>We created a Prototype touch display made of acrylic glasses. This touch display has two kinds of holes(show figure 3-2). Each hole contains culture medium and <i>E. coli</i> is cultivated in these holes. One hole (A) can be pressurized, because the hole is covered with only a plastic tape. Water pressure conducts into the hole.</div>
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<div>The other (B) is not pressurized, because the hole is covered with a block made of acrylic glasses. Water pressure doesn’t conduct into the hole.</font></div>
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[[image:Tech_aqulyl1.jpg|left|thumb|800px|figure 3-3. Touch display. We pour culture medium into the holes.]]
[[image:Tech_aqulyl1.jpg|left|thumb|800px|figure 3-3. Touch display. We pour culture medium into the holes.]]
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<p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p>
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<p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;</p><p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p>
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===<font size=3>'''How to apply pressure to “touch display”'''</font>===
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<p>Dilute culture medium by 1% by addtion of fresh medium and suitable antibiotic (ampicillin; 50㎍/ml). Next, we pour this culture medium into display's holes with oxygen-saturated Fluorinert (25% volume of medium). We put the display into pressure vessel filled with water (1). Next cap the vessel (2). We apply pressure to the vessel by pressure device (4). We start incubation at 37 degrees for 16h (5).</p></td>
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[[Image:Tech_pressure.jpg|center|800px|thumb|figure 3-4.Protocol for apply pressure to a display.]]
 
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===<font size=3>'''Result ~ E. coli in the touch display ~'''</font>===
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<font size=3>'''Result ~ <i>E. coli</i> in the touch display ~'''</font>
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== <font size=5>'''4 Low pressure-inducible promoter'''</font> ==
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== <font size=5>'''4. Low pressure-inducible promoter'''</font> ==
[[Image:tokyotech2008Previous study - Pressure response of Plac.png|thumb|right|350px|box|Figure 4-1. - Pressure response of Plac]]
[[Image:tokyotech2008Previous study - Pressure response of Plac.png|thumb|right|350px|box|Figure 4-1. - Pressure response of Plac]]
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=== Methods ===
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<font size=3>'''Methods''' </font>
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<gallery widths="400px" heights="280px" >
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<gallery widths="400px" heights="230px" >
Image:Tokyotech2008PCR random mutagenesis.png|Figure 4-2 - PCR random mutagenesis
Image:Tokyotech2008PCR random mutagenesis.png|Figure 4-2 - PCR random mutagenesis
Image:Tokyotech2008Screening scheme with flow cytometer.png|Figure 4-3 - Screening scheme with flow cytometry
Image:Tokyotech2008Screening scheme with flow cytometer.png|Figure 4-3 - Screening scheme with flow cytometry
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We tried to develop a low pressure inducible promoter by PCR random mutagenesis to lac promoter.
We tried to develop a low pressure inducible promoter by PCR random mutagenesis to lac promoter.
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Then we screened an ''E. coli'' library for promoters that are induced under low pressure with flow cytometry.
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Then we screened an ''E. coli'' library, with flow cytometry, for promoters that are induced under low pressure.
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This scheme is based on the ability to separate bacteria with a flow cytometer in response to expression, or lack of expression, of a fluorescent marker.
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This scheme is based on the ability to separate bacteria, with a flow cytometer, in response to expression, or lack of expression, of a fluorescent marker.
*'''Step 1''' - Fluorescent bacteria without repressor protein were collected by a flow cytometer. This sorted pool contains bacteria bearing both constitutive and low pressure-inducible promoter.
*'''Step 1''' - Fluorescent bacteria without repressor protein were collected by a flow cytometer. This sorted pool contains bacteria bearing both constitutive and low pressure-inducible promoter.
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*'''Step 2''' - Constitutive promoter are removed with repressor protein and sorting all non-fluorescent bacteria.
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*'''Step 2''' - This sorted pool contains bacteria bearing both constitutive and pressure-inducible promoter fusions. False positives are removed with repressor protein. All non-fluorescent bacteria are sorted.
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*'''Step 3''' - A final passage through under pressure with repressor protein and sorting for fluorescent bacteria removes false negatives and enriches for bacteria bearing promoter that are low pressure-inducible.
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*'''Step 3''' - A final passage. We sorted bacteria under pressure with repressor protein. Fluorescent bacteria are sorted. False negatives are removed. Therefore bacteria bearing promoter that are low pressure-inducible are isolated.
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=== Results - Sequence and Characterization -===
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<font size=3>'''Results - Sequence and Characterization -''' </font>
We finished step 1.
We finished step 1.
Fluorescent and non-fluorescent bacteria were sorted and we characterized their promoter.
Fluorescent and non-fluorescent bacteria were sorted and we characterized their promoter.
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<gallery widths="430px" heights="240px" >
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Image:Tokyotech2008Dot plot of cell sorting .png|Figure 4-4 - Dot plot of cell sorting
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Image:Tokyotech2008Dot plot of cell sorting .png|figure 4-4. Dot plot of cell sorting
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Image:Tokyotech2008Results of sequencing .png|Figure 4-5 - Results of sequencing
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Image:Tokyotech2008Results of sequencing .png|figure 4-5. Results of sequencing
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We sorted fluorescent (A) and non-fluorescent bacteria (B) with a flow cytometer.
We sorted fluorescent (A) and non-fluorescent bacteria (B) with a flow cytometer.
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Therefore, fluorescent bacteria have  no mutation in CAP binding site, -35 or -10.
Therefore, fluorescent bacteria have  no mutation in CAP binding site, -35 or -10.
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=== Conclusion ===
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We have successfully demonstrated that it is possible to collect promoters desired functions by PCR random mutagenesis and screening with a flow cytometry.
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We have successfully demonstrated that it is possible to collect objective promoter by PCR random mutagenesis and screening with a flow cytometry.
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This results indicate that we can screen low pressure-inducible lac promoter mutant with this methods.
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So we are confident that we can screen low pressure-inducible lac promoter mutant with this methods.
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== <font size=5>'''5 Write/Erase cycle'''</font> ==
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== <font size=5>'''5. Write/Erase cycle'''</font> ==
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[[Image:Write-Erase_cycle.png|thumb|400px|right|figure5-1. Write/Erase cycle]]
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[[Image:Write-Erase_cycle.png|thumb|400px|right|figure 5-1. Write/Erase cycle]]
While we can implement write-function, we want to implement additionally erase-function and memory-function. Erase-function enables us to erase the painted picture, and memory-function enables us to keep the picture after we stop induction. We call these functions "Write/Erase cycle".
While we can implement write-function, we want to implement additionally erase-function and memory-function. Erase-function enables us to erase the painted picture, and memory-function enables us to keep the picture after we stop induction. We call these functions "Write/Erase cycle".
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# '''Write-function'''
# '''Write-function'''
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## 30 MPa pressure activates '''P<sub>lac</sub>'''.
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## '''P<sub>lac</sub>''' is under 30 MPa pressure.
## P<sub>lac</sub> expresses CI and GFP.  
## P<sub>lac</sub> expresses CI and GFP.  
## CI represses P<sub>L</sub> and decreases LacI expression.
## CI represses P<sub>L</sub> and decreases LacI expression.
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=== Mathematical model ===
=== Mathematical model ===
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<!--<gallery widths="200px" heights="150px" perrow="1" align="right" caption="Differential equation models">
 
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Image:Room_pressure_model.png|figure 5-3. Atmospheric pressure model. It is known that n<sub>P<sub>L</sub></sub> = 3.0 from earlier studies
 
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Image:30MPa_pressure_model2.png|figure 5-4. 30 MPa pressure model
 
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We used two differential equation models and we call them 'atmospheric pressure model' and '30MPa pressure model'.
 
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In order to implement rewritable function, we decided to use the difference of nullclines of each system so as to satisfy the following condition
 
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* Converge to high CI concentration state under 30 MPa pressure (writable)
 
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* Bistable under atmospheric pressure (erasable)
 
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[[Image:Desirable_condition.png|700px|thumb|left|figure 5-5. Desirable condition. left:under atmospheric pressure (nullclines of figure 5-2), right:under 30MPa pressure (nullclines of figure 5-4).]]-->
 
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==== Why did we use mathematical model? ====  
==== Why did we use mathematical model? ====  
[[Image:Conditions_for_Write-function.png|thumb|500px|right| figure 5-3. Left If P<sub>L</sub> is not activated or is a bit, write-function is available. Right If P<sub>L</sub>  is activated too much, write-function is not available]]
[[Image:Conditions_for_Write-function.png|thumb|500px|right| figure 5-3. Left If P<sub>L</sub> is not activated or is a bit, write-function is available. Right If P<sub>L</sub>  is activated too much, write-function is not available]]
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As mentioned above, it is known that P<sub>lac</sub> is activated '''94.0'''-fold under 30 MPa while we don't know the increase of P<sub>L</sub> strength under 30 MPa. If P<sub>L</sub> is activated too much, P<sub>lac</sub> activity may be weaker than P<sub>L</sub> activity and we can't implement write-function. So, how much is the range of the increase of P<sub>L</sub> activity under 30 MPa so as to become advantageous to P<sub>lac</sub>? To know this range, we need to use mathematical model.
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As mentioned above, it is known that P<sub>lac</sub> is activated '''94'''-fold under 30 MPa while we didn't know the increase of P<sub>L</sub> strength under 30 MPa. If P<sub>L</sub> is activated too much and P<sub>lac</sub> activity is weaker than P<sub>L</sub> activity, we can't implement write-function. So, how much is the range of the increase of P<sub>L</sub> activity under 30 MPa so as to become advantageous to that of P<sub>lac</sub>? To know this range, we need to use mathematical model.
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<gallery widths = "300px" heights="215px" perrow = "1" align = "right">
<gallery widths = "300px" heights="215px" perrow = "1" align = "right">
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Image:Classical_toggle_switch_model.png| figure. 5-4 Classical toggle switch model
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Image:Classical_toggle_switch_model.png| figure 5-4. Classical toggle switch model
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Image:Transfer_Function.png| figure 5-5. Hill function
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Image:Transfer_Function.png| figure 5-5. Transfer function of P<sub>lac</sub>
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Our mathematical model under atmospheric pressure is equal to a classical toggle switch model shown in figure 5-4. n<sub>CI</sub> is the cooperativity of repression of
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Our mathematical model under 0.1 MPa is equal to a classical toggle switch model shown in figure 5-4. n<sub>CI</sub> is the cooperativity of repression of
the lambda promoter, n<sub>LacI</sub> is the cooperativity of repression of the lac promoter, &alpha;<sub>PL</sub> is the effective rate of LacI synthesis   
the lambda promoter, n<sub>LacI</sub> is the cooperativity of repression of the lac promoter, &alpha;<sub>PL</sub> is the effective rate of LacI synthesis   
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and, &alpha;<sub>Plac</sub> is the effective rate of CI synthesis.
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and &alpha;<sub>Plac</sub> is the effective rate of CI synthesis.
n<sub>CI</sub> and n<sub>LacI</sub> are called "Hill coefficient".
n<sub>CI</sub> and n<sub>LacI</sub> are called "Hill coefficient".
&alpha;<sub>PL</sub> and &alpha;<sub>Plac</sub> depend on strength of promoter-RBS, and are adjustable.
&alpha;<sub>PL</sub> and &alpha;<sub>Plac</sub> depend on strength of promoter-RBS, and are adjustable.
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strength of promoter-RBS which are adjustable. We need to identify value of n<sub>CI</sub> and n<sub>LacI</sub> respectively. But we fortunately know '''n<sub>CI</sub> = 3.0''' (T. Tian et al., 2006). So, we measured fluorescence intensity various IPTG concentration to identify n<sub>LacI</sub>.
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Identifying value of n<sub>CI</sub> and n<sub>LacI</sub> are required for the modeling. But we know '''n<sub>CI</sub> = 3.0''' (T. Tian et al., 2006). So, we measured fluorescence intensity various IPTG concentration to identify n<sub>LacI</sub>.
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By testing how LacI represses the lac promoter, Hill coefficient of lac promoter should be decided. In order to adjust effective concentration of LacI, IPTG was added.
By testing how LacI represses the lac promoter, Hill coefficient of lac promoter should be decided. In order to adjust effective concentration of LacI, IPTG was added.
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GFP fluorescence intensity was enhanced in an IPTG-dose dependent manner. It indicates that the LacI repression was getting weaker by adding IPTG. We formulated Hill function fitting the data shown in figure 5-5, and the characteristics of the lac promoter expressed in Hill function was determined. Finally, we obtained '''n<sub>LacI</sub> = 2.2'''.
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GFP fluorescence intensity was enhanced in an IPTG-dose dependent manner. It indicates that the LacI repression was getting weaker by adding IPTG. The characteristics of the lac promoter were calculated by fitting Hill function to the plots shown in figure 5-5, Finally, we obtained '''n<sub>LacI</sub> = 2.2'''.
''' Conditions for bistability'''
''' Conditions for bistability'''
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We simulated the range of &alpha;<sub>PL</sub> in which a toggle switch model is bistability. Here, we set &alpha;<sub>Plac</sub> = 3.0. The result is below.
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We calculated the range of &alpha;<sub>PL</sub> in which a toggle switch model is bistability. Here, we set &alpha;<sub>Plac</sub> = 3.0. The result is below.
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==== Pressure model ====
==== Pressure model ====
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[[Image:Pressure-inducible_toggle_switch_model.png|thumb|300px|right| figure 5-6. Pressure model]]
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[[Image:Pressure-inducible_toggle_switch_model.png|thumb|300px|right| figure 5-6. Pressure-inducible genetic toggle switch model ]]
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We proposed pressure model which has additional parameters to the classic toggle switch model. These parameters are the increase of activity by pressure (&beta;<sub>(p)Plac</sub> or &beta;<sub>(p)PL</sub>). Under atmospheric pressure (0.1 MPa), &beta;<sub>(0.1)Plac</sub> = 1.0 and &beta;<sub>(0.1)PL</sub> = 1.0. On the other hand, under 30 MPa, &beta;<sub>(30)Plac</sub> = 94 and &beta;<sub>(30)PL</sub> is not known.
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We proposed pressure-inducible genetic toggle switch model which has additional parameters to the classic toggle switch model. These parameters show the increase of activity by pressure (&beta;<sub>(p)Plac</sub> or &beta;<sub>(p)PL</sub>). Under atmospheric pressure (0.1 MPa), &beta;<sub>(0.1)Plac</sub> = 1.0 and &beta;<sub>(0.1)PL</sub> = 1.0. On the other hand, under 30 MPa, &beta;<sub>(30)Plac</sub> = 94 and &beta;<sub>(30)PL</sub> was not known.
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In order to implement write-function, we need the transit of the system from bistability to monostable (P<sub>lac</sub> is stronger than P<sub>L</sub>) by 30 MPa pressure. Therefore, we calculated the range of &beta;<sub>(30)PL</sub> which satisfies the above condition.  
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In order to implement write-function, the transit of the system from bistability to monostable (P<sub>lac</sub> is stronger than P<sub>L</sub>) by 30 MPa pressure is required. Therefore, we calculated the range of &beta;<sub>(30)PL</sub> which satisfies the above conditions.  
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[[Image:PL_pressure_response.png‎|200px|none|thumb|left|figure 5-8. Pressure-response ability of P<sub>L</sub>]]
[[Image:PL_pressure_response.png‎|200px|none|thumb|left|figure 5-8. Pressure-response ability of P<sub>L</sub>]]
We identified '''&beta;<sub>(30)PL</sub> = 1.4''' by our wet experiment under 30MPa pressure (figure 5-6). Therefore, we can implement Write/Erase cycle if we choose an appropriate P<sub>L</sub> - RBS strength.
We identified '''&beta;<sub>(30)PL</sub> = 1.4''' by our wet experiment under 30MPa pressure (figure 5-6). Therefore, we can implement Write/Erase cycle if we choose an appropriate P<sub>L</sub> - RBS strength.
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== <font size=5>'''Our Team'''</font> ==
 
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[[Team:Tokyo_Tech/Home|see more]]
 
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== <font size=5>'''Acknowledgements'''</font> ==
 
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Latest revision as of 05:25, 30 October 2008

Main Protcol Parts Submitted to the Registry Our Team Acknowledgements



Contents

1. Our project

Our project is creation of "Coli Touch"!!

What is "Coli touch"?

Coli Touch” has a pressure sensitive display composed of an E. coli lawn. When you touch its display, touched section is colored.
Next I'll tell you about “Coli Touch” work system. Display of “Coli Touch” contains many E. coli. When you touch this display, pressure applies to E. coli in this display. Pressure applied E. coli expresses GFP.

Why pressure?

Coli Touch” uses pressure as input. Why do we use pressure? Past input methods (small molecules, heat and light) are difficult to induce uniformly. Pressure can induce uniformly.

2. Pressure induction

Introduction

 
Tet promoters is known as a sensitive ones to pressure. (T. Sato et al., 1995)

Construction

figure2-1. We constructed Ptet-GFP and promoter less-GFP.

 
We chose the tet promoter (Ptet) as a pressure-inducible promoter. We constructed two plasmids - one is Ptet-GFP on pSB6. The other is promoter less-GFP on pSB6 as a negative control. We measured activity of tet promoters under 0.1 MPa and 30 MPa without repressor protein.

Result -activity of tet promoters-

figure2-2. Pressure response of the tet promoter without repressor protein. Tet promoters' activity increased under 30 MPa

 
The result shows that the tet promoter activity under 30 MPa, without repressor protein, is about 3-fold stronger than the tet promoter activity under 0.1 MPa. Therefore, we confirmed that the tet promoter was induced under 30 MPa.



          

          

          

          

          

          

          

          

          

          

          

3. Touch display

Touch display (plan)

figure 3-1-b. Design of touch display

 
Touch display which we planned has many holes, and E. coli is in these holes.(figure 3-1 a)
As the first step of creating the touch display, we created Prototype touch display. figure 3-1 b)

 

 

figure 3-1-a. Plan to create touch display. We created two-holes display as the first step.


Prototype touch display

figure 3-2. Prototype touch display. The display has two kinds of holes and two kinds of covers.

 
We created a Prototype touch display made of acrylic glasses. This touch display has two kinds of holes(show figure 3-2). Each hole contains culture medium and E. coli is cultivated in these holes. One hole (A) can be pressurized, because the hole is covered with only a plastic tape. Water pressure conducts into the hole.
The other (B) is not pressurized, because the hole is covered with a block made of acrylic glasses. Water pressure doesn’t conduct into the hole.
 

figure 3-3. Touch display. We pour culture medium into the holes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

          

          


Result ~ E. coli in the touch display ~

 

After incubation, we observed the E. coli by a fluorescence microscope.

 

 

figure 3-5. Images from fluorescence microscope. E. coli on left image is more bright than right one

 
The touch display successfully regulated GFP expression in E. coli !
                     

4. Low pressure-inducible promoter

Figure 4-1. - Pressure response of Plac

It is known that lac promoter is induced under 30 MPa (T. Sato et al., 1995). However, 30 MPa is too high to push with the fingers.
Therefore, we tried to develop low pressure-inducible promoter.











Methods

We tried to develop a low pressure inducible promoter by PCR random mutagenesis to lac promoter. Then we screened an E. coli library, with flow cytometry, for promoters that are induced under low pressure. This scheme is based on the ability to separate bacteria, with a flow cytometer, in response to expression, or lack of expression, of a fluorescent marker.


Results - Sequence and Characterization - We finished step 1. Fluorescent and non-fluorescent bacteria were sorted and we characterized their promoter.

We sorted fluorescent (A) and non-fluorescent bacteria (B) with a flow cytometer. Then, we analyze these base sequences.

Therefore, fluorescent bacteria have no mutation in CAP binding site, -35 or -10.

We have successfully demonstrated that it is possible to collect promoters desired functions by PCR random mutagenesis and screening with a flow cytometry. This results indicate that we can screen low pressure-inducible lac promoter mutant with this methods.

5. Write/Erase cycle

figure 5-1. Write/Erase cycle

While we can implement write-function, we want to implement additionally erase-function and memory-function. Erase-function enables us to erase the painted picture, and memory-function enables us to keep the picture after we stop induction. We call these functions "Write/Erase cycle". In order to implement Write/Erase cycle, we tried to construct genetic toggle switch.

Genetic toggle switch to implement Write/Erase cycle

figure 5-2. Genetic toggle switch
  1. Write-function
    1. Plac is under 30 MPa pressure.
    2. Plac expresses CI and GFP.
    3. CI represses PL and decreases LacI expression.
    4. Low LacI expression increases Plac activity. ⇒ Bright!!
  2. Erase-function
    1. The heat activates PL.
    2. PL expresses LacI.
    3. LacI represses Plac.
    4. Therefore, GFP expression decreases.

Mathematical model

Why did we use mathematical model?

figure 5-3. Left If PL is not activated or is a bit, write-function is available. Right If PL is activated too much, write-function is not available

As mentioned above, it is known that Plac is activated 94-fold under 30 MPa while we didn't know the increase of PL strength under 30 MPa. If PL is activated too much and Plac activity is weaker than PL activity, we can't implement write-function. So, how much is the range of the increase of PL activity under 30 MPa so as to become advantageous to that of Plac? To know this range, we need to use mathematical model.


Classical toggle switch model

Our mathematical model under 0.1 MPa is equal to a classical toggle switch model shown in figure 5-4. nCI is the cooperativity of repression of the lambda promoter, nLacI is the cooperativity of repression of the lac promoter, αPL is the effective rate of LacI synthesis and αPlac is the effective rate of CI synthesis. nCI and nLacI are called "Hill coefficient". αPL and αPlac depend on strength of promoter-RBS, and are adjustable. Identifying value of nCI and nLacI are required for the modeling. But we know nCI = 3.0 (T. Tian et al., 2006). So, we measured fluorescence intensity various IPTG concentration to identify nLacI.


Identification of nLacI

By testing how LacI represses the lac promoter, Hill coefficient of lac promoter should be decided. In order to adjust effective concentration of LacI, IPTG was added.

GFP fluorescence intensity was enhanced in an IPTG-dose dependent manner. It indicates that the LacI repression was getting weaker by adding IPTG. The characteristics of the lac promoter were calculated by fitting Hill function to the plots shown in figure 5-5, Finally, we obtained nLacI = 2.2.


Conditions for bistability

We calculated the range of αPL in which a toggle switch model is bistability. Here, we set αPlac = 3.0. The result is below.


figure 5-5.PL - RBS strength range from 2.4 to 7.8

Pressure model

figure 5-6. Pressure-inducible genetic toggle switch model

We proposed pressure-inducible genetic toggle switch model which has additional parameters to the classic toggle switch model. These parameters show the increase of activity by pressure (β(p)Plac or β(p)PL). Under atmospheric pressure (0.1 MPa), β(0.1)Plac = 1.0 and β(0.1)PL = 1.0. On the other hand, under 30 MPa, β(30)Plac = 94 and β(30)PL was not known.

In order to implement write-function, the transit of the system from bistability to monostable (Plac is stronger than PL) by 30 MPa pressure is required. Therefore, we calculated the range of β(30)PL which satisfies the above conditions.

The feasibility of implementation of Write/Erase cycle

figure 5-7. The domain of appropriate parameters if αPlac = 3.0

According to the result of simulation, we found that we can implement Write/Erase function even if PL is activated 2.5-fold when αPL = 7.8.

figure 5-8. Pressure-response ability of PL

We identified β(30)PL = 1.4 by our wet experiment under 30MPa pressure (figure 5-6). Therefore, we can implement Write/Erase cycle if we choose an appropriate PL - RBS strength.