Latest revision as of 20:02, 19 October 2016

Experimental Strategy

We designed a bring DNA closer tool (BDC tool) and a visualization tool, as mentioned perviously. In order to characterize our tools, we set up the experimental strategy explained bellow.

Characterization strategy

Tripartite Split-GFP and FRB*-FKBP12 dimerization systems

First, we designed two biobricks to test the FRB*/FKBP12 interaction and the tripartite GFP system. FRB* was fused with one subunit of the gene encoding the GFP (GFP 11) and FKBP12 was fused with another subunit (GFP10) [Fig1]. Then, we also put the gene encoding the last subunit (GFP 1-9) in the plasmid pSB1C3 to form the tripartite GFP [Fig2].

Figure 1: Tripartite split-GFP and FRB*/FKBP12 functional assessment. Biobricks corresponding to intermediate characterization. FRB* is fused with GFP11 and FKBP12 is fused with GFP10.

In order to test the system, we built a plasmid containing three biobricks to express the full system [Fig2]. Then we transformed it in E. coli to assess the system. The system would be tested by measuring GFP fluorescence level under two different conditions [Fig1]: a growth medium containing rapalog (rapamycin analog) and a growth medium without it. We also planed to test it in bacteria containing just two parts (FRB-GFP11 and FKBP12-GFP10) instead of three (so without GFP1-9).

Figure 2: Biobrick design containing all the parts to characterize tripartite split-GFP and FRB*/FKBP12. All our biobricks in one plasmid and no interference.

This construction would give us the first results, validate the functionality of the tripartite GFP and the dimerization of FRB* and FKBP12.

Assessment of the minimal distance to have fluorescence

One of the goals of our project is to assess the system composed of the BDC tool and the tripartite split-GFP. To evaluate the effect of the bring DNA closer tool, we have to know the minimal distance needed to observe fluorescence emission.

This question was also the core of our model, which answers the question: What is the optimal distance between the two dCas9s to observe fluorescence?

This question is essential because the distance between the dCas9s may cause major problems. First, steric hindrance and dCas9 footprint may avoid GFP assembling if we target sequences that are too close. Secondly, the proteins size could prevent the GFP parts from assembling if they are too far away. As a result, fluorescence emission would be detected only if the proteins, as well as the DNA regions, are at a precise range of distance.

To experimentally assess such distance, we decided to design different plasmids containing the visualization target sequences separated from each other by different number of base pairs [Fig3]. To do so, we designed specific primers to carry out reverse PCR and obtain, from a plasmid in which the target sequences are distant by 1kB, different plasmids where the number of base pairs between the target sequences is reduced. This plasmid was thought to be expressed with the plasmid pSB1C3 containing the BioBricks 3, 4 and 5 (cf design page). The target sequences would have been separated by:

1kB
500bp
150bp
75bp
50bp

T--Paris Saclay--distance assessment.jpeg

Figure 3: Plasmid design to assess the minimal distance needed to have GFP fluorescence and fully characterize the tripartite split-GFP. It would be expressed with the visualization tool BioBrick. The different RT-PCRs would allow us to have different distances between the two target sequences.

Assessment of the DNA regions brought closer

In order to test our BDC tool, all the biobricks previously quoted in the design page should be expressed in E. coli, as well as all the sgRNAs (corresponding to the target sequences and their cognate dCas9s). Later, the team would measure GFP fluorescence levels in growth medium with or without rapalog. The emission of any fluorescence by the tripartite split-GFP would validate our BDC tool [Fig4] as it would mean the two target sequences are close.

T--Paris Saclay--BDCtool characterization.jpeg

T--Paris Saclay--BDCtool characterization continuation.jpeg

Figure 4: BDC tool characterization by the visualization tool mechanism. Using both tools together.

Gene expression tests

In order to test a possible influence of the spatial proximity in gene expression, we would test the expression of two different reporter genes. With the aim of having more accurate variation measurements, we should use enzymes such as luciferase or beta-galactosidase.

@@ Line 1: / Line 1: @@
-{{Team:Paris_Saclay/project_header}}
+{{Team:Paris_Saclay/project_header|titre=Experimental Strategy}}
+<html><style>header{background-image: url("https://static.igem.org/mediawiki/2016/8/8f/T--Paris_Saclay--banniere_project.jpg");}
+</style></html>
-The project aim to study how bacterial (e.coli) DNA organization can influence gene expression. In order to answer our question, the team decide to create a new tool based on CRISPR-Cas9 to bring together two distant DNA regions. This new tool is expected to assess the effect of DNA structure on gene expression. As a results, we have designed a linking tool and a visualization tool.
+We designed a bring DNA closer tool (BDC tool) and a visualization tool, as mentioned [[Team:Paris_Saclay/Design#design|perviously]]. In order to characterize our tools, we set up the experimental strategy explained bellow.
-Here, we will expose you our experimental strategy, as well as, the biobricks we have designed to do so.
+=Characterization strategy=
-=Linking tool construction=
+==Tripartite Split-GFP and FRB*-FKBP12 dimerization systems==
-=Visualization tool construction=
+First, we designed two biobricks to test the FRB*/FKBP12 interaction and the tripartite GFP system. FRB* was fused with one subunit of the gene encoding the GFP (GFP 11) and FKBP12 was fused with another subunit (GFP10) '''[Fig1]'''. Then, we also put the gene encoding the last subunit (GFP 1-9) in the plasmid pSB1C3 to form the tripartite GFP '''[Fig2]'''.
-Every system need an efficient control, as a result, a new part of the project has been setting up and the team has designed the visualization tool.
+[[Image:Paris_Saclay--design4.png|frameless|upright=2.5|center|]]
+<center>'''Figure 1''': Tripartite split-GFP and FRB*/FKBP12 functional assessment. ''Biobricks corresponding to intermediate characterization. FRB* is fused with GFP11 and FKBP12 is fused with GFP10.''</center>
-To build this new tool, two other ortholog nuclease function deficient Cas9s (dCas9s) : N.meningitidis and S.thermophilus, will be fused to fluorescent proteins.
-We also decide to use dCas9 system for this tool in order to have detection of a accurate and unique sequence in the genome.
+In order to test the system, we built a plasmid containing three biobricks to express the full system '''[Fig2]'''. Then we transformed it in ''E. coli'' to assess the system. The system would be tested by measuring GFP fluorescence level under two different conditions '''[Fig1]''': a growth medium containing rapalog (rapamycin analog) and a growth medium without it. We also planed to test it in bacteria containing just two parts (FRB-GFP11 and FKBP12-GFP10) instead of three (so without GFP1-9).
-It will be fulfilling with a new and unreleased in the iGEM competition tripartite slip-GFP.
-The tripartit split-GFP is composed of two twenty amino-acids long GFP tags (GFP10 and GFP11) and a third complementary subsection (GFP1-9). The tags will be fused to the two dCas9 previously quoted. A functional GFP will be achieved when the tools would be close enought to allow the three slip-GFP parts reunion and the fluorescence emission.
-This fluorescence system avoids poor folding and/or self-assembly background fluorescence. With this system, only two sgRNAs associate with their dCas9s fused to their specific GFP tags will be necessary instead of nearly 30 with mundane GFP due to background fluorescence.
+[[Image:Paris_Saclay--design5.png|frameless|upright=2.5|center|]]
+<center>'''Figure 2''': Biobrick design containing all the parts to characterize tripartite split-GFP and FRB*/FKBP12. ''All our biobricks in one plasmid and no interference.''</center>
-The team has designed three biobricks to achieve this part of the project.
-* N.meningitidis fused to GFP-10 expressed by a constitutive promoter, a RBS and a double terminator
-* S.thermophilus fused to GFP-11 expressed by a constitutive promoter, a RBS and a double terminator
-* The third part of the GFP 1-9 expressed by a constitutive promoter, a RBS and a double terminator
+This construction would give us the first results, validate the functionality of the tripartite GFP and the dimerization of FRB* and FKBP12.
-[[File:T--Paris_Saclay--visualization_biobricks.jpeg|500px|thumb|center|]]
+==Assessment of the minimal distance to have fluorescence==
-Then, the team has considered to establish a composite biobrick composed of the three biobricks in the same pSB1C3 plasmid.
+One of the goals of our project is to assess the system composed of the BDC tool and the tripartite split-GFP. To evaluate the effect of the bring DNA closer tool, we have to know the minimal distance needed to observe fluorescence emission.
-[[File:T--Paris_Saclay--composite_visualization_biobrick.jpeg|500px|thumb|center|]]
+This question was also the core of our [[Team:Paris_Saclay/Model#modelisation|model]], which answers the question: ''What is the optimal distance between the two dCas9s to observe fluorescence?''
-=Characterization strategy=
+This question is essential because the distance between the dCas9s may cause major problems. First, steric hindrance and dCas9 footprint may avoid GFP assembling if we target sequences that are too close. Secondly, the proteins size could prevent the GFP parts from assembling if they are too far away. As a result, fluorescence emission would be detected only if the proteins, as well as the DNA regions, are at a precise range of distance.
+To experimentally assess such distance, we decided to design different plasmids containing the visualization target sequences separated from each other by different number of base pairs '''[Fig3]'''. To do so, we designed specific primers to carry out reverse PCR and obtain, from a plasmid in which the target sequences are distant by 1kB, different plasmids where the number of base pairs between the target sequences is reduced.
+This plasmid was thought to be expressed with the plasmid pSB1C3 containing the BioBricks 3, 4 and 5 (cf [[Team:Paris_Saclay/Design#design|design]] page).
+The target sequences would have been separated by:
+*1kB
+*500bp
+*150bp
+*75bp
+*50bp
+[[File:T--Paris_Saclay--distance_assessment.jpeg|upright=2.7|frameless|center|]]
+<center>'''Figure 3''': Plasmid design to assess the minimal distance needed to have GFP fluorescence and fully characterize the tripartite split-GFP. ''It would be expressed with the visualization tool BioBrick. The different RT-PCRs would allow us to have different distances between the two target sequences.''</center>
-=====Tripartit Split-GFP and FRB/FKBP12 dimerization systems=====
+==Assessment of the DNA regions brought closer==
-=====Assessment of the minimal distance to have fluorescence=====
+In order to test our BDC tool, all the biobricks previously quoted in the [[Team:Paris_Saclay/Design#design|design]] page should be expressed in ''E. coli'', as well as all the sgRNAs (corresponding to the target sequences and their cognate dCas9s). Later, the team would measure GFP fluorescence levels in growth medium with or without rapalog. The emission of any fluorescence by the tripartite split-GFP would validate our BDC tool '''[Fig4]''' as it would mean the two target sequences are close.
-[[File:T--Paris_Saclay--distance_assessment.jpeg|500px|thumb|center|]]
+[[File:T--Paris_Saclay--BDCtool_characterization.jpeg|frameless|center|upright=2.5|]]
+[[File:T--Paris_Saclay--BDCtool_characterization_continuation.jpeg|frameless|center|upright=2.5|]]
+<center>'''Figure 4''': BDC tool characterization by the visualization tool mechanism. ''Using both tools together.''</center>
-=====Assessment of the DNA regions brought closer=====
+=Gene expression tests=
-=====Gene expression tests=====
+In order to test a possible influence of the spatial proximity in gene expression, we would test the expression of two different reporter genes. With the aim of having more accurate variation measurements, we should use enzymes such as luciferase or beta-galactosidase.
-{{Team:Paris_Saclay/footer}}
+{{Team:Paris_Saclay/project_footer}}

Difference between revisions of "Team:Paris Saclay/Strategy"