Part:BBa_K2100041:Experience

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Applications of BBa_K2100041

We experimented with the construct pTAL21 to test the functionality of the promoter in a cascade. This experiment entailed multiple plasmids to be activated: pERE3:TAL21 (500ng), pTAL21:EYFP (170ng), hEF1a:mKate (170ng), hEF1a:Gal4VP16 (170ng), which is approximately a 3:1:1:1 ratio of plasmids.

Our estrogen sensitive promoters respond to increases in E2 levels by producing more of the repressor. The repressors then bind to binding sites in a promoter upstream of fluorescent reporter eYFP. The constitutively active trans-activator Gal4-VP16 sets a large basal eYFP expression when there is no repressor, so that a measurable drop in signal can be observed when repressors are active. Constituvely active hEF1a mKate serves as a transfection marker by which we bin our data.

The first cell line in which we deployed our genetic circuit was ISH, the endometrial epithelial cell line. We had expected eYFP expression to decrease after induction of our promoter - repressor cascades with E2.

[ISH image here]

Blue contours represent the cell population that was left uninduced, green contours represent the cell population that was induced with 5 nM E2.

However, we were unable to resolve a clear fold difference between the uninduced and induced population in the pERE3 and TAL21 cascade. This is probably an artifact of poor transfection in the ISH cell line for this experiment (less than 2 percent transfected after cationic lipid transfection), which leads to erratic jumps in the data after binning by constitutive marker. In the future, we may want to try other modes of transfection for ISH to improve the transfection efficiency.

We next proceeded to deploy this experiment in MCF7. We hypothesized that we were unable to resolve a clear fold difference in our pERE3 - TAL21 cascade transfected into ISH because of the limited functionality of our promoters in the ISH cell line. So, we proceeded to transfect our cells into the MCF7 cell line where we had observed up to a 11 fold difference in the activity of some of our promoters.

[MCF-7 image here]

Blue contours represent the cell population that was left uninduced, green contours represent the cell population that was induced with 5 nM E2.

Similarly, we had expected eYFP expression to decrease after induction of our promoter - repressor cascades with E2. However, we were still unable to resolve a clear fold difference between the uninduced and induced population in the pERE3-TAL21 cascade. Given more time, we would like to explore whether transfecting our entire circuit on one plasmid instead of four separate plasmids would lead to better results.

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