Revision as of 23:43, 1 November 2017

RNA Aggregation

In synthetic biology, we are often introducing new pathways to bacteria that do not naturally express them. The novel pathway will produce exotic enzymes and proteins which the host bacteria will not necessarily have the internal environment to organise these macromolecular products, this could be detrimental to the performance of both the pathway and the organism itself. Additionally, depending on the organism used, the activity of the pathway can vary and be difficult to characterise against other models used. Thus, we aim to standardize the microenvironmental activity of different pathways within the cell by localising the associated enzymes/proteins in an RNA based structure, leading to the pathway to act in a predictable way, regardless of the organism.

Fig. 1: A.) Representation of single-stranded RNA that forms the liquid-liquid phase separated-like structure. B.) Images of RNA aggregates formed inside the nucleus of different mutant mammalian cells that express RNA containing either the repeats CUG or CAG

In mammalian cells, RNA containing triplet repeats of nucleotides such as CAGCAGCAGCAG have been observed to aggregate in the nucleus. The properties of the RNA aggregation has been observed to be similar to those seen in liquid-liquid phase separated molecules, which can be visualized as oil droplets in water. The densely compact RNA strands will allow small molecules or substrates to pass through the structure while maintaining a different internal environment. Using this idea, we aimed to express RNA containing repeats in bacterial cells, in order to develop an intracellular scaffold.

In Vivo Scaffolding

Fig. 2: A) A schematic of the construct use to generate RNA aggregates that contain MS2 aptamers. B) The specific binding of FA and FB will form a complete GFP. C) The production of FA with MS2 will will be in competition to either bind with FB or the RNA aggregation.

Fig. 3.

FA-FB System

The FA-FB system is a visualisation method that uses two components of a split GFP, FA and FB, which can bind together to form a complete GFP. Usually, the two components are linked to specific aptamers which bind to their respective domains, allowing the GFP to be present at the site of interest. The FA component is expressed an MS2 aptamer, which is a specific bacteriophage binding site that connects an MS2 binding domain. By expressing the CAG repeat sequence with an MS2 binding domain (fig. 2A), specific binding can occur on the RNA aggregation. Thus, this creates a localization of FA in the cell.

Model Prediction

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FA-FB Results

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Synthesis of CAG Repeats

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Fig. 2: A) The resulting product of the repeat synthesis from random assembly of 10xCAG and 10xCTG nucleotides at initial concentrations of 0μl, 2μl, 3μl and 4μl. B) A schematic representation of the random assembly of the 10xCAG and 10xCTG sequences.

A collection of repeat sequences was built using two oligonucleotides: 10xCAG and 10xCTG. Through testing a variety of oligonucleotide concentrations and testing a different of PCR conditions, a specific protocol was built to synthesise various lenths of DNA containing CAG repeats. The resulting product appeared as a smear, indicating a range of lengths was created, the product was subsequently transformed into a T7 containing vector in order to produce RNA containing CAG repeats.

Centre for Research and Interdisciplinarity (CRI)
Faculty of Medicine Cochin Port-Royal, South wing, 2nd floor
Paris Descartes University
24, rue du Faubourg Saint Jacques
75014 Paris, France

bettencourt.igem2017@gmail.com

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