New DNA computer stores long-term cellular memory.

The exciting field of biocomputing involves the processing and storing of information in living cells. This discipline is currently being developed with a view to next-generation therapeutics and for capturing events within the body.

In DNA computing, the input is represented using the four-character genetic alphabet, adenine, guanine, cytosine, and thymine, rather than the binary alphabet used by traditional computers. Still, DNA computational technology has only been able to capture and record a limited number of molecular events in the body, meaning they cannot be used over long periods of time.

The development of smart drugs

Now, a study from researchers at MIT programs human and bacterial cells to keep a record of complex molecular events over a long length of time. The team states their DNA-based Ordered Memory and Iteration Network Operator (DOMINO) could one day track the changes which occur from generation to generation as cells differentiate. Similarly, their development could also be used to create sensors capable of detecting, and possibly even treating, diseased cells. The opensource study is published in the journal Molecular Cell.

Previous studies show existing biocomputers have limited recording capacity and are challenging to scale. Recent studies from the group developed a technique able to place new DNA sequences into predetermined locations in the genome in bacterial cells. Consequently, in 2016 they developed a memory storage system based on CRISPR, a genome-editing system responsible for guiding the enzyme to a specific area of the genome.

Using CRISPR to build DNA circuits

Thus, this CRISPR-based process allowed the researchers to insert mutations at specific DNA location. It should be noted, the mutational outcomes were not always predictable and limited the amount of information stored. The current study uses a variant of CRISPR with the ability to precisely edit DNA bases. Accordingly, the DNA was able to store complex memories in living cells, including human cells.

The current study attaches a version of the CRISPR-Cas9 enzyme to a recently developed base editor enzyme. This, in turn, converts the nucleotide cytosine to thymine without breaking the double-stranded DNA.

Results show guide RNA strands, which direct the base editor where to make this switch, are produced only when certain inputs are present in the cell. Data findings show when one of the target inputs is present, the guide RNA leads the base editor either to a stretch of DNA the researchers added to the cell’s nucleus, or to genes found in the cell’s own genome, depending on the application. Thus, measuring the resulting cytosine to thymine mutations determines what the cell has been exposed to.

Recording events in cells

The lab states they used DOMINO to create circuits with the capacity to perform logic calculations, detect the presence of multiple inputs, and record a cascade of events occurring in a certain order. They go on to add their DNA computer can be used to record many events in the life of a cell. This includes exposure to certain chemicals. Additionally, this memory-storage capacity can act as the foundation of complex circuits in which one event triggers another event, such as the production of a fluorescent protein.

The team surmises they have developed a DNA computer extending the utility of molecular recording beyond DNA write-only applications. Moreover, the biotechnology also enables long-term recording and monitoring of in vivo molecular events. For the future, the researchers state these new ‘living sensors’ may one day be able to sense pathogens and toxins in the body.

Source: Massachusetts Institute of Technology  

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