Living Cell Circuits Could Regrow Organs and Produce Biofuels

Scientists have assembled a kind of organic circuit board for living computers by building logic gates within cells.

It's no secret that computer circuits can process enormous amounts of information — entire industries are built around this core function of technology.

But biologists will tell you that living cells process information too, and their process isn't a simple binary exchange of ones and zeros. Instead, cells deal with multiple complex structures of sugars, proteins, lipids, and DNA. As such, the act of “programming” cells, through genetic engineering, is enormously complex.

But that's okay — scientists like a good challenge.

In research from the University of Washington, published in the journal Nature Communications, synthetic biologists announced a new method for turning organic cells into living computers. By installing the organic equivalent of the digital logic gates used in electronics, scientists can code instructions into the cell so that particular inputs result in desired outputs. Instead of silicon and solder, biologists are using DNA and yeast cells to developing this new kind of organic processor.

In a series of experiments, the UW team built the largest organic “circuit board” constructed to date, including seven logic gates assembled in series or parallel.

Each gate consists of a gene with three programmable chunks of DNA. Two act as inputs, with the third as the output. Using CRISPR technology, the researchers programmed specific proteins to act as molecular gatekeepers, determining whether a particular gate will be active or not.

If a gate is active, it sends a signal that deactivates another gate within the organic circuit, which means scientists can basically “wire” together the gates to create logical programs in the cell.

The new research is a significant step forward for synthetic biology, said senior author and UW electrical engineering professor Eric Klavins.

“Digital logic has been done at a small scale, a few gates, many times over the last decade or so,” Klavins said in an email. “Our paper is the first to produce large circuits built in a eukaryote (yeast), in which transcriptional machinery is considerable more complex.”

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Eurkaryotic cells, like human cells, contain a nucleus and other structures that enable complex behaviors. These are the kinds of cells we'll need to hack for doing those really useful things — like regrow a liver.

“Cells could be reprogrammed to undergo new developmental pathways, to regrow organs, or to develop entirely new ones,” Klavins said. “In such developing tissues, cells have to make complex digital decisions about what genes to express and when, and our technology could be used to control that process.”

The organic circuit board could also be used to produce viable biofuels, which requires importing genes from several different organisms into a hybrid industrial strain, Klavins said.

“Those genes express protein enzymes that each do a particular conversion of one molecule to another, along a metabolic pathway that usually starts with sugar and ends with the fuel,” he said.

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The trick is how to control that conversion process.

“Imported genes are usually not expressed at the proper levels, and control logic that sets those levels, or controls when the pathway turns on during fermentation, is needed,” Klavins said. “Our large scale circuitry could be used to implement that high-level control.”

Such breakthroughs are a ways down the line, however, since we'd need DNA circuits with the power of modern supercomputers. Right now we're dealing with the equivalent of those 1980s make-your-own-computer, mail-order hobbyist kits.

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