Such circuits could also be used to create a type of circuit known as a digital-to-analog converter. This kind of circuit takes digital inputs for example, the presence or absence of single chemicals and converts them to an analog output, which can be a range of values, such as continuous levels of gene expression.
For example, if the cell has two circuits, each of which expresses GFP at different levels when they are activated by their specific input, those inputs can produce four different analog output levels. Moreover, by measuring how much GFP is produced, the researchers can figure out which of the inputs were present.
That type of circuit could offer better control over the production of cells that generate biofuels, drugs or other useful compounds. Instead of creating circuits that are always on, or using promoters that need continuous inputs to control their output levels, scientists could transiently program the circuit to produce at a certain level. The cells and their progeny would always remember that level, without needing any more information.
Used as environmental sensors, such circuits could also provide very precise long-term memory. "You could have different digital signals you wanted to sense, and just have one analog output that summarizes everything that was happening inside," Lu says.
This platform could also allow scientists to more accurately control the fate of stem cells as they develop into other cell types. Lu is now working on engineering cells to follow sequential development steps, depending on what kinds of inputs they receive from the environment.
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology