Genetic circuits can be
isolated within individual synthetic "cells," preventing them from
disrupting each other, demonstrated MIT researchers. The scientists can also control communication
between these cells, allowing for circuits or their products to be
combined at specific times.
This approach could allow researchers to design circuits that
manufacture complex products or act as sensors that respond to changes
in their environment, among other applications.
‘Encapsulating molecular components in artificial membranes offers more flexibility in designing genetic circuits, revealed MIT researchers.’
Synthetic biology allows scientists to design genetic circuits that
can be placed in cells, giving them new functions such as producing
drugs or other useful molecules. However, as these circuits become more
complex, the genetic components can interfere with each other, making it
difficult to achieve more complicated functions.
"It's a way of having the power of multicomponent genetic cascades,
along with the ability to build walls between them so they won't have
cross-talk. They won't interfere with each other in the way they would
if they were all put into a single cell or into a beaker," says Edward
Boyden, an associate professor of biological engineering and brain and
cognitive sciences at MIT. Boyden is also a member of MIT's Media Lab
and McGovern Institute for Brain Research, and an HHMI-Simons Faculty
Boyden is the senior author of a paper describing this technique in Nature Chemistry
The paper's lead authors are former MIT postdoc Kate Adamala, who is
now an assistant professor at the University of Minnesota, and former
MIT grad student Daniel Martin-Alarcon. Katriona Guthrie-Honea, a former
MIT research assistant, is also an author of the paper.
The MIT team encapsulated their genetic circuits in droplets known
as liposomes, which have a fatty membrane similar to cell membranes.
These synthetic cells are not alive but are equipped with much of the
cellular machinery necessary to read DNA and manufacture proteins.
By segregating circuits within their own liposomes, the researchers
are able to create separate circuit subroutines that could not run in
the same container at the same time, but can run in parallel to each
other, communicating in controlled ways. This approach also allows
scientists to repurpose the same genetic tools, including genes and
transcription factors (proteins that turn genes on or off), to do
different tasks within a network.
"If you separate circuits into two different liposomes, you could
have one tool doing one job in one liposome, and the same tool doing a
different job in the other liposome," Martin-Alarcon says. "It expands
the number of things that you can do with the same building blocks."
This approach also enables communication between circuits from different types of organisms, such as bacteria and mammals.
As a demonstration, the researchers created a circuit that uses
bacterial genetic parts to respond to a molecule known as theophylline, a
drug similar to caffeine. When this molecule is present, it triggers
another molecule known as doxycycline to leave the liposome and enter
another set of liposomes containing a mammalian genetic circuit. In
those liposomes, doxycycline activates a genetic cascade that produces
luciferase, a protein that generates light.
Using a modified version of this approach, scientists could create
circuits that work together to produce biological therapeutics such as
antibodies, after sensing a particular molecule emitted by a brain cell
or other cell.
"If you think of the bacterial circuit as encoding a computer
program, and the mammalian circuit is encoding the factory, you could
combine the computer code of the bacterial circuit and the factory of
the mammalian circuit into a unique hybrid system," Boyden says.
The researchers also designed liposomes that can fuse with each
other in a controlled way. To do that, they programmed the cells with
proteins called SNAREs, which insert themselves into the cell membrane.
There, they bind to corresponding SNAREs found on surfaces of other
liposomes, causing the synthetic cells to fuse. The timing of this
fusion can be controlled to bring together liposomes that produce
different molecules. When the cells fuse, these molecules are combined
to generate a final product.
The researchers believe this approach could be used for nearly any
application that synthetic biologists are already working on. It could
also allow scientists to pursue potentially useful applications that
have been tried before but abandoned because the genetic circuits
interfered with each other too much.
"The way that we wrote this paper was not oriented toward just one
application," Boyden says. "The basic question is: Can you make these
circuits more modular? If you have everything mishmashed together in the
cell, but you find out that the circuits are incompatible or toxic,
then putting walls between those reactions and giving them the ability
to communicate with each other could be very useful."
Another possible application for this approach is to help scientists
explore how the earliest cells may have evolved billions of years ago.
By engineering simple circuits into liposomes, researchers could study
how cells might have evolved the ability to sense their environment,
respond to stimuli, and reproduce.
"This system can be used to model the behavior and properties of the
earliest organisms on Earth, as well as help establish the physical
boundaries of Earth-type life for the search of life elsewhere in the
solar system and beyond," Adamala says.