Biology Reference
In-Depth Information
culture systems that have been provided with a simple gradient. Cells could, for example, be
made to aggregate only at the position of the 'white' stripe of the French Flag, or alternatively
to become randomly motile there so that the 'white' area always has a lower cell density, as
cells move randomly until they come to rest back in a red or blue area. The effectiveness of
this simple programmed avoidance mechanism might be increased further by reciprocal
control of motility and adhesion, so that cells either stick together (on the red and blue stripes)
or move randomly without sticking (on the white stripe).
An alternative, more self-organizing, system might be constructed by placing the recip-
rocal expression of cell adhesion and motility proteins under the control of an autocrine
secretedmolecule. A solitary cell would experience only a low concentration of this molecule,
as it diffuses away into bulk culture medium, and would be in its adhesive state. As it multi-
plied it would therefore make a clump of cells. Once the clump grew large, the concentration
of the autocrine molecule would rise inside it and cells would change to a motile state, scat-
tering. Alone again, they would become adhesive and begin a new colony. In effect, this
would be an elementary artificial life cycle.
12
For the system to work properly it would
need an element of hysteresis so that the dispersing cells did not flip back to adhesion as
soon as they had their first taste of free medium: sensing systems that show this characteristic
have already been engineered, at least in bacteria.
26
Systems like the one above have not yet been built
d
currently the very young field of
synthetic biology is still at the stage of building the basic genetic modules that will drive
elementary morphogenetic events. The ideas has been covered briefly in this topic because
of the author's belief that it will grow to be an important additional tool for basic research
in the very near future. Building synthetic systems that 'should' develop a particular way
will frequently result in failure. From a scientific point of view, such 'failure' will be valuable
because it will highlight areas where we do not understand morphogenesis as well as we
think we do. Discovering gaps in knowledge is one of the most important drivers of scientific
progress.
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