Monday, May 17, 2010

Directed evolution using engineered cells

Directed evolution of cells is generally done by setting up a screening process. An example is a binding assay for evolving cell surface receptors.

It is very difficult to build screening procedures that select for functions. However, it might be possible to engineer "killer" cells that attack cells with particular types of behaviors. Thus the killer cells provide the screening process. And why limit to a single type of killer cell.. of course, the killer cells should not evolve (might be an issue)

Imagine this scenario: a population of cells evolving in an environment with populations of 3 or 4 different types of killer cells. Each killer cell targets a particular type of behavior. Further, another population of "helper" cells excrete specific nutrients in response to particular behaviors. The target population of cells should evolve to avoid specific functions that are targeted by the killer cells and acquire specific functions targeted by the helper cells. Due to the existence of multiple criteria, the evolution might be more gradual as well.

Signaling - specifity and decoding

Lets consider wireless signals. The signals themselves travel in all directions, so there is no specificity. The frequency provides the sender-receiver specificity. The signal pattern contains information that the receiver can decode, i.e. the receiver must expect a specific type of pattern.

Comparing the general idea to biological signaling... the specificity usually comes from binding affinity, so that aspect of signaling is clear. Now for decoding the information. A pathway probably has multiple molecules serving as signal carriers. The pattern of concentrations of those input molecules *might* serve as the encoded information that the receiver, i.e. the pathway, is able to decode. The pathway then sends a new set of molecules as output signals . Note that this results in a conversion of signal carrier, which is analogous to the wireless signaling analogy where the wireless signal is decoded into some other form such as digital signals.