Seminar: Cell-free systems for gene expression

Our speaker this evening is Vincent Noireaux from the University of Minnesota. Vincent is a leading researcher and developer of cell-free systems, TXTL (transcription-translation), where cell extract is used to express RNA and proteins from DNA. Vincent deserves special acknowledgement…he generated about 1000 tubes of TXTL cell extract for the CSH Synthetic Biology course!

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Vincent’s group has advanced cell-free systems beyond the earlier founding systems, which could produce some protein and RNA but could not support complex gene interactions and cascades. These systems also perturbed degradation, which is just as important for a system’s function as production. His group’s system carefully formulated TXTL to make it possible to observe gene expression and regulation dynamics over longer time scales. A large proportion of the cell-free solution is a precisely defined solution (called “energy mix”) with a smaller portion consisting of cell cytoplasm extracted from E. coli. The final consistency is close to water. This special formulation was the first to enable characterization of not just basic expression, but dynamic genetic circuits (and gates, bistable switches, feed forward loops, and negative feedback loops) in vitro.

This represents a large advance for synthetic biology. Simple, detectable functions of protein, RNA, and gene circuits (on circular or linear DNA) can be tested in a solution, bypassing the requirement for the components to be delivered past a cell membrane/ wall. Furthermore, the system is not subject to disruption by cell division. The system is highly scalable, since small-volume reactions can be set up in microplates…output can be scanned on a microplate reader.

Vincent concluded with very exciting new results from work to operate TXTL within liposomes, small lipid-based bubbles that act almost as synthetic cells, but they do not divide. This advance has exciting implications for scanning millions of unique gene circuit variants in a matter of minutes, perhaps via flow cytometry.

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