One defining goal of synthetic biology is the development of engineering-based
approaches that enable the construction of gene-regulatory networks according
to "design specs" generated from computational modeling. Such an approach
provides a systematic framework for exploring how a given regulatory network
generates a particular phenotypic behavior. This approach has resulted in the
development of several fundamental gene circuits, such as toggle switches and 
oscillators, and these have been applied in novel contexts such as triggered 
biofilm development and cellular population control. In this talk, I will 
describe an engineered genetic oscillator in Escherichia coli that is fast, 
robust, and persistent, with tunable oscillatory periods as low as 20 minutes. 
The oscillator was designed using a previously modeled network architecture 
comprising linked positive and negative feedback loops, and adapts components 
from the E. coli genome. Using a microfluidic platform tailored for single-cell 
microscopy, we precisely control environmental conditions, monitor oscillations 
in individual cells through multiple cycles, and observe the desynchronization 
that occurs over time. The circuit can be synchronized by the initial addition 
of inducer to a batch culture, allowing high-throughput measurement of oscillatory 
properties by "timelapse" flow cytometry. To further explore the dynamics of the 
oscillator, we derived computational models that accurately describe the behavior 
of the system. We found that dimer- and tetramerization of the transcription 
factors as well as the stochastic nature of gene expression can contribute to the 
robustness of this oscillator.  The underlying methodology highlights the utility 
of engineering-based methods in the exploration of gene regulatory networks.