IGEM:Imperial/2010/Cell state indicators
Cell State Reporters
Monitoring Cell Activity might be very useful for scientists in many situations. We propose the use of Cell State Reporters to quickly give visual information of the activities or phase the cells are undergoing which could be achieved by using elements that control expression of state specific genes. This might help to maintain a healthy population and to determine whether population grows anaerobically or aerobically. Furthermore it could be used as a warning signal when cells undergo undesired/stressful phases and to examine if the cells grow in synchrony. Many different regulon systems could potentially exploited for this purpose including without limitation:
- Ntr and Nif system that detect ammonia limitation,
- Arc and Fnr system that detect anaerobic conditions,
- the SOS and response to UV light,
- sporulation in response to starvation and the heat shock response.
Use of system specific promoter, enhancer or repressor elements could be used to create a system that gives feed back in form of different fluorescent proteins to the degree to which the system is activated and by extension about the environment the cell is in.
Control of anaerobic respiration
The Arc system is a two component system consisting of a membrane bound sensor kinase (ArcB) and a response regulator (ArcA). ArcB is activated by changes of the quinol/quinone ratio and autophosphorylates. It then phosphorylates ArcA that represses genes involved in aerobic metabolism such as Citrate synthase, α-KGDH, Pyr DH, Lac DH, cyt bo and SDH but also upregulates cyt bd.
- Malpica et al., 2006. Signaling by the Arc two-component system provides a link between the redox state of the quinone pool and gene expression. Antioxidants and Redox Signalling, 8, 781-795
- Iuchi S & Lin EC. 1988. arcA (dye), a global regulatory gene in Escherichia coli mediating repression of enzymes in aerobic pathways. Proc Natl Acad Sci USA 85: 1888–1892,
The Fnr system makes use of the Fnr proteins that contains a iron sulphure cluster. Depeding on the redox potential of the cytoplasm and therefore the presence or absence of oxygen these can undergo changes. In the absense of oxygen this allows Fnr proteins to dimerise and acts as transcription regulators. It activates Fumarate reductase, NO3-reductase, NO2- reductase, DMSO reductase, FDH reductase and Pyr Formate lyase. It represses SDH, cyt bd, cyt bo and the fnr gene itself.
Cell State as switch for logic gate
The switch of cell state and the subsequent activation of a reporter or activator gene could be used to act as switch between different types of logic gate allowing us to give different, but predictable and programed, outputs from just one input (change in cell state). By creating a different environment we overcome repression of one protein by another thus causing a switch in the function of the logic gate.
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