| The human circadian rhythm drives many important processes in the body in accordance with the sleep/wake cycle. A characteristic of this biological clock is the periodic oscillation of gene expression. Current parts in the Registry designed to regulate periodic oscillations of gene expression have shown limited success.
Here we demonstrate a biological clock being standardised as a set of BioBrick parts. Our network is controlled by an engineered promoter, Plac/ara, which features both an activator and a repressor domain. This controls the production of downstream genes to activate other inducible promoters, pBAD and GlnAp2, eventually leading to the production of a repressor protein, lacI, which inhibits Plac/ara, resulting in oscillatory expression. This project shows the feasibility of standardising the biological clock in E. coli and grounds further development for applications in regulated drug/hormone delivery and ion channel control. | 
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The project has been split into categories:
Together, this forms the UQ-Australia project for the 2011 iGEM.
In humans, the circadian rhythm is controlled by several core genes that operate via a series of feedback loops (Figure 1). A transcription–translation negative-feedback loop powers the system, with a delay between the transcription of these genes and the negative feedback being a key factor that allows the system to oscillate [1]. A 'master clock' located in the Suprachiasmatic Nucleus coordinates the timing of the rhythm, but external factors such as light exposure play a large role in regulating the exact
Figure 1: The gene network responsible for establishing the circadian rhythm in humans [1]
There has been much effort put into reconstructing and determining the exact nature of this system, as the impact the circadian rhythm has on our lifestyle and cellular processes are still not very well understood. In particular, it is believed the circadian rhythm could exert an effect on everything from body temperature, feeding behaviour and appetite, hormone secretion and metabolism, glucose homeostasis, and cell-cycle progression [2].
Consequently, there have been a number of efforts to reconstruct this clock in a mammalian system for further study. In particular, both Hong et al. [3] and Tigges et al. [4] utilize the inducible tTa system to drive the expression and oscillation of genes in their synthetic networks.
It was our initial plan to construct a similar oscillatory system ourselves using standardized parts which could be added to the registry and then utilized by other iGEM teams working in mammalian cells. Such as system could be 'plugged in' to any number of different outputs and would allow for the timely and regular expression of the genes it drives. However, we encountered a number of issues around the intellectual property protecting of certain elements we wanted to use and so decided to switch to a simpler system in E. coli.
Details of this is on the Modelling page.
Details of this is on the Safety page.
The Human Practices section is on the Human Practices
[1] Gallego, M & Virshup, DM 2007. "Post-translational modifications regulate the ticking of the circadian clock", Molecular Cell Biology, vol. 8, pp. 139-148.
[2] Takahashi, JS, Hong, HK, Ko, CH & McDearmon, EL 2008. "The genetics of mammalian circadian order and disorder: implications for physiology and disease", Genetics, vol. 9, pp. 764-775.
[3] Hong, HK, Chong, JL, Song, W, Song, EJ & Jyawook, AA et al. 2007. "Inducible and reversible Clock gene expression in brain using the tTa system for the study of circadian behaviour", PLoS Genetics, vol. 3, no. 2, 324-338.
[4] Tigges, M, Marques-Lago, TT, Stelling, J & Fusseneger, M 2009. "A tunable synthetic mammalian oscillator", Nature, vol. 457, pp. 309-312.
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