Reconstitution of an ultradian oscillator in mammalian cells by a synthetic biology approach

Mammalian cells can encode information by periodic expression of genes. A typical example are the ultradian oscillations (i.e. less than 24 hrs) of Hes1, an effector gene of the mammalian Notch-Delta pathway, involved in several developmental process, such as, the cell fate decision of many kind of stem cell. Therefore, I first quantitatively characterized the cis regulatory element (promoter,3'UTR) of Hes1 gene. Then, guided by the “build it to understand it” principle, I evaluated if the delayed negative feedback is sufficient to give sustained Hes1 oscillations. For this purpose, I reconstituted the Hes1 oscillator in Chinese Hamster Ovary cells (CHO). Than by substituting the natural promoter of Hes1 gene with synthetic analogs we built a synthetic oscillator In conclusion, I shown by real time PCR that the Hes1 promoter is well described by a highly cooperativity Hill's function (n=7). Moreover, for the first time we demonstrated that the 3'UTR is the sequence responsible for the rapid Hes1 mRNA degradation. Finally, we get some evidences that the synthetic oscillator that we built in CHO cells, based on a delayed negative feedback loop, is able to generate periodic expression of Hes1 mRNA.