Feb. 11, 2013 Scientists who built a synthetic gene circuit that allowed for the precise tuning of a gene's expression in yeast have now refined this new research tool to work in human cells, according to research published online in Nature Communications.

"Using this circuit, you can turn a gene from completely off to completely on and anywhere between those two extremes in each cell at once. It's a nice tool if you want to know what happens at intermediate levels of gene expression. There has been no such system so far, but now it is available for mammalian cell research," said senior author Gbor Balzsi, Ph.D., associate professor in The University of Texas MD Anderson Cancer Center Department of Systems Biology.

Present options for altering gene expression in human cells are blunt instruments by comparison. Knocking out a gene eliminates its expression completely. Inhibiting it with RNA interference dials it partially down and can affect other genes. Inserting a gene expression vector into cells overexpresses the gene, but it's usually uncontrolled. Commercially available versions can switch a gene on or off, but cannot precisely dial between these extremes.

"For cancer research, the system will allow scientists to test the boundaries of a gene known to confer resistance to a drug in cancer cells by dialing its expression to different levels and treating the cells with the drug," said first author Dmitry Nevozhay, M.D. Ph.D., instructor in Systems Biology.

"Likewise, such a system would allow personalized gene therapy, by precisely tuning the therapeutic gene level expression depending on disease progression and the patient's need," Nevozhay said.

In microbial or yeast biology research scientists have started to understand and manipulate gene function quantitatively, almost like we understand electronic circuits, Balzsi said. "This makes research in those areas more amenable to engineering and mathematical characterization, -- but that's not true for human cells, and part of the problem is that tools that tune gene expression have been lacking."

A step-by-step guide for others to build mammalian synthetic gene circuits By refining their circuit to work in a human breast cancer cell line, the team demonstrated that their approach can be used in mammalian cells while offering a step-by-step guide that other researchers could follow to build other synthetic circuits for use with other genes.

"With all of our steps reported, if someone wants to build another type of gene expression switch, or oscillator, they could build the circuit in fast-growing yeast cells, where it can be engineered and optimized quickly and reliably," Balzsi said. "Once you know it works in yeast, you know the steps to make it function in human cells. This process is similar to extensive testing of NASA's space operations on Earth before actually carrying them out in space."

Synthetic biologists apply engineering principles to design and build new biological systems for predefined purposes.

In yeast, Balzsi and colleagues synthesized a gene circuit designed to control the level of gene expression precisely using the tetracycline repressor.

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Synthetic circuit allows dialing gene expression up or down in human cells

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