Editors' ChoiceSYNTHETIC BIOLOGY

Press pause to fast forward

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Science Translational Medicine  09 Dec 2015:
Vol. 7, Issue 317, pp. 317ec211
DOI: 10.1126/scitranslmed.aad8030

Hit pause on a video and you can scan the screen, analyze the scene, and edit the picture. Hit pause on a cell cycle, and you could one day do the same: A simple and reversible method for arresting the cell cycle at different stages would provide opportunities to genetically manipulate mammalian cells with great efficiency and reproducibility. Current methods to control cell cycle using nutrient deprivation and small-molecule inhibition are cell-type–specific and disrupt other cellular processes. Here, Wei and Smolke present a genetically encoded ribozyme-based method that can control cell cycle by regulating RNA message of key checkpoint proteins.

Wei and Smolke first genetically engineered a human osteosarcoma cell line to individually overexpress known cell cycle regulatory proteins. The assays showed that certain single proteins could inhibit G0/1 or G2/M transition by ~50% in the overall cell population. Optimization of the gene expression construct or coexpression of multiple regulatory proteins showed little to no improvement. After identifying the important protein regulatory nodes, the group then implemented a small molecule–responsive ribozyme switch that could control the RNA transcript for these proteins. (Ribozymes are self-cleaving RNA regulatory elements that can be inserted into the untranslated region of a target gene for transcriptional control.) Exposing the cell culture to the small molecule flipped the ribozyme switch, effectively degrading the RNA for the cell cycle protein target and arresting cells at a particular cell cycle stage. The ribozyme switch was found to be effective and durable for weeks. Crucially, the arrest is also reversible, allowing the cell cycle to restart without the damage caused by previous methods.

Controlling cell cycle in a predictable manner opens up the opportunity to improve the efficiency of genetic engineering, which is dependent on the stage of the cell cycle. Furthermore, arrested cells more stably express transgenes for episomes, allowing for potentially safer gene therapy in human cells without genome integration. However, the methods used by Wei and Smolke were cell type–specific, so further application will require identification of important nodes in each cell type of interest. Nevertheless, arresting cell cycles with ribozyme switches suggests that a temporary pause can put science on fast forward.

K. Y. Wei and Smolke, Engineering dynamic cell cycle control with synthetic small molecule-responsive RNA devices. J. Biol. Eng. 10.1186/s13036-015-0019-7 (2015). [Full Text]

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