Researchers have developed a new genetic editing enzyme system to record cellular events inside bacterial and mammalian cells.
Scientists from Harvard University in Cambridge, Massachusetts developed a molecular biology tool called CAMERA that can record the reaction of bacterial and mammalian cells to various environmental stimuli. The technology is based on CRISPR-Cas9, a DNA editing tool.
CRISPR-Cas9 is often used as a set of molecular scissors to cut specific areas of double-stranded DNA. Scientists add a “guide RNA,” a small stretch of nucleic acids that enables the CRISPR-Cas9 complex to target a specific DNA sequence, and cut it using the Cas9 enzyme.
The idea is that researchers can add a pair of short circular DNA fragments containing marker genes with different DNA sequences into the cells. These DNA fragments don’t disturb the host cell unless they contain the code for a gene that does something. Then, the researchers add a midified version of the CRISPR/Cas9 tool that can be activated by a specific stimulus. This might be a flashing light at a specific wave length, or it could be a chemical added to the dishes or even the product of a gene encoded by the host cell. When the stimulus is applied, the CRISPR/Cas9 activates and cuts a chunk out of one of the two plasmids. The cells can then be collected in a test tube and mashed up. The researchers then extract the circular DNA fragments and measure the relative amounts of the two different types. That can be used as an indirect measure of how many cells reacted to the stimulus or how strong the stimulus was.
By combining the precise cutting ability of CRISPR-Cas9 with an antibiotic resistance gene and two types of circular DNA (plasmids), researchers were able to test how long bacterial cells were exposed to an antibiotic. They accomplished this by exposing CAMERA-equipped cells to the antibiotic and then examining the change in the ratios of the two plasmids inside the cells. Other CAMERA systems were designed to respond to specific cell signals and other environmental stimuli such as nutrients, viruses, and light.
Two key characteristics of the CAMERA system are that only 10-100 cells are needed to record reliable information and that multiple cellular events can be recorded, erased, and re-recorded. Similar to flight data recorders, CAMERA systems function as “cell data recorders.”
The power of this technology has enormous potential for helping researchers understand all kinds of processes including aging, the occurrence of cancer, and embryonic development. Scientists in the field are excited about the future applications of CAMERA.
Written by Cindi A. Hoover, Ph.D.
Reference: Tang, D.R. Liu, Science. 10.1126/science.aap8992 (2018). http://science.sciencemag.org/content/359/6377/728.full.
