CRISPR/Cas with switch
The CRISPR/Cas9 genome editing technology developed less than ten years ago has become a real breakthrough in genetics. The CRISPR/Cas9 complex consists of two parts: Cas9, a gene-editing protein, and guide RNA (gRNA), which directs Cas9 to the gene selected for editing. This scheme of work is somewhat similar to scissors.
Similarly, the immune system of bacteria works in response to a collision with viruses. Depending on the final goal, different protein variants can be used, but Cas9 has proven itself to be the most easily programmable enzyme. One of the disadvantages of the technology is the fact that gRNA is always on, that is, it performs its function regardless of the type of cell in which it is located, which can lead to various undesirable mutations in healthy cells. As a result, additional measures are required to limit the regulation of the selected target gene.
To solve this problem, scientists have developed a so-called conditional gRNA, which changes shape in response to the presence or absence of certain substances in its environment. As a result, conditional gRNAs can perform logical functions, such as "if X, then Y" or "if not X, then not Y", where X is a marker for a certain type of tissue or a painful condition that determines the editing, silence, or activation of the target gene Y.
New gRNAs are programmed at two levels: sequence X, which controls the place of gene regulation, and sequence Y, which controls the target for the enzyme. Scientists were able to demonstrate on bacterial cells both the on-off of a protein with initially active conditional gRNAs that are turned off by an RNA trigger, and off-on with initially inactive conditional gRNAs that are activated by an RNA trigger. That is, the enzyme begins its work in response to the presence of certain biomarkers, and is deactivated in their absence. Moreover, scientists have managed to transfer one of the mechanisms from bacterial cells to mammalian cells.
Of course, there is still a lot of work to be done, but scientists hope that the invention will selectively treat diseased cells, leaving healthy ones intact.
The article Hannevich-Hollatz et. al Conditional Guide RNAs: Programmable Conditional Regulation of CRISPR/Cas Function in Bacterial and Mammalian Cells via Dynamic RNA Nanotechnology is published in the journal ACS Central Science.
Elena Panasyuk, portal "Eternal youth" http://vechnayamolodost.ru based on Caltech materials: The Swiss Army Knife of Gene Editing Gets New Control.