Mysterious ‘Retron’ DNA Helps Scientists Edit Human Genes

Cells called retrons, which produce single strands of DNA to detect certain viral infections, are deep in a bacterium. For the first time, researchers have been able to modify genes in human cells. A new study suggests that this technique can be used to enhance gene editing.

Although the well-known CRISPR process has made gene editing much easier in recent years, it has its own limitations, according to a study by a bioengineer at the University of California, San Francisco. This process introduces an enzyme called Cas9 to cut DNA segments and provides templates of desired DNA, designed by researchers, for cells to incorporate during the repair process. The template DNA is created in the laboratory and must be inserted separately from the components of the CRISPR system.

The retrons were used by Shipman and his colleagues to make the DNA inside the cell. The reverse transcriptase that retrons carry builds DNA strands. Santiago Lopez is a graduate student at U.C.S.F. and the lead author on the study.

The researchers modified retrons in the lab to make the desired template DNA. The change to theRNA loops allowed each retron to produce more DNA copies. They inserted the retrons into the cells.

The retrons produced by this process are ten to 100 times more in yeast cells than in human cells. The retrons achieved better editing precision in yeast than in human cells, possibly because of the differing number of strands or the way each cell type repairs DNA.

If we can use retrons to produce DNA within a patient cell, it can be used for gene therapy applications for diseases such as sickle cell anemia, which require repair of only small stretches of faulty genetic.

Jin-Soo Kim, director of South Korea's Center for Genome Engineering, says introducing foreign DNA into human tissue cells can cause adverse immune responses that limit genetic modifications. Kim says that researchers who are using CRISPR alone have developed processes to suppress such responses, but it remains to be seen how to accommodate retrons.